17 January 2014

Adobe Floor Basics - How to build a dirt cheap floor

Seems crazy, right?  A dirt floor, of all things!  Well, time for a perception shift...
Adobe floors are lusciously beautiful and quite durable.  And best of all, in most regions they can be made from local clay soil.  (Which makes them dirt cheap...sorry, couldn't resist.)

adobe floor in a strawbale cottage in WV

The Concept

An adobe floor, or earthen floor, relies on the sticky binding properties of clay...one of the most versatile building materials I know of.  Clay expands when wet, creating sticky platelet particles, like a bunch of suction cups.  Add to the clay ample course sand, to increase compressive strength and control shrinkage as the clay dries.  Finally add fiber, to increase tensile strength and knit everything together, like reinforcing bar in concrete.  The finish mix is essentially the same as adobe or cob.  And the installation is similar to a concrete slab, only without the environmental impacts or cold nature of cement.

What I describe below is the method I use to install an adobe floor.  It is by no means the only method!  I recommend reading with the intention to gain an understanding of the concept...the function that each layer serves.  This way you can adjust and experiment while being sure to include the primary functional characteristics (most particularly to keep moisture out of the floor).

The Layers

A typical adobe floor includes a build-up of layers, each with a purpose.  I describe each layer below, including the function it serves and (in some cases) alternatives you can experiment with.  This example demonstrates a floor installed "on grade", similar to a concrete slab.  You can also install the adobe on a framed floor, but be sure to stiffen the joist framing to minimize flex, otherwise your floor will crack over time.  There are a variety of methods for building up the floor layers, from single pours to multi-layered finishes.  I am sharing a basic version that is conceptually similar to pouring a concrete slab.  I find that this system performs extremely well and is very forgiving to install.

sketch of adobe floor layers

So, starting from the bottom up...

#1: The substrate

You want your floor to rest on solid ground (or a stiff framed floor with little flex).  If you have movement below, it means cracks up above.  So you want structurally strong, compacted earth to build on.  The ground should be free of topsoil or high organic matter, since the organics will continue to decompose and shrink in volume over time, leaving you with voids below your adobe floor.  So dig down until the soil feels solid and compact.  You may even want to go over the ground with a hand tamper to ensure compaction.

#2: The capillary break

Next you install several inches of gravel to provide a capillary break that prevents any potential liquid water in the ground from rising up into the floor.  I use 4-6" of pea gravel or angular 1-inch stone.  If you live somewhere where pumice is commonplace (or any insulating mineral/rock), you can substitute the pumice for the stone & the insulation (#4), since the pumice will provide both qualities.

#3: The vapor barrier

Next you lay a vapor barrier that covers the entire floor area.  This provides your final moisture control for the adobe, blocking any air-borne vapor (from evaporated ground moisture).  I use 6 mil polyethylene sheeting for this, exactly what is used to prepare a concrete slab.  The plastic is obviously not natural, but it's excellent insurance.

#4: The insulation

This is probably the layer that is most often left out, but it can dictate the energy performance & your comfort level.  If you live in an exclusively hot climate, then you can skip the insulation, because a cool floor is beneficial.  But if you heat your building at all...at all...then you want to keep the heat inside.  If you do not have insulation below your floor, then you are, in effect, heating the endless thermal mass of the ground below.  I use R-10 insulation for a typical floor and bump up to R-15 if the floor will have radiant heating in it.  You want that heat to follow the path of least resistance into your space, not down into the ground.  And you need that insulation to be non-biodegradable, otherwise it will compost under your floor and disappear over time, leaving you with a cracked & heaving floor.  This is one place where I will use rigid foam, since the reduction in energy over time quickly offsets the impact of the foam manufacture.  For a natural alternative, you can use rock wool insulation or an insulating mineral, such as pumice or perlite.

vapor barrier (black plastic) with insulation above

#5: The base layer

I do a 2-layer adobe floor, mostly because this allows me to pour the thick base layer before the exterior walls are completely closed in.  That extra air-flow speeds up drying time (and eliminates a highly humid interior later in construction).  I use the same proportions I would for cob, which is generally 15 to 25% total clay plus 75 yo 85% concrete sand.  The difference is that I add lots more water.  With cob, the wetter your mix, the more your cob wants to splooge on your walls, so it prevents you from building higher until the material dries.  However, with a floor, you want to be able to pour it, like a really thick liquid.  (I use about the consistency of chocolate pudding.)  If I am using clay soil from the site, I sift it pretty large...through a 1/2" screen is fine.  To this mix, you want to add long fiber, and lots of it.  The fiber knits the floor together and helps prevent cracking in the clay.  I use straw, since it is abundant in my region.

The process for laying this layer is pretty simple.

  1. make a batch of your mix
  2. place the mix at the farthest corner of your floor, where you are going to begin
  3. make sure you have height reference points in place (such as a perimeter beam or braced ledger boards)
  4. roughly pack the mixture into place, being sure to push into any corners or voids (you can literally throw the adobe into the corners to be sure you get good fill); make sure your material is filled a bit higher than you want your finished layer to end up
  5. level the floor with a long, straight 2x4 by holding each end of the board on your ledgers (so you know your height) and then shimmy the board back-and-forth while pulling slowly toward you (the longer your leveling board, the more hands on deck you need to shimmy it); as material builds up in front of your board, it makes it more difficult to move the 2x4, so simply stop, scrape the excess out of your way, and carry on
  6. then let the floor dry completely (and don't let it freeze until it is 100% dry)

Note that it is perfectly normal to get some sprouting in your floor as it dries.  Do not be alarmed if this happens!  It's just seeds from your straw confusing your floor for a garden.  As soon as the floor dries, the sprouts will die, leaving behind some additional fiber reinforcing from their root structure.

Another option for this base layer is to make adobe bricks.  You are using the same exact mixture but placing it in forms and then letting the adobe dry out in the sun.  The benefit here is that you can carry on with construction, without having to wait for a thick, wet floor to dry so you can walk around unimpeded.  Once your bricks are dry, you lay them like patio pavers in a layer of sand, tamping them to level as you go.

leveling the adobe with a long, straight 2x4

this first layer just needs to be level, but it can have pock marks
(this 550 SF floor took 1 day for about 15 people to install)

#6: The leveling layer

There are a few approaches you can take for this layer.  What I do is float this layer smoooooth and then polish it as it hardens.  Some people float this layer reasonably smoothly, and then apply a super thin layer for the desired texture.  The benefit of polishing this layer as your finish floor is that you avoid the extra step of additional layers.  The benefit of applying a thin final layer is that it's easier to control the texture of a thin coat than it is to control the texture of a thicker poured floor.  So you can decide which is less stressful to you...  But either way, the goal of this layer is to end up with a floor that is level (and if it's your finish, then level & smooth).  In the first layer, small imperfections are not a concern, but this layer is what you will see for years to come.

