It may be time to think about preventing this plaster and render cracking before it happens, if only to avoid annoying repair jobs post completion.
Why does plaster and render crack?
As frozen in place as any building looks, they are constantly moving. There are a variety of forces that pass through any construction. First it could be shrinkage that comes when plaster and render dries, or it could be weather erosion, or moisture movement, or thermal expansion that causes expansion and then shrinkage. In short, any traditional plaster or render, without proper supporting materials will always crack. Sometimes these cracks will be insignificant enough to be covered with paint, at other times they will look disastrous, suggesting structural insecurity.
How to prevent cracks in plaster and render?
The first prevention tip is stopping the plaster or render from drying too quickly. This means avoiding plastering and rendering in direct sunlight or where there is a strong wind. The premium time for plastering or rendering in the warmer months is early in the morning, as it is less humid at this time of day.
You should also make sure the wall being plastered is coated with a watered down PVA glue, so that the brickwork does not absorb the water in the plaster.
However, most cracking will signify an error in the choice of materials used. Therefore, material selection is crucial. You should not use sand that lacks fine material and if it does then you should add some lime into the cement. However, one sure way to prevent shrinkage cracks particularly is with the use of fibres in the mix, which will take some of the force of the movement through the material.
How do fibres prevent concrete from cracking?
Siteworx Plaster and Render Fibres can be used in most types of render, as well as in base coat and finishing plaster, including lime-based plasters. These 3mm polypropylene monofilament plaster and render fibres are designed to be used to minimise shrinkage and cracking.
This is not a new technique; we are not recommending a revolution in thinking. It used to be that builders of old would use horsehair to achieve the same effect. Now, however, we use these synthetic fibres to bind the material together, while absorbing some of the tension created when it dries, and throughout the life of the build, as the construction naturally moves with heat and moisture.
You can get our Siteworx plaster and render fibres in 200g bags, and it can be stirred into your mixture of plaster or render before application. It couldn’t be simpler really – and will ensure the perfect finish.
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