Episodes
Naturally Beautiful Walls
"Today we're building walls that breathe. It's time to cover the interior of all our straw bale walls with plaster. Like with the exterior, we're going as natural as possible using earthen plaster. Then we'll add a layer of gypsum plaster with natural colors to beautify the entire house. Where we can't plaster, we're going to paint with natural low VOC paints that keep the air healthy."
— Building Green host Kevin Contreras
Plasters
While the straw bales are the envelope of Kevin's dream home, plaster will be the skin. But Kevin isn't looking for just any plaster, he wants earthen plaster. Earthen plaster, unlike cement, is very permeable. Gas and water, can exit through the walls so that the wall stays nice and dry keeping, which keeps stops condensation and mold growth.
Building Green's health expert, Alyssa Alvord, explains that "modern building systems have created very tight structures, and we want everything to be airtight. However, that's not the best thing, really, for human health."
Kevin's foreman, Michael Gordon, explains that earthen plaster is a tried-and-true way to plaster walls; it's inexpensive; and it maintains the breathability of the straw bale walls.
Inside the Design
Kevin explains that after the earthen plaster is applied, they will add a layer of gypsum plaster on the interior of the walls. These layers will create a skin about two inches thick to protect the straw bales and add to the thermal qualities of the wall.
Generally, straw bale walls are left wavy, but because Kevin wants his to be flat, the bales will need to be trimmed before the earthen plaster is applied.
Saving Green
Earthen plasters are very inexpensive. Kevin bought his clay for $10 a ton. After the cost of the sand and transportation of both things, plus water and straw left over from building the walls, all of his earthen plaster materials will cost him less than $500 for the entire house.
Gypsum Plaster
After the earthen plaster is applied and the walls are even, the gypsum plaster is applied. Perlited, premixed gypsum plaster is a lightweight plaster that is 50% lighter than most conventional plasters. It also offers much higher fire resistance as well as higher thermal and acoustical insulation values.
It is cost-effective as well. Each 80 pound bag costs $16. Over the earthen plaster, each bag covers about five square meters. In the end, the gypsum plater will cost about 36¢ per square foot with delivery charges.
The gypsum can be mixed with water and natural pigment to give the walls color. These pigments are natural water- and oil-soluble powders made from rocks, minerals, and earth.
Kevin decided to go with a neutral color, but it's possible to get almost any color you desire.
Low VOC Paint
Interior
Because not all of Kevin's home is straw bale, he will have to paint some walls in his home, including the garage and the laundry room.
Alyssa Alvord explains that traditional paints can be high in VOCs (volatile organic compounds). "Now," explains Alyssa, "the trouble with these compounds is that they are toxic formulations that emit into the indoor environment up to 3 1/2 years from the time that they have been painted ... For those years, you and your family and your animals are breathing in these toxic fumes that are known to cause a myriad of health problems."
Kevin visits Taja Di Leonardi at EcoHome Improvement in Berkeley, Ca. to find out more about non-toxic paint. Taja explains that a green paint is one that is both zero-VOC and Green Seal certified. This ensures that the paint is non-toxic and durable.
Taja also explains that zero-VOC paint is comparable in price to most traditional paints. In general, it would only cost $200 to $300 more to paint the entire interior of a home with zero-VOC paint.
Kevin decides on YOLO Colorhouse paint.
Stains
Kevin needs to stain his antique doors, but regular stains are full of unhealthy chemicals. Luckily, as Alyssa Alvord explains, there are plenty of non-toxic water- and oil-based stains on the market now.
Easy Green Step
Paint doesn't last forever. The chemicals separate and make the paint unusable and even more toxic.
Take all of those half-empty paint cans out of your garage and drop them off at your city's hazardous waste collection center.
Next week on Building Green: Flooring & Closets
Paint finishes.
I really like the mottled color and texture it creates a nice appearance with a very lasting effect. I watch allot of history in architecture shows on tv and this finish is ancient allot of the old concrete high density villages of earlier times use similar finishes.
