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Can I tile/ lay floor directly over CosyBoard?

Yes, you can. However, we give clear directions for preparation, and these methods must be followed to maintain system efficiency. CosyBoard is a gypsum-based product, and, as any plasterer or builder will tell you, gypsum and cement don’t have the best of relationships. Therefore, before applying any cement-based product to CosyBoard, it must first be prepped with a primer.

The primer should be applied in two stages (a 3:1 mix followed by a 1:1 mix) to seal the gypsum and prevent any product reaction. As you will be laying a heated floor, we would also recommend applying a decoupling or anti-fracture membrane under the tiles – this will prevent any lateral movement when the system expands and contracts during the warm-up and cool-down phases.