Natural Walls
Links to the Ask the Experts page

Janine Bjornson is a natural builder, practitioner and educator. She began her career in natural building when she trained with The Cob Cottage in 1996. Since then, she has taught over 65 workshops in Canada and the United States, from east to west. Her passion for building with natural materials bloomed out of her love for the earth, in conjunction with her concern for diminishing ecological resources and toxic buildings. As a result of this, Janine has devoted the last 14 years to immersing herself in the world of natural materials and the knowledge of how we can shape dwellings that are healthy, healing, inspiring, and beautiful. She has developed a penchant for natural paints, and plasters and loves the concept of “naturalizing” any kind of home. She loves to share this knowledge with others and this is evident in her enthusiastic teaching style. Janine has assisted in organizing 2 Natural Building Colloquia. She has presented at the Natural Building Colloquium in Bath, New York, Kingston, New Mexico, and Kerrville, Texas. She taught the hands-on natural building component of New College of California’s EcoDwelling program, and Dominican University’s EcoDwelling program. She lives in Sebastopol, California. www.claybonesandstones.com.

Q: What alternatives are there to using drywall? I live in the pacific northwest and want to convert part of our shop into a yoga studio.

A: The options would vary depending upon the construction of your shop. I will assume that it is typical 2x4 construction. The most obvious one is lathe and plaster. This is what was very common in the past. It involves attaching small wooden slats horizontally to the 2x4 with a small space between each slat. Then you are able to put plaster over this wood. It will slip between the wood and key in and then cover it when applied thick enough. Traditionally it was done in conjunction with gypsum plaster, but you could also use an earthen plaster if you wish.

Q: I'm making some straw clay infill in our old wood frame cabin, in preparation for plastering. It seems as though adding borax will reduce mildew/ mold growth would be a good idea, as it is likely to get rained on before it dries out. Question is: How Much borax to add to the clay slip?

A: I have used something up to 5% by volume (of your clay slip) of Borax to the mix. Make sure that you dissolve it in hot water first. I would make sure that it does not get wet before the plaster time. You should cover it if there is a danger of that. You should not be plastering it
if it is not dry either. Mold can grow and and work it's way through the plaster and leave unsightly marks. I would only suggest plastering it if it is all completely dry.

Q: We just moved into an earth-bermed, concrete block house with the blocks painted glossy (interior). It has a concrete slab and no flooring since I ripped up the carpets. I'm having a hard time finding information on combining this type of conventional building with more natural finishes. Would it work to sand the paint and apply cob and natural plaster to these drab walls?

A: Yes, it would work to sand the walls and apply a thin coat of earth plaster, natural or clay paint. Applying a thick coat of cob would be more labor intensive and not necessary (most likely) to achieve a natural wall finish for the outside of the bricks. I would suggest applying a couple coats of Alis paint (clay paint) applied to the wall if it is in good condition. I have used Alis successfully in this application and it is a beautiful and inexpensive solution. For more information on 'Alis' consult "The Natural Plaster Book" by Cedar Rose Guelberth and Dan Chiras. Or contact me directly for consultation. Whatever plan you choose to embark upon, there are a couple of main concerns you are looking at for a successful wall finish.

1) Mechanical bond. The current wall surface is very slick and smooth. This prevents plaster or paint from being able to 'key' onto the wall surface. Sanding the paint will rough it up so you may apply certain wall finishes. You may also paint on a adhesion coat to the surface of the glossy paint. There are various recipes for this kind of coating. One option is to use a binder of flour paste (like wall paper paste) and add sand to it. You can paint this mixture on top of your wall and the result will be a sandy textured surface that will allow most paints to key onto, as well as a thinner coat of plaster.

2) Cracking. As long as the concrete blocks are stable within the wall system, it should not affect your wall finish. If the mortar between the blocks shows signs of cracking due to movement of the building over time, or seasonal shifts (freeze and thaw cycles for example) then you would want to employ more drastic measures to make sure that you do not have cracking coming through your new earth plaster or paint. I suggest covering the wall with some kind of material that will act as a bridge. In the conventional world, cement stucco is applied over a stucco mesh. This mesh gives a 'keying' system for the stucco and also provides a fabric throughout the stucco that will assist to prevent cracking. You could do the same with something like burlap in a more natural setting. It is important for the burlap (or whatever material you may use) to be firmly connected to the wall so it will not separate from the wall or sag. You would then apply your plaster over this material and this should help to prevent any cracks from tracking through to the surface. Have fun 'naturalizing' your home!

Q: I have read a little about pourable limestone, and sandstone. This is a cementious product that yields a limestone or sandstone like finished material. Do you have a mix design that I can try out?

A: (Kelly) I don't know about pourable sandstone, but limestone can basically be reconstituted from common lime products available at building supply stores. Hydrated lime is the safest to work with, since the quick lime will "boil" when water is added. Lime is commonly used both as a component of plaster and mortar, and also as render in its own right. It takes quite a while to cure, and in fact lime continues to get harder over years as it absorbs the CO2 from the air. Without the addition of sand, the lime will shrink a great deal as it dries. To find out more about the uses and formulas for lime products, I suggest that you browse http://www.buildinglime.org/  .

Q: Is it safe to use to use fresh cut untreated red cedar I have harvested off my land in Texas to line a pantry? I am concerned that I may bring termites or some other type of wood eating insect into my new home. Is this a valid concern?

A: (Kelly) Red Cedar is one of the few species of wood where this is definitely not of concern; cedar in general repels insects and rot because of its resins. Cedar chests are prized exactly because they repel insects. You might want to let the wood dry a bit before using it in your pantry.