This second layer uses the same adobe mixture as the base layer, with two modifications:

  1. if using clay soil from the site, I sift it a bit finer...I use 1/4" screening for this layer
  2. any straw in this layer should be chopped to 1" or shorter
Why these changes?  Because smaller particles allow you to float the floor to a finer finish.  I don't always use straw in this layer of the floor, since it will show in the finish surface and not everyone wants/likes that look.  If you eliminate the straw, then it is absolutely crucial to get the ratio of clay to sand perfect.  To do this, make some test patches of your floor and see how they dry.  If they are crumbly and weak, there is not enough clay.  If they crack, there is not enough sand.

The process for laying this layer is as follows.

  1. make a batch of your mix, making sure that it is fairly creamy; wet it just enough so that when you hold a handful flat in your hand it keeps a mounded shape until you vibrate your hand slightly, then it flows like a liquid
  2. make sure you have height reference points in place; I use screed boards that are the same thickness as the floor I want to install (for example, I use a flat 2x for a 1-1/2" thick floor)...see photo below
  3. start at the farthest corner of your floor (and work your way out toward an exit path), and work in swaths that you can easily reach without over-extending your body
  4. roughly pack the mixture into place, being sure to push into any corners or voids (you can literally throw the adobe into corners to be sure you get good fill); make sure your material is filled a bit higher than you want your finished layer to end up
  5. use a very straight 2x4 (or 2x6) that is long enough to touch 2 of your screed boards, push down to create firm contact with the screed boards, and then shimmy your board side-to-side to level the floor; as material builds up in front of your board, simply stop, scrape the excess out of your way, and keep going; the floor shape should be pretty level, but you may have some voids here and there
  6. I then use a wood float or a magnesium float and fine-tune the surface; add little bits of material if you need to fill any voids, and just keep working the surface until it is level and reasonably smooth (see photos below for examples of what it will look like)
  7. your final pass while the floor is wet is with a flexible pool float; this will bring a bit of water (and with it, clay) to the surface and allow you to really make the surface look pretty; but don't go over the surface too much here, or you will bring too much clay to the top and the floor will crack as it dries
  8. continue until your floor is completely installed, moving the screed boards as you go
  9. Finally you will burnish the surface of the adobe floor as the clay becomes leather hard (firm enough that you definitely couldn't trowel it anymore, but soft enough that you can just barely make a thumb print in the surface); slightly mist a small area with water and make quick, tight circles using a very flexible float made from steel or plastic; the amount of pressure you can apply will depend on the dampness of the floor; you should see a slight sheen on the surface as you burnish and any hairline cracks will be pushed closed; if you wait too long to burnish, the clay will be too dry & hard, and you will need to skip the burnishing
  10. then let the floor dry completely (and don't let it freeze until it is 100% dry)

beginning the final 1-1/2" layer

floating the floor level, first with a 2x4, then with a magnesium float to fill all the voids

working from every direction to meet in the middle

a flexible steel float makes the finish super smoooooth

you can see each step...rough placement, wood board leveling, and smooth finish

Watch my trowel primer to understand different types of floats and how best to use them:


#7: The finish

There are several options for finishing your beautiful adobe floor.  (Have you noticed the trend that there's never just one way with natural building?)

If you chose to apply a thin final layer of clay, you have 2 options:

  • apply an 1/8" finish layer, much like a clay plaster, but applied to the floor; when this layer is dry, seal as described below; you can find more info and a recipe HERE
  • apply 1 to 4 coats of clay paint, also call "alis"; when this layer is dry, seal as described below; you can find more info and a recipe HERE
If you chose to burnish your floor, then as soon as the clay is completely dry, you are ready to apply a sealer.  The sealer densifies the top layer of clay (making it more durable & scratch resistant), prevents dusting (so you don't get clay on your butt when you sit on the floor), and reduces absorption (so makes it more stain-proof & easy to clean).  The most common sealers are hardening oils, which react with oxygen in the air to chemically change into a hard, transparent, water-resistant, but breathable resin.  Hardening oils include linseed oil (derived from flax seeds), hemp oil, tung oil, walnut oil, etc.  The oil is applied in multiple layers, and each subsequent layer is thinned with a solvent to promote deep absorption into your adobe surface.  Common thinning solvents include citrus solvent (d-limonene based, ie orange peel) or mineral spirits (petroleum based).  There are alternatives to oil & wax sealers, so feel free to do additional research & experimentation on that.  (The most intriguing of all sealers to me is cow urine.  Yup, not a typo...cow urine.  Traditionally used in parts of Africa and apparently makes for a stunning floor.)  You can also add pigment to your sealer if you want to enhance the color of your floor.

Here are the layers I most commonly use to seal a floor:

  • 1st coat - pure hardening oil (1 gallon covers approximately 200 SF when applied full strength)
  • 2nd coat - 80% hardening oil with 20% thinning solvent
  • 3rd coat - 60% hardening oil with 40% thinning solvent
  • optional 4th coat for high traffic or damp areas - 40% hardening oil with 60% thinning solvent
  • optional beeswax paste to finish - if you want a really luscious surface that feels like leather, then I highly recommend a final coat of beeswax paste buffed into the surface of your sealed floor

Note on smell...the oils harden by oxidizing, a chemical process that offgases an aldehyde compound.  Aldehydes are technically a VOC, though the particular compound offgassed from oils as they oxidize has extremely low toxicity (unlike their cousin, formaldehyde, which is carcinogenic).  However, there is definitely a smell that can linger (especially from linseed oil) and some people with respiratory issues may experience discomfort.
the finished floor

Additives

There are loads of variations on the mix for adobe floors, including additives to enhance various properties.  Common additives include cow manure, prickly pear cactus juice, hydrated lime, milk protein (casein), wheat paste, pigments...even blood protein.  Look for a future post describing the benefits and characteristics of the most common adobe, cob, and clay plaster additives.  (I'll update with a link here when that post is complete.)

