Carpentry & Joinery

Overboarding chipboard with ply - Best practice?

Anonymous user 03/03/2024 - 3.20 PM

I would like to know the best practice for securing the tiling substrate/subfloor when overboarding chipboard with ply in an en-suite bathroom. My builders have laid 22mm T&G chipboard over the joists. Whilst they have glued the joins, I don’t think they have glued the boards to the joists. The builder will now lay 12mm ply onto the chipboard and they intend on securing the ply using a long screw which will go through the chipboard and into the joist. The tiler will then apply a decoupling membrane like ditra may to tile on to. My question is, should the chipboard be secured with screws first, before securing the ply, or is one long scre sufficient to secure both layers. Additionally, should the ply be glued and screwed, or just screwed. I saw on a forum somewhere that the ply should only be secured to the layer below, but it’s unclear whether that applies when the chipboard subfloor is not secured with screws. I don’t want to have any movement later down the line, so just wondering if someone can tell me the best bractice. Overboard with one screw, screw both, screw then glue and screw etc.