Civil Engineering Reference
In-Depth Information
associated with water penetration, this would lead to the breakdown of the straw
surrounding the power point, and reduction of thermal resistance in that area of the wall.
You can purchase waterproof covers to go over standard power points and switches. This
would be a better option for external fittings, as they are mounted on the wall box
thereby providing a much stronger connection to the wall.
Strengthening the junction of the render and wall mounting box
The greater the strength of the render around the power outlet and the connection of the
render to the outlet, the better. I previously suggested that the junction of render to
timber would benefit from a coating of sand and glue to the timber. The same applies for
power outlets.
Applying a mixture of sand glue
Applying a mixture of coarse sand and adhesive to the outside of the mounting box
where the render will contact the mounting box will dramatically increase the strength of
the junction of the render to the wall mounting box. You could use construction adhesive
or Bondcrete®, however I doubt that a cooked-flour based adhesive is going to hold onto
the nonporous surface of the wall box.
The coating of sand on the wall box will provide a key for the render to lock into and
add to the security of the wall box in the wall. Earthen render alone, while being quite
strong, is not capable of withstanding too much abuse. For this reason, we apply a strong
cob around the power outlet to increase its strength. Apply the first coat of render
ensuring that the mix is worked well into the straw rather than to coat the surface of the
straw. Use the palm of your hand to force the render up into the straw. The straw is quite
sharp so you will probably need to wear rubber gloves during this process.
Using cob to increase strength around the electrical box
When the first coat of render is completely dry, apply cob to the area around the electrical
wall mount box to increase the strength of the render. For details on cob, see Chapter 11.
Wet the surface of the first coat of render and then apply the cob mix to the bales around
the outlet in a circular motion so the outlet is encircled with the straw of the cob. It is
important that there are no air gaps between the outside of the wall box and the cob.
Build the cob up around the wall box to within 10 mm of the face of the box. The
build up should ramp back down across the wall for approximately 150 mm out from the
wall box. When dry this fibrous material will strengthen the surface of the wall around
the outlet much the same way as fibreglass fibre strengthens the hull of a boat. Not only
will the wall be stronger in this area, but also the adhesive sand mix applied to the sides of
the wall box will provide a good bond to the strengthened wall.
The hole in the rear of the box where the cables enter the box should be sealed with
silicone to prevent air flow and moisture penetration.
Electrical outlets in rendered timber framed walls
It is possible to have a rendered finish on timber framed walls. Timber framed walls to be
rendered are referred to as Kram
©
walls, which are made up of a timber frame, wire
netting fixed to the faces of the timber framing and straw tightly packed into the cavity
