Civil Engineering Reference
In-Depth Information
render is firm to touch but not yet too hard to mark, you will need to hatch the surface of
it. Score the face of the render with marks 1-3 mm deep to provide a key for the final coat
of render to lock onto (see Figure 11.2). It is important not to do this too soon after
rendering or the hatching will end up too deep. If the final coat of render is applied to a
wall with deep hatching you can get discolouration of the final coat of render. Not
everyone hatches the surface of the second coat of render, but if your render is of a good
recipe, it will resist the penetration of moisture and the accompanying final coat of
render. If cracks appear in the second coat of render it is again of little consequence, as
the final coat will key into them. Any large cracks should be filled prior to the application
of the final coat of render to avoid the risk of discolouration of the final coat.
Figure 11.2
Scoring (hatching) of the second coat of render provides a fixing key for the next coat of render
The third coat or finish coat
The third coat of render is the finishing coat, and should be applied with a depth of
5 mm to 10 mm to avoid shrinkage cracks. This final coat of render should only be
applied after the second coat of render, and any cob applied to the second coat of render,
are completely dry.
Applying the final coat of render
Wet down the surface of the wall to be rendered and then apply the render in the same
manner as the second coat. While it is not essential, if you use a slightly shorter trowel
than that used for the second coat of render you will find it easier to trowel the surface
