Civil Engineering Reference
In-Depth Information
does not come cheap, but it was at least a solution to what was a rather amusing situation.
Mind you, I know many owner-builders who would have not been amused at all. Soon
after the baking of the render they moved out of the tent, which only days after dropped
its side walls as the material broke down, and they haven't looked back since.
Mixing of cob
Cob is a mixture of render and straw. The render used for the first coat is ideal, although
it may be necessary for it to be somewhat more liquid as the clay mix should coat all of
the straw. Cob can be mixed either in a barrow using your hands to work the render
through the straw or in a cement mixer. While cob is predominantly straw, there must be
sufficient render in the mix to facilitate adhesion to the wall and smoothing of the surface
straw back onto the wall.
Alternatives to hand application of render
The time involved in hand rendering a straw bale house will always be the same. The only
way to reduce the time spent in rendering is to change the approach, however this often
comes down to budgetary issues.
Length of time rendering
It took four people more than three months to hand render one owner-builder's house.
One of my owner-builders employed two people for more than three months to help him
and his wife apply the render to their house in a suburb of Melbourne. There were no
internal rendered walls, just the inside and outside of the external walls. I must admit
however, it was a house of significant size, probably close to 30 squares downstairs, which
is the area with the straw bale walls. He was somewhat amused at the speed of rendering
when the render was applied to the wall with a render pump.
Contract render companies, all labour supplied
I recently spoke to a company that does contract rendering of straw bale houses about the
cost of rendering. They informed me that when they supplied the scaffold, which is
normally minimal, and the materials and labour to apply three coats of render, the final
cost would be approximately $70 per square metre. My son's straw bale house in
Heathcote, which cost less than $22,000 (2005) to build has about 226 square metres of
straw bale walls. This does not take into consideration the internal walls of the house,
which are also rendered, only the inside and outside of the external walls. At $70 per
square metre the additional cost of having the render supplied and fitted would be
$15,800 (2005) (it would have taken three days for my son and four helpers, with a render
pump). If this fits into your budget it is a great way to go, however, for many people this
is not a viable option as the funds are simply not available.
Hiring equipment for rendering
One option is to hire a render pump with a pump operator and supply the additional
labour yourself. In 2003 we purchased a render pump from Italy which is hired out to
owner-builders with one of our operators. This significantly reduces the cost of applying