20 December 2013

Comfy Cob Bench Ergonoics

Love the look of a cob bench but not sure if clay will be comfortable to sit on?  Comfort is more about ergonomics than the surface material.  A cushy couch can be uncomfortable, which a wooden chair can be superbly comfy.  The difference...they key...is how the body fits on the seat.


cob bench at Black Ankle Vineyard's Tasting Room the I designed & built in Maryland

Here are some tips for building an ergonomic, comfortable bench:

  1. The height of the seat should allow you to sit with your feet flat on the ground in front of you.  Otherwise the lip of the seat will cut off the circulation in the back of your thighs and your legs will fall asleep.  15 to 17 inches high is about right for most people.
  2. The depth of the seat should be deep enough but not too deep.  If it is too shallow, then you are literally sitting on the edge of your seat.  If it is too deep, then you can't sit back comfortably against the backrest.  14 to 18 inches deep is about right for most people.
  3. The seat should slope down slightly toward the rear.  This lets you nestle into your spot.  A 5-degree slope is about perfect.
  4. The backrest should support you and slope back slightly.  The ideal angle between the seat and the backrest is about 100 to 110 degrees.
  5. The base of the bench should give you room to pull your feet back toward your body.  When your knees are less than a 90-degree angle, your quads are more relaxed, so the sitting position if more comfortable.  So the front face of the bench should slant away from the front edge of the seat (instead of going straight down to the ground).  The point where the base meets the ground should be at least 3" back from the front of the seat.
The biggest tip of all, is to test your seat out as you build it.  Literally sit on it as you build.  See if it feels good.  See if your feet can comfortably touch the ground.  See if you can lean back comfortably on the backrest.  Keep testing and adjusting until it feels perfect to you.  And most importantly...have fun cobbing!

02 December 2013

Three Strawbale No-No's

Strawbale construction has been enjoying an international revival over the past few decades.  That revival began in the Southwest U.S., a very dry climate with minimal rainfall and very low humidity.  Why is that relevant?  Because many of the methods of construction developed in the 1980's in that arid climate are still presented as "best practices" details...however, what works in a dry climate does not necessarily work well in a wet climate, where details need to address condensation, rainfall, snow melt, and more.

I would like to reset the standard on how strawbale buildings are constructed appropriately in wet/humid climates.  First, let's dispel the myth that it is not wise to build with straw in a wet climate.  You can read more details HERE, but the bottom line is that anywhere that you can build with wood, you can build durably with straw, because straw and wood are biologically similar.  Second, let's talk specifics about three common details seen in books and on the internet.  These three common strawbale practices may work fine in super arid climates but are NOT appropriate for wet climates.  (However, you can transpose wet/humid climate details to any dry climate.)

#1 Do not pin strawbales with internal rebar

Why?  Rebar is steel reinforcing used to strengthen concrete.  The metal is an ambiently cold material, that is, it remains cold to the touch unless there is a heat source.  When humidity is present, moisture in the air condenses into a liquid along the cold surface of the metal.  The result: a constant drip of water down the metal whenever the air is humid.  That water will eventually build up above 18%, at which point, decomposition of the straw will begin.
Additinally, steel requires a lot of energy to manufacture and is way way way stronger than is needed to hold fuzzy strawbales together.

What to do instead?  Pin your strawbales together with any ambiently warm material, such as bamboo stakes or wood dowels.  Both are strong enough for the job of holding bales together and since both have the same ambient temperature as the straw, you will not create a condensation point inside the wall of straw.

inserting bamboo pins into a strawbale wall


#2 no cement stucco

Why?  Cement is a non-breathable finish material, which means that it blocks air-borne moisture (humidity) from transferring through it.  Additionally, cement is a brittle material, which means that it develops mini cracks with any movement of the building (and all buildings have movement).  What happens is that the cracks allow moisture into the wall and the lack of breathability prevents that moisture from drying back out.  The result is moisture build-up over time.  And again, if/when that moisture gets to 18%, any biodegradable material will begin to decompose.

What to do instead?  Use breathable plasters & finishes, such as clay-based plasters, lime-based plasters, and natural (non-polymer) paints, that allow humidity to transfer freely through the wall.  I use lime plasters outside to save on maintenance and clay plasters inside because they are so beautiful and wonderful to work with.  For paints, I use natural, mostly home-made paints (you can read more on how to make natural paints HERE).

finishing touches on a clay plaster


#3 no gravel base

Why?  Most stone, like metal, is ambiently cold....that is, cold to the touch at room temperature or below.  So, like the example of metal above, the stone creates an artificial condensation point inside your wall.  Consistent condensation means build-up of moisture over time, and...you get the picture by now...eventually you get to that 18%, and decomposition begins.
Plus, you have just built this super-insulated strawbale wall and then eliminated insulation along the entire base...so huge thermal break in your wall system.

What to do instead?  Your base should contain only insulating and ambiently warm materials, like the straw.  There is a stone that will work for this application...pumice...which is a volcanic rock that has many air pockets, making it an insulating material.  But otherwise, you can use any insulation material, such as light-clay-straw, vermiculite or perlite, wood chips, or even reused packing peanuts.

wall base detail under a strawbale wall, with rigid foam insulation


So let's shift these three common details and build durably for wet climates!!

RESOURCES
Here are my 2 favorite books on how to build appropriately with strawbales in wet climates.  All of the authors live & build in snowy, wet, humid climates.

         
click the book covers above for more info or to purchase

07 November 2013

Who Does What...during construction of a natural building?

A question came up during a recent workshop that seems worth exploring further...Who does each task when constructing a natural building?  The answer is, of course:  it depends.  (If you know me, you saw that coming a mile away!)  What depends are the goals & priorities of the Owner...

       ...do you want/need to finish construction quickly?
       ...is cost saving paramount?
       ...do you want to participate during construction?  (and to what extent?)
       ...would you like to hold workshops or work parties?
       ...is high quality craftsmanship important to you?

And then creating a structure for who does what that best suits your particular goals.

Strawbale home built by a contractor -- high quality all around, but also higher cost
More project pics here:  Will & Wendy's Home Photos


So let's back up a bit and define the different roles that get you from an idea, to a home you can live in.

First, you need a design for what you are building.  That design should be suited to your climate and the piece of land you build on.  Some jurisdictions will allow you to draw up your own design.  If that feels overwhelming, you can purchase pre-designed natural home plans or you can hire a designer/architect to create a custom design.

