The trouble with having help in to do plaster work is that sometimes it doesn’t get done right. As straw bales wall settle, they sometimes shift. If you’ve left a hole–of any size–the plaster is going to crack, and presto, you now can see the hole that was formerly hidden.
This cropped up in the lodge just recently. The good news is that earth plaster and alis are very easy to repair.
First step in the repair work to actually open out the whole and remove any loose plaster. You want to find out the full extent of what needs repairing (if you put plaster into a crack, it might just crack more, but if you widen it out and then make the repairs, it’s going to stay put).
Once you have all the crumbling plaster out, now it’s time to mix up some new plaster. Ah–but first, time to fill the hole!
Holes are always bad with plaster–an empty gap means the plaster has nothing to hold onto. So you want to give the plaster a solid backing. In gaps between bales or corners, this sometimes means you need to fill the hole. Loose straw won’t do the trick. So this is where burlap becomes your best friend.
Make a clay slip (sift clay and pour it into water, adding the clay until you have the consistency of a thick milkshake). Cut up burlap (and you can use recycled coffee bean sacks for this, purchased from Online Fabrics) into strips. Dip the burlap into the clay slip and start pressing them into the hole until you have a smooth, flat surface. DO NOT use metal–clay and metal don’t get along very well (they expand and contract at different rates).
Let the burlap dry anywhere from a half hour or an hour. During this time you can make up new plaster (use screened/sifted clay and sand, with a ratio of about 2 parts sand to 1 part clay–but depending on the clay you may need more sand, and use sharp sand). Add water enough to make the clay mold together and not slop into a mess in your hand. I also like to add 1 quart wheat paste to every gallon of water. (Wheat paste is made by adding 1 cup of flour to 1 cup of cold water, mixing well, and then add that mix to 3 cups boiling water.)
Once you have your plaster ready smooth it in–the burlap will readily take the plaster. Smooth in the plaster–you can use hands or a wood trowel works very well to give you a nice smooth plaster.
Again, let this dry. You can dry overnight or for an hour or two. The plaster does not have to be totally dry, but you do want it to be set so that the alis or finish coat goes on top and does not mix itself in with the plaster coat below.
While the plaster is drying, mix up your alis (and we have other posts on this site for different recipes). In this case, we needed a white alis and so we used the Kaolin clay–but we’ve also been experimenting with different natural pigments. A new post is coming on this!
Cover the plaster with the alis. To do this, paint it on with a brush–it should be thin enough to allow that, but thick enough to cover the plaster. Smooth and polish with a damp sponge to remove all brush marks.
The repair is all done, and can be finished in only an hour or two (depending on how long it takes to dry each stage). And best of all clean up is easy for hands, buckets, brushes and sponges with some fresh water.