Civil Engineering Reference
In-Depth Information
of the straw smoothed off as much as possible. When using a render pump to apply the
render, the render hits the wall with some force, giving penetration into the surface of the
bales. The render still has to be spread evenly on the surface of the bales, so why not make
just a little extra effort and guarantee a solid fixing by forcing it further into the bales
while you spread it.
Second coat (infill coat)
The first coat of render should be completely dry before applying the second coat. When
dry, you will notice that the first coat of render has cracked, but do not be concerned. The
cracks will actually help the second coat of render adhere to the first, as the render is
keyed into the cracks. As long as the first coat is not crumbly, you are fine.
The second coat of render
Again, the surface of the wall is to be sprayed with water prior to the application of the
second coat of render. Even when using the render pump, we still spray the wall prior to
application of the second coat of render. When the wall is not wet prior to the application
of the next coat of render, delaminating is likely (see Figure 11.1). This coat of render will
be used to form the final shape that you want for your wall. While we call this the second
coat, it might well be called the second coat with parts A, B, C, D, etc. as it is often
necessary to apply additional layers to form the shape you desire. This shape can also be
attained with the use of cob, which I shall discuss shortly.
Figure 11.1
Delaminating of the third coat of render due to incorrect preparation
The second coat of render will be applied with your hands, a trowel or a render
pump. Once on the wall, the render will be smoothed out with a trowel. The longer the
trowel, the flatter the surface you will achieve. If you are after an almost flat surface you
might choose to use a screed across the wall. Screeds vary in length, but you will find a 1.2
metre screed is more than most people can handle. If using a screed it might be necessary