Second, decide who is going to be the coordinator for the project.  In conventional construction, this is the general contractor.  This person makes sure construction occurs in the proper order and makes sure any trades (electrician, plumber, etc.) and inspections are scheduled at the proper times.  This can be done by the Owner!  In which case I have one recommendation...if you have never built anything before, do some research on contracting skills before you take this on & I recommend creating a mentor-type relationship with a local builder to help in case you get stuck head-scratching.

Third, decide who will do the natural building!  You can hire a professional to do some or all of the natural building.  You can host workshops led by an experienced natural builder.  Or you can lead work parties with a group of friends & family.  On this one, be realistic about how much of your time you can dedicate to sweat equity.  Be realistic about your expectations for finesse of finishes, especially if you have minimal construction experience.  And I strongly recommend working with a natural builder, at least on a consulting basis, to help problem-solve anything unusual that may come up (and to give you peace of mind).

Fourth, remember the specific trades.  These include excavation, concrete work (foundation), plumbing, electrical, any wood structure (framing, timber-framing), trim work, cabinet installation, etc.  Be realistic if each of these is something you could do, considering skill-level as well as time.  And note that in many regions, some of the specifics must be installed by licensed tradespeople (most commonly this includes electrical and plumbing).

Strawbale studio built mostly with workshops & sweat equity by the Owners -- less expensive, with a hand-built aesthetic.  More project pics here:  Beth's Cottage photos


What scenario is right for your project?

There are many many ways to structure a construction project in terms of who does what.  Everything from pure Owner/Builder to hiring a General Contractor to do it all...or...a hybrid collaboration between the Owner and a Builder.  If your builder does not have experience with natural building, you likely also will need support with strawbale or cob or cordwood or whatever natural building materials you have chosen to use.  The bottom line, is that you should expect to be more involved during construction, and this is probably one of the things that is drawing you toward building naturally in the first place.

But how do you structure a scenario that makes the most sense for you??

One of my favorite pieces of advice when undergoing construction is that you can choose TWO of the following three priorities:

  1. speed
  2. low cost
  3. quality

So, to decide what type of construction collaboration is going to be right for your project, choose which 2 of these priorities are most important to you.

If you choose speed & low cost...then you are a good candidate to act as your own contractor and host work parties for the natural building features.  This scenario puts a burden on you to be informed...about construction timelines, about finding tradespeople as needed, about the proper way to install your natural building materials, about finding materials, about what you want, etc.  What you may not be able to control with lots of unskilled labor is the quality of the final finishes.  You will dedicate maximum time input, so be realistic that you have a chunk of a few months that you can dedicate pretty exclusively to your construction project.  Your payoff is that you have your building completed quickly and for a minimum financial investment.

If you choose low cost & quality...then you may still want to act as your own general contractor, but you are a good candidate to hire a professional natural builder to lead your workshops.  You may also want to explore using salvage building materials and take the time to really hunt for items you love aesthetically.  This scenario requires patience.  You will still likely contribute a lot of sweat equity during construction, especially fine-tuning the natural building elements.  You may want to personalize the space by sculpting walls or you may invest in some more time-consuming finishes (mosaic, tadelat, polished clay with wax buffed in...)  Some weeks you may feel like you are not making any progress.  But you will get there, and your payoff is that you have a beautiful building for less money than you would have spent if someone else had done all of the work.
For more tips on salvage hunting, see "One Person's Waste...is another's treasure"

If you choose speed & quality...then you likely will hire a general contractor to oversee your project.  You may still want to participate during the natural building portions of construction.  And I would definitely recommend hiring a professional natural builder to lead workshops or to train your contractor's crew.  In this scenario, your energy is focused more on decisions...aesthetic choices, how/when you want to participate with the natural building (and coordinating that with your contractor), what you want your finishes to look like.  If you find you don't have tons of time to dedicate to the natural building or you can't quite muster the level of skill to make you plaster look like you want, then you have a building crew that can take care of it.  This scenario will cost you more, since you are paying for more people-labor.  Your payoff is a beautifully crafted building with exactly the quality of finishes that you enjoy.

There are obviously hybrids of each of these, but hopefully this helps you clarify what you can & want to do for your natural building project.  And most important...have fun!

Strawbale & cordwood home with lots of salvage materials built by the Owners -- less expensive, but more time-consuming to build.  More project pics here:  Scot & Linda's Home Photos

23 October 2013

Lime Over Clay...When is that ok?

There is a commonly held misconception that I would like to correct:  just because lime plaster works as a protective coating for cob buildings (with thick walls built from clay, sand, & straw), doesn't mean that lime plaster works as an exterior protective coating over thin clay plasters.

What am I talking about?  I am talking about the practice of applying a clay plaster base coat over exterior strawbale walls, and then finishing over the clay plaster with a more durable plaster made from lime putty.  The idea is that
          a) clay plaster is easier & more pleasant to apply
        and
          b) it must be ok to use lime over clay because lime works as a finish on adobe and cob walls.
However, this method of using lime plaster over clay plaster actually could lead to failure of your plaster and potentially also moisture build-up in your strawbale wall over time.

Exterior plaster is usually applied in 3 coats:

  1. First, the scratch coat - the purpose of this coat is to get a really good bond to your wall substrate (so for strawbale construction, this means your first coat is stuck really well to the surface of the bales)
  2. Second, the brown coat - this is mostly a shaping coat, to make the shape of the wall exactly as you would like it to look when finished
  3. Finally, the finish coat - this is the coat that gives you the desired texture and sometimes includes integral color

Basic rules for multi-coat exterior plaster...

When applying multiple coats of plaster on the exterior, you can use the same recipe for each coat.  In other words, there is no performance issue if all three layers of your plaster are clay or if all three are lime. However, if you are going to vary your recipe, then the following centuries-old rules must apply:
  1. the layers of plaster/stucco (if not all the same) need to progress from hardest to softest, with softest as the finish
  2. the layers of plaster/stucco (if not all the same) need to progress from least permeable to most permeable, with most permeable as the finish
Why is this?  Well, it has to do with how moisture moves through a wall...

Let's start with the properties of lime plaster/stucco...

Cured lime plaster, chemically speaking, is calcium carbonate...basically limestone.  It's softer & more permeable than cement, but harder and less permeable than clay.  Permeability refers to a material's ability to allow air-borne vapor, humidity, pass through it  Think Gortex...water-repellent and vapor permeable.  Lime plaster/stucco makes a beautiful, durable, breathable exterior finish.



