Civil Engineering Reference
In-Depth Information
11
Render for straw bale walls
Earthen render
The basic ingredients of earthen render
The simplest earthen render would be made up of a mixture of clay and sand. There are a
range of things that might be added to this for aesthetic appeal and function.
In our home in Heathcote the render for the internal walls is made up of clay, sand and
chaff. We used white sand with white clay, so the chaff has given us a natural oatmeal
appearance, which is very soft to the eye. It warrants mentioning at this point that earthen
render is much more workable than cement render. To apply 10 mm of cement render is a
challenge, as it is inclined to slump and come away from the wall. The application of 40 or
50 mm of earthen render is possible as it is less inclined to slump, as it is quite sticky. The
application of render in multiple thin layers is preferable to the application of a thick layer,
which is much more likely to crack as it dries. I shall cover this in more detail shortly.
The third and final coat of render at Heathcote is a mixture of white sand, white clay
and a little lime. The lime was added to increase the render's resistance to the weather and
to give us a whiter white on the outside walls, for the appearance we were after without
having to go to the trouble of white washing.
There are numerous other additives that can be put into the render including linseed
oil, cooked flour glue, cactus juice and cement to name but a few. The only one that I
would definitely advise against would be the inclusion of cement. I would not personally
consider render with the inclusion of any cement to be an earthen render. The inclusion
of cooked flour glue and linseed oil is primarily to reduce dust at the surface of the wall,
which I might add is not a problem in our home. While the inclusion of linseed oil can
help with dust, if included in the wrong ratios it can cause delaminating of the third coat
of render from the second. Therefore, I must emphasise that the only solution is: test, test,
test and test before you even think about putting it on your walls.
