Though I’ve got plenty to learn with Straw, I can use this post to collate any thoughts on Straw Bale as a building material and any dos/don’ts that I can think of.
As long as it’s done properly, there is no reason why you can’t build yourself a circular straw bale building. Shaping bales is reasonably easy with the right tools, and we even resorted to chainsaws to cut notches into the bales. I found as a buliding material, it can be quite forgiving with regards to accuracy (though thats not an excuse to be inaccurate!) so playing around with the shape and edges is good fun. Just make sure they are tied well, and packed in so as not to be too loose in a wall. You have to remember that over time, they may settle, so a tightly packed bale is of the upmost importance.
To withstand the weather, you would assume that bales need to be plastered as soon as they are put on. I was surprised to find that this is not the case. While is not necessarily advisable to leave bales uncovered, as long as there is a decent roof covering, they should be able to withstand weather, given time to dry out. Water does not soak in, unless it ends up at the top of the bale, with gravity pulling it in. The photo below (taken in March) shows a bale wall that was built in September, and was still in reasonably good shape despite going through the winter. There had been development of some patches of damp, especially above the door frame, where the fold of plastic had caught water and allowed the straw to sit in it. Also, the lack of an overhanging roof meant that the walls were not as covered as they should have been, ideally.
When plastering the walls on the straw bale course, we used chicken wire to cover the bales, and assist in the plastering. There was a split with regards to if this was a good or a bad thing. You can see in the photo below the chicken wire.
For the first course, it certainly made plastering easier, and probably would result in the use of less plaster. However, I thought that it might result in the plaster not tying itself into the bales quite as well, and though it is more effort to get that first course of plaster into the straw, the knowledge that it is mixed directly into a bale, and not with chicken wire would be better for me. In areas where the chicken wire strayed from the bale, I felt like the plaster might end up leaving a hollow part of wall, which could result in potential long term weakness. (This was addressed by pinning the chicken wire into the bales at these points, but I remain unconvinced!)
Plastering – Clay vs Lime
to be continued.