Installing insulation boards over a Wooden Subfloor
When installing over a wooden subfloor, first use a trowel to lay a modified mortar. The boards will then need to be staggered and pressed together.
The boards should be secured with a galvanized screw and tab-less washer (making sure that the washer covers both boards but that the middle of the washer is not in the middle of the seam), one per foot. Tighten the screw washing until it is flush with the surface.
In a dry area, use an alkali fiber mesh tape between the joints. Use a modified mortar over the top. Install your heating system accordingly. In a wet area, use a polymer-based sealant and adhesive between the boards and let dry (this usually takes between 20 and 30 minutes).
Once dried, install the heating system accordingly.