I'm installing UFH. Current scenario:

- 9mm WPB Ply screwed down @ 150mm centres onto wooden floorboards
- 10mm Marmox insulation boards (1250 x 600mm)
- UFH cable
- Tiles

Question is for installation of the Marmox onto the ply. Would you use tiling adhesive (Granfix flexible rapidset 3mm bed) with screw in each corner? Or can I just screw down insulation boards @ 300mm centres and forget about the hassle of adhesive? Marmox website suggests either option.

For the adhesive option, does the ply need to be primed? If so, is PVA glue/water mix ok?

Thanks

Hi Im looking to do the same thing as you.

I would love to know if you have completed the floor and what method you used.

Hi, Marmox screwed to the ply and floorboards will be fine, just use stainless steels screws and washers, or marmox supplied screws and washers, (use the correct length to avoid any plumbing disasters)
You can use a powdered cement based flexi tile adhesive also, if you choose this route you dont normally prime the ply but follow the adhesive manufacturers guidelines.

Gary
plumbingsolutions@ntlworld.com

Hi thanks Gary

Any recommendations on the adhesive front? I can get BAL near me pretty easily. Which one is the best to use on the underside of the backer board?

If you are going to stick it down i would use Bal SPF

screwing will be sufficient though.

You should always use adhesive to stick the boards down and screw them as well..

definitely NO to the pva tilingvirgin