Next, the properties of clay...

Clay plaster is a combination of sticky clay (the binder) and sand (the aggregate).  Clay particles are like sponges that can absorb moisture from the humidity in the air or liquid water from rain, snow, etc.  (The clay particles then release that moisture when the surroundings are dry.)  When clay absorbs water, the particles get fatter, literally increasing in volume (then shrinking as the clay dries).  If you have a fixed amount of moisture that is being absorbed, then thinner clay (ie, plaster) will swell more in volume than thicker clay (ie, solid cob wall).  This means that in the exact same weather conditions, clay plasters will expand & contract, whereas thick cob walls will stay relatively constant.  By itself, this is not a problem, because the clay is flexible enough to withstand the expansion & contraction.


So, what's the problem?

The short answer: it's an issue of thickness & water absorption.  As stated above, clay plasters expand when wet and contract when dry.  In short, they move by swelling and shrinking.  Not a problem if you only have clay.  However, lime plaster is rigid, like monolithic stone.  The way lime plaster deals with movement is that it forms a crack to allow independent pieces to move independently.  Sooooo, if you have a substrate of clay, that is expanding and contracting with the weather, and you have a finish surface of lime, that cannot handle movement....then the natural movement of the clay will result in cracking in the lime finish plaster (that you wouldn't have if you just used clay or just used lime).

The second problem is technical...when you have a soft substrate under a hard, less permeable finish, then over time moisture actually erodes the substrate (ie, the clay plaster) right out from under the finish (ie, the lime plaster).  This is seen dramatically in cases where adobe buildings were finished with hard, impermeable cement plasters, resulting in erosion of the clay right out from under the cement, leaving nothing for the cement to bond to, and whole chunks of the cement stucco just fall off the walls.  While lime is not as hard and as impermeable as cement, it is harder and less permeable than the clay, so the process may take longer but the same result is at risk of occurring.

How do I know?

Maybe this all seems theoretical.  It did to me too.  Soooooo, I built a test...a small strawbale building in my mom's yard...to test the theory out and find out exactly what would happen.  (My poor mom!)
angled strawbale walls with deep roof overhang
(the drip line of the roof is over 42" from the base of the strawbales)
The walls are strawbale, with deep roof overhangs to protect from any direct rain.  So the moisture that interacts with the walls is almost entirely from humidity.  Over the straw, I applied 2 coats of clay plaster, totaling approximately 1-inch thick.  I let the clay dry completely and made sure the clay surface was crack-free.  Over the clay, I applied two coats of lime plaster.
2 coats of lime plaster over 1" of clay plaster
Then I waited a year.  My theory was that the thin clay base coat would expand and contract with changes in humidity, and that movement would cause the lime plaster to crack (since lime is not as flexible to movement as the clay is).
large cracks in lime plaster (over clay sub-plaster)
And here's what happened....in less than one year, with no direct moisture, rain, water anything getting on the walls, the clay sub-plaster had swelled & shrunk enough (from just humidity changes) to dramatically crack the lime plaster.  It's normal to see hairline cracks in lime plaster after several years, but not huge cracks like this and not within one year.  Hairline cracks will mostly self-heal, or can be lime washed.  But larger cracks like this need to be completely protected from rain or will require repair.


The bottom line...

My recommendation in regions with humid or wet weather, is to use an exterior plaster that is consistent in all three coats...either all three clay or all three lime.  Use all clay plaster if the walls are very protected from any weather or if you don't mind an annual replastering party.  Use all lime plaster if you want a more care-free, water repellent finish.

14 June 2013

Build a Clay (Cob) Oven in Your Yard!

How to build a wood-fired pizza/bread oven using local natural materials

If you are looking for a small project to get your hands (and feet!) dirty testing out some natural building skills, then building a wood-fired oven is a great place to start.  If you have a little help, it takes just a couple days to build, then a few weeks to let it dry out (during which time, you can sculpt your oven to any shape), and then you're ready for a pizza party!!

What is a cob wood-fired pizza oven??  Well...it's a baking oven that is heated by lighting a fire inside, the fire warms up a thick clay oven wall, and the clay wall remains warm for hours after the fire is pulled out.  So you build the fire in the same oven area that becomes your baking space.  The beauty of this type of oven is a) the oven is simple to build using local, natural materials and b) the oven temperature remains very even throughout, with no hot or cold spots.  Plus, it's a fun project to do with a bunch of people and you can celebrate your accomplishment with a pizza party!



So, what do you need to know to ensure that your oven project is successful?


FIRST, get this book:

this book contains all of the information you
need to successfully build a cob oven.  Really!

SECOND, decide what size oven you want to build.

The appropriate size for you will depend on how you intend to use your oven.  Here are the variables effected by size:

  1. The larger the oven, the more materials you need to build it.  For example, an oven that is 36" wide inside takes about twice as much clay, sand, & straw as an oven that is 24" wide inside.  And more materials translates to more building time as well.
  2. The larger the oven, the longer it takes to heat up.  For example, a 24" wide oven takes about 2 hours of fire to heat up, whereas a 36" oven takes about 3 hours.
  3. The larger the oven, the more mass, soooooo, the longer the oven stays warm.  This means you can cook in it longer each time you fire it up.  Especially if you a good insulation layer on your oven.
  4. And obviously, the larger your oven, the more pizzas you can bake at once!  (Or whatever you are cooking...)
So, think about how long you want to wait for your oven to heat up, how long you want the oven to stay hot (larger oven for pizza party use, smaller oven for personal use), and think about how big of a project you want to take on (do you want to build a small oven over 2 days or go for a larger oven and spend longer to build)??
Typical sizes are 22-1/2", 27", or 36" (these sizes work out well with the size of standard fire brick).  Of course, there are mini ovens as well as massive ovens, but those are mostly for special use applications.

THIRD, decide if you will build a roof over your oven.

A roof will help protect your oven from the elements, and allows you to bake even when the weather is sucky.  Rain, especially, will erode a clay oven over time.  You can either allow that, replaster your oven every year, put a tarp over your oven when it's not in use, or....build a roof to protect it.  If you decide to build a roof, those materials will be in addition to those listed below.  Build your roof so you have plenty of room to stand underneath, and to clear any smoke out.  I recommend at least 7 feet of clearance under the roof.

FOURTH, gather your materials.

