Civil Engineering Reference
In-Depth Information
the render while overcoming the lengthy process of hand rendering. The owner-builders
have their friends and family help on the day of the rendering, their task being simply to
mix the render and wheelbarrow it to the pump. The pump operator then sprays the
render onto the wall whereupon the owner-builder and his assistants simply spread it on
the wall in the desired shape.
Depending on the efficiency of the mixers and render spreaders, most houses with
upward of 400 bales can be rendered inside and out in a day. At a cost of $770 per day for
the pump and operator, this is a sizable saving considering that the house can have all
three coats applied over three days which would obviously be staggered to allow drying
time between coats. The Melbourne house that took over three months to render would
have been completed in six days using the same four people, plus my son Brad operating
the render pump.
Installation of earthen render
First or 'discovery' coat
The first coat of render is sometimes referred to as the 'discovery' coat because as it is a
relatively thin layer of render it enhances the shape of the bales as they are in the wall.
Render can be applied to the wall manually or with the use of a render pump. The first
coat is to be applied to the surface of the straw bale wall so that all the straw is coated in
render. This is not the coat of render to fill hollows or blend-in bumps. This first coat is
often wetter than the second and third coats, as this makes it easier to force the render
into the end fibres of the straw, which is the key to a stable and secure base. When
applying by hand the mix, will be drier than pump application as the wetter the mix the
more difficult it is to manage by hand.
Wetting the straw bale wall
As with rendering in conventional construction, the surface of the wall must first be wet
with a spray of water, otherwise all the moisture will be sucked out of the render by the
dry straw and delaminating will occur. When using a render pump, it is often unnecessary
to spray the wall with water before the application of the render, as the render is generally
much wetter than render applied by hand. Cement render applied to a dry brick wall will
fall off the wall within an hour or two, if not in a few minutes, however the first coat of
render on straw is unlikely to fall away until the additional weight of the following coats
of render is applied. Don't be fooled into thinking you can get away with it just because
the first coat of render is staying on the wall. The first coat is the foundation for the rest
of the render and no short cuts should be taken.
Force the first coat well into the straw
Apply the first coat of render to the wall, working it into the straw and going as deep as
possible with the palm of your hand. It is essential that you wear rubber gloves for this
process, not only to protect you from the drying effect of the render, but also to prevent
the straw cutting your hands. Once the render has been worked into the straw, smooth it
back over so that there are no deep finger lines in the render. While you are not to fill
hollows in the wall with this coat, all the straw should be coated in render and the surface
