Siniat do not recommend the use of hot-applied waterproofing materials with Weather Defence^TM. You must only use cold applied waterproofing materials.

Gypsum based boards should not be subjected to temperature conditions where the surface of the board is likely to rise above 50°C, as the state of the surface and core can begin to change beyond this temperature.

Hot-melt systems can typically be applied at around 180°C, whilst these will arguably cool relatively quickly, it is beyond the limit at which we can guarantee the boards performance and durability during installation and ongoing operation of the building.

Gypsums products’ fire resistance requires the gradual dehydration (calcination) of the core of the board. Calcined gypsum on the exposed face binds to un-calcined materials retarding further dehydration –resulting in good fire resistance. If the material in the core has previously been calcined through methods of hot-melt installation, this will result in a likely decrease of fire resistance. Also, during in house testing of hot-applied waterproofing during the product’s development it was found that the board surface hydrophobicity and facia cohesion were also negatively impacted, along with the overall board flexural and rupture strengths –becoming brittle. It was also found the board surface had calcined beyond an acceptable level.

Therefore, Siniat are unable to approve hot-applied waterproofing systems for use with Weather Defence^TM– installers / contractors do so at their own risk.