You will need the following materials to build your oven:

  1. Clay:  Clay is your essential ingredient, because it is the binder that holds all the materials together.  When wet, clay is sticky.  When it dries, it is strong & hard.  You can use clay-soil OR you can purchase dry, bagged, pottery clay.  (see video below on how to test your soil for clay content.)  If you are using clay soil, you will need to determine the proportion of clay in your soil (it may feel like it's 100% clay, but it rarely actually is...usually there is sand in there as well).
    HOW MUCH?  The amount of clay needed depends on the size oven you are building.  Here I am talking about total clay, so if you are using soil with clay in it, you will calculate the amount of clay based on the percentage of clay in the soil  (So, if your soil is 50% clay & 50% sand, then every bucket of soil = 1/2 bucket of clay & 1/2 bucket of sand.)  So total clay needed is about 25 gallons for a 22-1/2" oven, about 35 gallons for a 27" oven, and about 50 gallons for a 36" oven.
  2. Sand:  Sand is your aggregate.  It reduces shrinkage of the clay as it dries and it adds total strength to your oven walls.  You need to use angular sand, not smooth sand or silt.  Concrete sand is pretty cheap & works great.  I also use sand to build the form for the oven (this sand is taken out at the end and can be used to make plaster if you finish your oven that way).
    HOW MUCH?  Plan on about 300 to 500 lbs of sand if you are using clay soil with at least 50% sand content; if you are using bagged pottery clay, double the sand.
  3. Straw:  Straw is used to create an insulating layer for your oven.  It is also helpful to stand on the bales as your oven gets tall.  Make sure your straw is clean, dry, and mold-free.
    HOW MUCH?  You need about 2 to 3 strawbales for a small oven and 3 to 4 strawbales for a larger oven.  If you plan to sculpt your oven into a fun shape, make sure you have ample straw.
  4. Firebrick:  This is what I like to use for the floor of the oven, because they don't split in the heat of the fire and they have extremely squared edges, so they make a really smooth floor.  Typical firebrick are 4-1/2" x 9" x 1-1/2".  You can lay out the bricks for your desired oven size to see exactly how many you need, but below is what I use as a reference.
    HOW MUCH?  I use 15 firebrick for a 22-1/2" oven (12 for the floor + 3 for the door opening), 22 firebrick for a 27" oven (18 for the floor + 4 for the door opening), and 37 firebrick for a 36" oven (32 for the floor + 5 for the door opening).
  5. Water:  you will need a running water source to wet the clay binder.  (and is helpful for clean-up)
  6. Newspaper (optional):  I use this as a layer between my sand form & the first layer of clay...it lets you know when to stop digging out your sand so you don't accidentally gouge your oven wall.
  7. Stones or brick or urbanite (optional):  I recommend building your oven up on a base so you don't have to kneel on the ground to tend your fire & bake.  A comfortable height is typically 24" to 36" off the ground, but choose whatever height is comfortable to you.  You can use any kind of masonry material that is available to you, and you can make cob (clay, sand, and straw) to make a strong mortar.  Just make sure that your oven base is very stable.  Once the base is built & dry, don't forget to fill in the center (with something sturdy & non-compressible), so you have something solid to build your oven floor on.
Note: I highly recommend collecting extra material than you think you need so you don't run out of anything mid-stream.

How to test your soil to see if it has clay in it:


And this is my tools list when doing an oven workshop:

  1. buckets - I like to have ample 5-gallon buckets; you these to transport and measure your materials; to me, 5 buckets is a minimum, but if you are working alone, one bucket will work
  2. tarps - I like to have 2 tarps, but one works; 10' x 10' seems to be a manageable size
  3. shovels - if you are working alone, one shovel is fine; if you are going to have a bunch of people, have at least one shovel for sand & one for clay (more if you will have lots of helpers)
  4. sifter - if you are using clay soil dug out of the ground, I find it easiest to sift it roughly through a 1/2" screen to remove any rocks & to break up the clay and make it easier to mix; I like a table screen that fits over a wheelbarrow
  5. a wheelbarrow is useful to transport material, but is not essential


FINALLY, build your oven!

STEP ONE: Build your base

I like to make a shallow foundation filled with gravel to help keep the oven from moving with freeze-thaw cycles in the ground.

You can build your base with any masonry material - this example uses old cobblestones from the streets of Philadelphia, built with a cob (clay, sand & straw) mortar mixture.

STEP TWO: Fill in your base & build the oven floor

Fill in the base of the oven with a non-compressible material, like tamped gravel.  Then add a 4" or so layer of sand that extend just above the sides of your base.  Tamp and level that sand.

Then build your oven floor with the firebricks, making sure they are nice & tight to each other.  Tamp your bricks and make sure they are nice & level.  Spend some extra time here...the nicer your oven floor, the fewer nooks & crannies that will cause you potential headaches when you are baking.

STEP THREE: Build the form for your oven cavity
Basically, you are building the most boring sand castle ever: a nice dome.  The dome width is the diameter of baking space you want.  The height of the dome will be 75% of whatever your width is.

Add a layer of newspaper over your sand so that when you dig out the sand at the end, you know when to stop digging (before gauging your clay layer).

STEP FOUR: Build the clay mass layer of your oven
 
The first layer of your oven is cob without the straw, so just sand & clay.  You want enough clay so the mixture is sticky, but enough sand so that this layer doesn't shrink (and then crack) a lot.  For most types of clay, that means between 20% and 25% total clay content.  I like to make this layer 4" thick, all the way around your sand dome.  I do not worry about the door at this point...I carve that out later.

STEP FIVE: Add the insulation layer
Your insulation layer is mostly straw, with just enough clay to act like hairspray to hold the straw together.   The idea is to keep the heat inside the oven for as long as possible, increasing the efficiency.   What to do: use a clay mixture that is 50% clay & 50% sand (if that is the proportion in your soil, then you can just use your soil), wet the clay/sand mixture so it is quite soggy...like a chocolate milk shake, then add lots of loose straw, until all of the straw is coated with clay.  Then smoosh it in place.  I use about 6" thick of insulation.

STEP SIX: Cut the door

I like to sculpt the door in the insulating layer.  The straw has really good binding properties, which make it easy to sculpt a nice arch for your door.  If you are not doing a chimney, then the height of the door needs to be 2/3 as high as the inside dome.  This allows fresh oxygen-rich air to come in the bottom of your door opening to feed your fire and the exhaust exits the top of the door area without smothering the fire.  If you make a door ahead of time, you can use that as your template for sculpting & cutting your opening.