Q: I am doing lots of research on natural building and am having a hard time finding information about what kind of mortar I should use. This might actually be an unusual place to look because the houses I am building are a little on the small scale. I'm making miniature houses and want to make them as natural as possible to the point where I'm not even using nails to put them together. I got a lot of inspiration from this site that I'm going use bamboo and most of the designs with thatched roof. I'll be using various stones and don't know what I should use to make it all stick together. I don't want to go the traditional route of miniature building with using resins, or cold casting anything because after doing more research I found out that it's really plastic and that's not what I want to use. I want to use something that is good for the environment, not toxic to me and can be left outside in the garden. Any suggestions would be wonderful because I am at a standstill.

A: If I were in your position I would look to the historical buildings before people were using cement
based products as mortar for stone. Lime has been one of the most common building materials used for centuries. Lime is a natural material-calcium carbonate. You can make a mortar using lime putty and aggregate. Lime can vary depending upon your location, therefore, you should do some research on the lime available in your area.  Although lime has been used for mortar, plasters and the like for centuries, it is important to understand how to work safely with this material. Lime is caustic due to it's high alkalinity, therefore, you need to take precautions when working with it (gloves, long sleeves, eye protection, vinegar to neutralize it in the case of skin contact). Lime takes much longer to 'cure' than cement, and therefore patience is a virtue in our modern world when working with lime. However, lime is not as brittle as cement and ultimately will give you a less brittle product.

Q: Do you think clay can be used as well? That doesn't need to be fired and "weatherproof"?

A: Yes, you may be able to use clay. It may depend on your climate. In the southwest I have seen many life sized buildings with stone foundations mortared together with clay. Since there is no danger for human inhabitants in your tiny buildings, clay may work well. You would want to have some sticky clay to aid in adhesion. I would probably paint the stones with a clay slip (clay mixed with water to use as a glue) first before embedding them in the clay mortar. Build the foundation with the mission of only using the clay to fill in the gaps. It will be stronger if the stones are doing all the work (dry stack method). If the weather is a concern in your area, you could oil the mud mortar after it is dry, and finish it off with a coat of melted beeswax to prevent water damage. Oiling the stones also beautifies them.

C: (Owen Geiger) You'll see low-fired brick in use throughout Thailand.  It seems to be the number one preferred building method in Thailand and other SE Asian countries.  Unlike high-fired brick which uses a lot of energy, low-fired brick uses a modest amount of energy.  They're produced at the village level using very simple techniques that have been used for over 4,000 years.  Their main advantage is durability in wet, humid environments.  Two sizes are typically available.  The larger size is more cost effective and requires less mortar.  You could use lime mortar.  Plaster is not necessary, although obviously it will help protect the wall.

Q: Is it possible to place earthen plaster over Tyvek?

A: It is possible to put earthen plaster over Tyvek but you would need something to make sure it adheres to the Tyvek. I am assuming this is an exterior application, and that you are doing this purely for aesthetics. The plaster would need to have an adequate binder to make it stick to to the Tyvek. In addition, and more commonly, you would need to wire the building and use spacers, as if you were applying cement stucco. I have done this on occasion and the main concern is making sure the plaster is pushed through the chicken wire so it becomes embedded in the body of the plaster. The Tyvek at this point is simply behind this new layer. It is important to consider what is behind the Tyvek. Whatever is behind the Tyvek needs to be solid so that the plaster has a solid backing (the chicken wire and spacers adhere this to the material behind) and cannot move, pull away, or crack due to an spongy, or moving substrate.

Q: I have a two car garage that I am excited about turning into an earthen apartment. It has standard construction 2x4 stud framing, truss roof and T1-11 siding. My plans at this point is to do Leichtlehm within the stud walls voids for insulation, then do a lathe and plaster using earthen plaster. I live in Portland Oregon area and had a little concern about moisture passage due to the T1-11 walls. Have you ever heard of anyone doing something like this or maybe you have some experience? I just don't want the walls to build up moisture in them and well we know what happens after that - I get very sad. Oh, I am also adding some Borax to the Leichtlehm as an added measure for pests, not that this is going to effect the moisture passage.

A: I haven't heard of anyone doing what you are planning to do. However, I have asked about this years ago. I built a Light Straw Clay house in Coastal Northern California. At some point in the building process I had a talk with Bill Steen of The Canelo Project. He suggested that if we had wanted to do board and batten on the exterior that he would recommend leaving an air space between the straw/clay wall and the wood. That way, moisture that may condense wouldn't be sitting on the straw when it did.

I would suggest getting in touch with EcoNest the LSC specialists in New Mexico and ask them if anyone has done this, and what they suggest. Robert or Paul (Baker) LaPorteare experts in this field. www.econesthomes.com

By the way, I don't use lathe over straw when I plaster. It isn't necessary with earth plaster. Simply bridge all dissimilar materials (wooden studs and the like) with some kind of material. I use burlap and clay slip (clay slip both sides, staple into studs, and secure into straw before plastering). If I am bridging a 2x4 I cut my burlap 5.5" wide for example. The earth plaster will stick to all of this easily if your mix a good and your apply it well (good adhesion methods!).

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I specifically disclaim any warranty, either expressed or implied, concerning the information on these pages. Neither I nor any of the advisor/consultants associated with this site will have liability for loss, damage, or injury, resulting from the use of any information found on this, or any other page at this site. Kelly Hart, Hartworks, Inc.


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