How to prevent render cracking: Advice for applicators

To avoid the risk of cracking, it is essential that certain considerations are taken into account prior to and during the application of render. This section, aimed at the monocouche applicator, focuses on good practice when preparing a substrate and applying the monocouche render.

Suction control

Good porosity of the substrate is essential for the render to achieve a good bond. However, if the substrate is too porous it will not allow the render to hydrate sufficiently and if it is too little there will not be a good bond. If either of these situations occur the following best practice should be followed:

  • High porosity – this is particularly the case with low density blocks. The substrate should be lightly sprayed with a fine mist of clean water evenly before the render is applied. Saturation should be avoided as this will cause excessive shrinkage.
  • Low porosity – this is particularly the case with concrete or brickwork. weberend aid should be used to provide a controlled level of  porosity and a mechanical key.

Movement joints

Any movement joint within the substrate must be followed through the render to ensure that cracking is prevented at that point. This is also the case for compression joints.

Using Weber Standard Mesh Cloth

The ability of the render to distribute and resist stresses can be enhanced by the inclusion of Weber Standard Mesh Cloth. This should be applied at typical stress points in the substrate, for example to prevent cracks in render around windows and doors, and at junctions of dissimilar materials (e.g. ring beams). Mesh should also be used around crack inducers such as weep holes.

The mesh should be cut into strips that extend past the junction or point of weakness by approx. 500mm and pressed evenly into the freshly applied render using a trowel or spatula, ensuring no contact with the substrate. A further layer of render should then be applied to encapsulate the mesh.

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