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Hello,
We recently waterproofed the lower level of the house as its had some water ingress issues in the past. The product used was WPA 100. We were advised by the waterproofer that we can render over it. I'm wondering if any particular care should be taken when rendering over waterproofing membrane and if there's any recommended products to use.
Welcome to the Bunnings Workshop community @jaymars. It's terrific to have you join us, and many thanks for your question about render.
As I am not familiar with the waterproofing product used, I am unable to verify compatibility with our renders. It is important to be a little cautious before proceeding. While it is common for some waterproofing membranes to be renderable, the exact suitability, preparation requirements, and allowable render types are always dictated by the membrane manufacturer.
The safest first step is to contact the manufacturer of the product, or go back to the waterproofer who applied it, and ask specifically whether cement-based renders are approved over the membrane and whether any primers, bonding coats, or mesh reinforcement are required. Some membranes need a specific render system, while others only allow lightweight or flexible coatings to avoid cracking or delamination.
From a general application point of view, care is definitely needed when rendering over any membrane. Waterproofing layers can be damaged or punctured if heavy pressure is applied with the sharp edge of a steel trowel. A lighter hand, correct mix consistency, and avoiding aggressive trowelling is important to prevent compromising the waterproofing.
Once you have confirmation from the membrane manufacturer that rendering is acceptable, we can then help recommend a suitable product. A polymer-modified render such as a PM render may be appropriate in many situations, but that recommendation can only be made once compatibility is confirmed. Without that confirmation, it would be guesswork and could potentially void warranties or lead to failure down the track.
Please let me know if you have any questions.
Mitchell