STEP SEVEN: Let the oven dry for a few days, then pull out the sand
There are a few strategies for taking out the sand.  I like to carve out the door the day the oven is finished, then pull out about 1/3 of the sand, and then let the oven sit for several days to let the clay mass layer dry out a bit.  Then you can pull out the remainder of the sand without risking any collapse of the dome.  But don't worry, if you pull out the sand too soon and part of it collapses, you can just patch it with the same materials.

STEP EIGHT: Sculpt your oven as desired
Use clay, sand, and lots of straw to make a firm, cob mixture that you can use to sculpt your oven into any shape that makes you happy.  If your oven has begun to dry out when you start sculpting, be sure to wet down the surface before you add your sculpted pieces, otherwise they will not bond to what is existing.  You can also put mosaic tile on your oven, or plaster it with clay or lime plaster.  (This photo shows a lime plaster that is fairly weather-resistant.)

STEP NINE: Let your oven dry out completely & then have a pizza party!
Fire the oven for 2 to 3 hours, with a nice hot fire.  Then let the fire go to embers.  If you made a fairly large oven, you can distribute the coals around the back perimeter of the oven to keep it hotter longer.  Otherwise, pull all of the fire out (into something non-flammable, non-meltable)  and clean the oven floor with a damp cotton mop or cotton T-shirt.
Put the door on for about 20 minutes to let the temperatures come to equilibrium, and then bake pizza, bread, casseroles, cookies, pies, and anything else your heart desires.  As the oven gets to around 100 degrees, you can even use it to culture yogurt.  And keep a well-fitting door on the oven to keep the heat in.




Still not clear?  Watch these videos that show you the step-by-step process for building a cob oven.

Building the floor of the oven & the sand mold for the oven cavity


Building the thermal mass layer (that will heat up when you build your fire) & the insulating layer that keeps the oven hot longer.


Digging out the sand form & baking your first pizza.


Happy baking!!

25 May 2013

Collaborate with the sun...passive solar design basics

Passive solar design takes advantage of solar orientation and other climate conditions to minimize (and in some conditions, eliminate) heating and cooling requirements for a building.

The name says it all...


PASSIVE = no mechanical parts & minimal if any maintenance

SOLAR = uses (free) energy from the sun

DESIGN = integrated into the building design

The result is free heating (& cooling) that works because of how a building is design, so it cannot break.  What a win!  (If I'm ever in charge, all building will have to be designed this way...but that's another story...)



The basics are simple!


1. Properly orient your building relative to the sun

The easiest direction to control when the sun enters your space is from the South side (see #2 below).  This means, that you want to orient the longest side of your building along an East-West axis and a maximum amount of your building faces South.  You can rotate 15-degrees either way without much effect, and rotate up to 30-degrees off that axis and still be over 90% efficient, so you have some play.  But for maximum efficiency, set your longest facade to face due South (North, if you live in the Southern hemisphere...)  And make sure the windows facing South will receive un-obstructed sunshine from at 10 AM to 2 PM (9 AM to 3PM is even better)...this means no buildings, no trees, or anything else that will shade the South-facing windows.  Whatever percentage shade you have, that is the percentage of efficiency loss you have.

2. Use the sun's angle to your advantage

Have you ever noticed that the angle of the sun in the sky is lower on the horizon in Winter and almost overhead in Summer?  Well, you can use that fact to your advantage...bringing low Winter sunshine into a house to heat it (for free) when it's cold outside.  But also shading shading from that hot Summer sun is easy because the sun is nearly overhead...and no sun streaming in during hot Summers means free cooling too (because no heat gain).  You can see a graphic of that below, with a building section through a 2-story passive solar house.  On the lower floor, there is a thermal mass cob wall, 1/2 of which is in full sunlight in Winter.  That means the cob wall heats up (again, for free) during the day, and releases that heat slowly overnight.  That same thermal mass wall is completely shaded in the Summer, so it is a heat sink for excess warmth in the air (ie, it provides free cooling power all Summer).
solar angles on the South side, Winter vs. Summer

3. Size your South-facing window appropriately

The biggest mistake made with a passive solar home is to make the Windows on the South too large.  This means you will end up with too much heat gain (especially in temperate Spring & Fall weather).  The size of your windows is calculated at a percentage of the total space that window will heat.  The percentage used in the calculation depends on the climate where you are building.  Generally speaking, the window area should be between 7% and 15% of the interior floor area.

You also need to consider the size of windows facing North, East, & West.  The windows on those sides help tremendously with the comfort of your interior space, becase windows on at least 2 sides of every room means better quality light & means excellent natural ventilation.  But, consider these tips as well:

windows on the WEST are your biggest source of heat gain, because the angle of the sun at the hottest part of the day in Summer is streaming in at a low angle.  The best way to shade to this side is some well-placed trees.  If you don't have landscape shading, then minimize the window openings on the West.

windows on the EAST can contribute a bit to heat gain in Summer (for the same reason), EXCEPT, that the morning sun is at the coolest time of day, so not quite as detrimental to your interior comfort.  I use windows to the East for balanced morning light and to improve airflow.

windows on the NORTH provide excellent light quality and cannot contribute to heat gain, however, large North-facing windows can mean lots of heat loss in the Winter (since windows are not as insulating as walls. I use smaller windows to the North side, and try to put closets & bathrooms on that side of the house.
typical amount of South-facing window area for a house
(the West has only very small windows and the East is
shaded by the garage; the North side has mostly closets,
bathrooms, and the kitchen, so also smaller windows)

4. Build a closed room at your entry

This simple strategy is often overlooked, but is quite effective.  The principle here is again simple: when you open your outside door, there is a nearly 100% air exchange between inside air & outside air.  That means whatever room your door opens into, loses all of it's warm air in Winter (or cool air in Summer) and is replaced by whatever temperature air is outside.  Simple way to minimize the effect of that?  Open the exterior doors to a smaller room that isn't part of your living space.  This space should be insulated, but does not need heating & cooling (it will stay within 10-degrees of the rest of your house).  But absolutely, positively, it needs a door between that entry room and the rest of the house.  That's what keeps the air exchange to a minimum.
this is a glass door on the inside of an entry space,
with another glass door leading to outside...plenty
of light and connection, without the energy loss

The entry room can also be where you dump coats, hats, boots, shoes, etc.  (Ok, maybe not dump...it can all have a nice neat place to get put, but you get the idea...)