EarthBags?
Hello! Can this interior finishing technique be applied to earthbag construction? Will it be suitable for a tropical environment? Thank you very much. This site is very informative!
walls
hello i was wanting to know if this straw bale wall idea would work in Colorado with the snow. Also what would be the best out look to do this. Also how strong are the walls such as hanging pictures and what not .
Bales in Colorado
Straw bales are perfect in Colorado, where humidity is not high and lots of insulation is needed to protect against the cold and the heat. Hanging pictures and things is easy with some planning. We inset wood in the bales as we are building. We trim out some straw, anchor in a 1x6 at the height of the potential picture hangers, and the plaster over it. Then all that’s needed is a nail or screw. Build with straw and you’ll be so happy.
Kevin
Interior plaster
Hi - you mention Yolo as the PAINT you used. What earthen or clay plaster did you use? I love the texture I see. And glad to hear a novice can take a crack at it. Thank you.
The clay plaster we used is
The clay plaster we used is something we got out of our local area. That's the best to do when applying the structural layers. The earthen plaster is made of sand, straw, water and clay. Tests have to be done to determine the quality of the clay and the right mixture.
When you want to finish your walls, look to products by Bioshield or American Clay. They have fantastic, easy to use products that are beautiful, environmentally friendly and actually purifying to your indoor air quality.
Happy plastering,
Kevin
re: plaster walls
If you want to cut into the walls in the future let's say to add plumbing or wiring, how do you do that and repair it? Plaster walls are different than drywall.
Also, how do you find someone to do the plastering? I always thought that plastering was a art. You just can't get anyone to do it. Is there an association?
As for paint becoming toxic. When does this happen? I was told by benjamin moore to put my eco-spec paint in the smallest container possible to not allow air to circulate with the paint. I went and bought smaller containers. It has been 2 years and the paint smells fine. Just curious when I should get rid of it. anna hackman, www. green-talk.com
re: plaster walls
With Kevin's house, he used quick setting (60-90 minutes) perlited gypsum plasters with pigments added. The bales also were covered in wire mesh imbedded into the clay/sand base coats.
True, with this type of plaster substrate, repairs are a little more complicated.
I don't know if the building codes required him to use the wire mesh, but we use a burlap/hemp mesh fabric (5.5 oz) imbedded into the base/finish coats instead. The pigmented perlited gypsum plasters take a little experience to perfect, due to their fast setting and, occasionally, color "drop outs", but are truly beautiful/durable. With this type of finish, repairs would require him to mix up a batch, with the exact recipe of plaster/pigment ratios, and do the complete wall -- from edge to edge (no big deal) -- to match the color. (This applies to veneer plasters over drywall, too.)
However, if he had finished it off with a pigmented limeplaster/limewash (or clay for that matter), he could store the leftover limewash or clay paint indefinitely, similiar to paint. Repairs would be as easy as opening a bucket, mixing, and spreading it on.
True, plasters and limewashing is an art, but it's also good science. You don't have to have experience to create truly beautiful finishes . . . in fact, some of the best ones I've seen are from beginners, or new experiments. And remember, these finishes are not hydrocarbon based: they are crystals of inorganic minerals, each with different light refracting indexes and properties. VERY different from synthetic paints/pigments.
As for paints: stick with the formulas of the masters (Da Vinci, Van Gogh, etc.). Linseed oils, hemp oils, milk paints and other formulas outlast all current technology. They polymerize by oxygenating their unsaturated double-carbon bonds (omega3/6s), not by condensing and off-gassing. Acrylics and other fossil-fuel based paints, regardless of their VOC content, still have nasty plasticizers, defloccuants, dryers, and biocides that are not part of the polymer bond, and hence offgas. Historic/non-toxic paints take longer to cure, but the "need for speed" makes lots of materials more toxic, in application and curing/offgassing.