Light straw-clay (or straw-clay slip) refers to a wall making technique that involves filling in the space between wall posts with compacted clay-covered straw. The wall is then covered with plaster, creating a durable, aesthetically pleasing wall that provides insulation and is constructed entirely from non-toxic materials. There are many advantages to using straw-clay, including the fact that it is easily learned by beginners, making it ideal for the owner-builder and the do-it-yourself home renovator.
Choosing and Preparing a Wall for Straw-Clay Infill
Light straw-clay can be used to fill in the space between two wall posts. To prepare a space to receive straw-clay infill, begin by removing any debris in the space. If rebuilding an existing wall in a renovation, this means removing all drywall and insulation so that only the posts or studs remain. A straw-clay wall can be built on the subfloor for interior walls, or directly on a stem wall, foundation or a beam for exterior walls. If building onto a foundation or stem wall, a moisture barrier may be necessary to prevent rising damp.
Tools and Materials Needed for Light Straw-Clay Infill
The materials required for this project are few, but they should be assembled before beginning construction to allow for efficient work.
- Two or more boards, slightly longer than the space between two posts, to hold the straw in place while it is being compacted
- Small diameter branches or boards cut to the length between posts, to be tacked between the posts to provide support to the straw-clay
- Screws and an electric driver or a hammer and nails
- A wheelbarrow or large bucket and tarp for mixing the straw-clay
- Straw, not contaminated with mold or insects
- Clay soil
- Water
How To Build a Straw-Clay Infill Wall
Once the site has been prepared and the tools and materials have been assembled, construction of the straw-clay slip wall can begin.
- Build the frames by attaching boards to the outside of the posts. The first boards should be flush to the floor, foundation or stem wall and should rise a total of about two feet. Any boards can be used for this purpose and small spaces between the boards is acceptable. If nailin
- Fill a large bucket or wheelbarrow about half-full with water. Begin adding clay soil, bit by bit, mixing well, until a suspension about the consistency of a milkshake forms. A hand dipped in the mixture should come out evenly coated with clay.
- If using a wheelbarrow to mix, add the straw and mix to coat thoroughly. If using a tarp and a bucket, begin by tossing some straw onto the center of the tarp and splashing some of the clay mixture on top. Toss the straw to coat (if using a pitchfork for this, avoid poking holes in the tarp).
- Once the straw has been evenly coated, grad a large handful and stuff it into the space between the frames. Compact the straw, trying to fill the corners well, then add more straw, compacting each time, until the top of the frame has been reached.
- To continue building the wall, simply remove the frames and replace them directly above the finished portion of the wall. Proceed in this manner until the top of the wall has been finished. The last batch of straw may be added from one side, and the final board screwed down after the space has been stuffed to ensure that it is well compacted.
- Attach the small supporting branches or boards to the posts. Every few feet, carefully nail or screw a horizontal board to the inside of each post. One branch ever few feet will suffice. The end result should look something like a ladder.
After the straw-clay wall has had a few days to dry, holes can be filled and the wall evened out with one more coat of straw-clay slip. For this coat, roughly chop the straw and blend with a thicker mixture of clay soil and water. Apply this mixture to the finished wall by hand, pressing hard to fill in spaces and create a smoother finish. Once this coat has dried, the wall can be finished with one or more coats of homemade earthen plaster or commercial plaster.
Sara Yoshihara - Sara Yoshihara lives and works in rural Japan where she and her family have a small no-spray rice and vegetable farm and an artisan ...
