Due to the vast number of waterproofing membranes on the market, it is the responsibility of the applicator to verify with the waterproofing coating company that a cementitious product can be applied over the selected waterproofing membrane. Additionally, if the waterproofing does not perform well due to water ingress over time, Rockcote cannot take responsibility for the failure.
It is important to note that Rockcote always recommends an adhesion test be carried out using Rockcote Keycote or *Rockcote High Adhesion Primer prior to application of subsequent renders and textures to ensure adequate adhesion to the waterproof membrane.
In general, cementitious waterproofing products are a safer option to use compared to polyurethane alternatives. However, as long as the correct preparation has been carried out, Rockcote can generally provide a system specification with Rockcote Keycote or Rockcote High Adhesion Primer as step 1.
When using a flexible waterproofing membrane, it is important to understand that render is a fairly rigid finish. Why is this important? Typically, when applying a coating system, the most flexible component should be on the outer layer in an effort to minimise cracking. If your selected waterproofing membrane has a greater than 100% elongation rate, it increases the chance of a failure in the system. One way to minimise the risk is to add mesh to the coating system, as this reinforces the render like reo does in concrete. Additionally, 1mm of a Rockcote Texture as the finish coat would provide full acrylic flexibility on the surface to help prevent micro-cracking.
Another key point to look out for is on the waterproofing product’s Technical Data Sheet in the render specification information section. Some waterproofing products are required to be broadcasted prior to the application of render; this is where clean sand is thrown into the last coat of the membrane before it is dried. This provides something for the Rockcote Keycote or Rockcote High Adhesion Primer to grab onto.
For improved adhesion on high-risk surfaces, such as polyurethane, it is very beneficial to add Rockcote Fast Bond to Rockcote Keycote at 50/50 bond to water ratio in the gauging liquid or apply Rockcote High Adhesion Primer.
*Rockcote High Adhesion Primer falls under the definition of Deemed-to-Satisfy (DTS) Provision for ancillary elements. 1.3.2 Permitted ancillary elements C1.14 (I).
