Shingle Dash, Rough Cast and Stipple for Outside Walls
A shingle-dash or rough-cast finish coat can be achieved by flicking small stones or shingle on to a ‘butter’ coat.
The basic rendering coat should be scratched diagonally and the floating coat should be combed in horizontal lines. Smooth off any rough projections with a wooden float.
The floating coat should comprise one part cement to three parts of soft sand. A small quantity of plasticizer should be used in the mix, unless working in hot weather. In this case, a liquid water proofer should be added instead of the plasticizer.
The proportions are 25 per cent of waterproofer to 50kg of cement. After scratching in the horizontal lines, leave to dry for 24 hours.
The third coat is known as a ‘butter’ coat. The proportions are three parts sand to half part of cement and one part of lime. Working over a small area at a time, about 500mm2, ‘iron’ on the coat to a depth of about 6mm.
Using clean, well-washed shingle and a laying-on trowel, flick the shingle on to the butter coat. The secret is to get the shingle applied evenly. One trowel load will cover an area one third greater than the area of the trowel.
Do not pick up too much at one time as it will be difficult to flick the wrist to apply the shingle, resulting in an uneven surface. Place a dust sheet below the work to catch shingle that does not adhere so that this can be used later. Work to within 50mm of the area being treated.
Next apply a butter coat to the next 500mm2 area and apply shingle to this. When ah area of about 2m2 has been covered, use the wooden float to tap the shingle gently into the butter coat. The float should be used dry and wiped clean frequently.
Rough-casting is applied to a keyed floating coat. The mixture is made up of half a part of cement to one part of lime, to provide suction, and two parts of shingle. Pea gravel, a rounded gravel, provides a good rough-cast surface. The mixture is applied directly to the surface, again using the flicking action.
The consistency should be sloppy and can be applied directly from a bucket. Many find this an easier technique than shingle dash. Gravel applied too thickly will slide down the surface.
A variation of cement fining is a stipple finish. Lay a coat about 6mm thick on to a well-keyed float coat. Smooth down any uneven areas with a wood float and then, using a stipple brush, stipple carefully over the surface.
Another finish which offers a variation of texture is based on the same technique as cement fining. Apply a 6mm finished surface and then use a hard wire brush to make horizontal streaks on the surface. As the surface begins to harden, trowel lightly over the surface. When finished, a veining effect will be achieved.
A finish called Granosit consists of a dried material, mixed with water, and allowed to stand for 30 minutes. The float coat should be well keyed. Apply the mixture with a steel trowel to a depth of 10mm. As the surface starts to harden, using a wooden float, finish the surface with horizontal sweeps. This surface, which is water repellent, is obtainable in white and coloured finishes.
10. November 2011 by admin
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