Render finishes are often the final and most important element in the building process as they define the overall aesthetics of the structure. All too often they are considered as a cover-up for other construction bad practice and poor alignment. Sometimes renders are required to be applied over inappropriate surfaces. So be sure to know what's a suitable background to render over.
Painted or coated substrates
Painted or coated substrates have a low suction and often have a poor key for render finishes. Additionally, the bond strength of the coating to the substrate is usually too low to carry the weight of a render coat.
Substrates out of plane
Construction tolerances or dimensional accuracy of blockwork and concrete is often at odds with the accuracy needed for good rendering. Steps in the surface or excessively thick areas of render can give rise to potential cracking or shading problems.
Dissimilar substrate materials
Existing cracking or the potential for differential movement arising from dissimilar substrate materials can transfer stress into a new render, resulting in cracking.
Renders applied to substrates that are too weak or to those with weak surfaces are likely to fail along the plane of the interface as the surface of the substrate itself fails.
Some info for our customers on knowing what backgrounds are suitable to render over. We will release a blog in a few few days with solutions getting round these problems before getting an exterior team in to complete work on your house.