Recommended Reads

This is above and beyond my favorite book on passive solar design.  Out of print, so hard to find, but snag it if you find it...and read it twice!


26 April 2013

Practical Strawbale Specifics: WALL SECTION

I wanted to start sharing some practical nuts-and-bolts information on natural building.  Starting here with some wall sections that describe the construction of a strawbale wall for an actual project.  A wall section is simply an architectural drawing that shows the construction -- bottom to top -- of a wall system.  The notes in this example are somewhat generic, though some are project-specific.  If you click the image you should link to the full size version of this drawing.  WARNING: it's a really large file, so may take some time to load (depending on your internet speed).  Or feel free to download so you can zoom at will.  But please note that this is copyright protected, so do not share or use without express written permission.

This particular project features rubble trench foundations, shown at the base of the wall, and strawbale exterior walls with lime plaster outside and clay plaster inside.  Also shown are roof tie-in, second floor framing, and a lower porch roof where it meets the strawbale wall.  This project (as all of my strawbale buildings) received a standard building permit for construction.

Please feel free to post questions!!

30 March 2013

One Person's Waste...Is Another's Treasure

Salvaging building materials brings new life to otherwise discarded items.  Figuring how to reuse materials can inspire creativity and save loads of money in construction costs.  But you need to have a plan, or you risk spinning your wheels and burning out from all the leg-work involved.

all of the windows for this house are high-quality & energy-
efficient....and yes, they were all salvaged at huge cost savings
Below is the process that I share with my clients who want to make the most of salvage building materials in construction.  The key to success and keeping stress to a minimum is to start early and have a plan!  And don't forget to plan for a place to store what you find that ensures your materials stay protected.

Salvage-Hunting Process...

STEP ONE: make a list

Start by making a list of materials you will need for the project.  This way you know immediately when you see something interesting whether or not you can use it.  Try to avoid just purchasing items with a "maybe this will work...somewhere..." attitude.  You will end up spending a lot of time & money needlessly.
You also will want to track your list.  I use a spreadsheet with at least the following columns:
  • item (doors, windows, sinks, flooring, etc.)
  • location (this helps you keep track of your salvage items)
  • minimum size (what's the smallest your item can be)
  • maximum size (what's the largest your item can be)
  • special requirements & notes (to help you remember any specifics)
The goal is to have a shopping list to take with you as you go salvage hunting, with reminders of any limitations or special needs that each item has.

This built-in nook makes use of a salvaged church pew, cut to fit.
(The client had "two 4-foot nook benches" in their shopping list.)


STEP TWO: prioritize your list

Big items that can save you the most money include, doors & windows (see more info below), cabinets & counters, fixtures, and flooring. Other items can include framing lumber, railings, overstock insulation, patio pavers, etc. You can prioritize your list one of two ways:
  1. By construction timing - which item do you need first, second, third, etc. to keep your construction process flowing smoothly.  I think this method is best if your plan is to do your salvage hunting concurrent with the construction process.
  2. By which items can provide the greatest cost savings potential, such as windows, doors, and cabinets. This allows you to start looking for the items that give you the biggest dollar savings for your time spent, and by the time you get to the smaller items on the list you will be a salvage pro.
If you aren't sure how much energy you have in you for the salving hunt, then I would do option #2.  That way, if you start getting overwhelmed by the salvaging, at least you have collected big savings items.

This interior door is an old salvage door with single-pane glass...
not suitable for exterior use...but great for creating interior sound
separation while keeping visual connection between the spaces.


STEP THREE: research baseline pricing

In order to ensure that you don't overpay for your salvage items, you will need to do a little bit of research on what your items would cost if you purchased them new.  This can feel like a big task when you first start, but you will start to get the swing of it as you become a salvage hunting expert.

This counter is made of 3" thick maple, from a repurposed bowling
alley floor.  The total cost was 10% of what the counter would
have cost for new maple (or other solid-surface countertop).

 

STEP FOUR: don't give up performance

For items that have a performance implication, make sure you take that into consideration.  Otherwise you are saving upfront costs, only to find you need to spend money again later for higher energy bills or for replacement.  Performance criteria include:
  • durability
  • energy efficiency
  • structural integrity
For example, if salvage wood will be used structurally, it should be structural grade, show no signs of rot, be free of compromising holes, etc.  For windows, you will want energy efficient, double glazed windows in good condition. If the windows are used for passive solar gain in the winter, the windows also need to NOT have low-e glazing on them.  For appliances, you still want them to be energy efficient. You get the idea...

These wooden posts were salvage from 75+ year old building.
 The wood is hard and dense, and in great shape.  We had a
structural engineer inspect the wood before using it to build with.
(It could also be milled into beautiful flooring or trim.)


STEP FIVE: put in the time

Salvaging requires quite a bit of time & patience, so keep that in mind as you jump in.  And this is why I recommend starting early so you don't find yourself overwhelmed by a "holy heck we need this door tomorrow" moment.  I have included salvage resources that I find to be the most helpful in the region that I work (greater Washington DC/Baltimore MD region).  Feel free to post comments below to share your favorite building material salvage resources.

This metal railing was reused from another part of the same house!
The addition was built over a flat-roofed garage...the garage had a
railing all the way around, that was removed to build this art room.

Some specific Tips...

Salvage doors and windows usually provide the biggest savings for your time investment.  For windows, you have a few options. One is can find local companies that specialize in selling new & replacement windows. They often have a room in the back of new windows that were ordered wrong or were never picked up...orphans, if you will...that they are happy to sell at a discount.  It takes a lot of legwork, but this is a great way to get high quality, new windows for a fraction of the cost.
Used furniture can be nicely converted into a funky bathroom vanity.  You can check yard sales, local thrift shops, and even drive by upper-income neighborhoods early on trash day.
Another great resource is to check for a local Habitat for Humanity "Restore".  They sell donated, salvaged building materials & appliances at a great discount.  See www.habitat.org/restores to search for a ReStore resale outlet nearest you.  Proceeds go directly back to Habitat for Humanity.


RESOURCES

These are my most-used resources in the Washington DC/Baltimore MD metro region.

www.secondchanceinc.org (in Baltimore)

www.rebuildwarehouse.org (in VA, but they have a lot of salvage building materials)

www.communityforklift.com (just outside of DC, in Maryland)

www.restorenova.org (Alexandria, VA)