Dashing Information – Preparing Surfaces for Rendering

Make sure the surface is clean & solid

Appropriate surface preparation is vital for sound trouble free rendering. Examine all surfaces carefully to determine what if any preparation is needed.

If an area is affected by moss or algae ensure it is removed completely and prevent further growth by killing the spores.

A hammer or tap test can be used to identify areas of loose, hollow or spalling material, defective areas sound dull.

Clean surface with non-metallic brush

Backgrounds to be rendered should be examined for contamination, deterioration, surface roughness, suction and strength. Dust and contamination such as residues of concrete release agents, gypsum plaster, paint, other coatings, organic growth, salts and efflorescence should be removed prior to rendering. Salts and efflorescence should be removed by dry brushing (non-metallic bristles). Other special precautions may need to be taken if this removal is not achievable.

The line and flatness of the background should also be assessed to determine if the render can be applied to a uniform thickness or if dubbing out is required. The background should be reasonably dry and free of frost, with a temperature of +5 °C or above at the time of rendering. If the suction is very high, low or uneven the use of a preparatory treatment, metal lathing, or special factory made render should be considered as part of the design.

It is important for the wall not to be too wet at the time of rendering. Walls that have recently been exposed to heavy rain should be allowed to dry out sufficiently before rendering is attempted. Do not attempt to apply render if any of the materials to be used are frozen or if there is a risk of frost damage before the render has taken an initial set. Do not apply in full sun as normal curing is impossible and fast drying will occur.

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