Hi all--
First of all--thanks so much to everyone who has contributed to this thread--we really appreciate the advice which has been given. I have been back through the posts, and would like to sum up the advice as to where we go from here. I have highlighted areas where I'm note sure of myself--grateful for any comments--this is what we'll go back to the builder with.
1. The whole floor will need to come up, down to the chipboard.
2. On top of the chipboard--should we lay backer board AND decoupler, or just decoupler? I understand that if we do use backer board, it needs gluing AND screwing to the joists. DavieA suggested doing away with backer board, and replacing with ply (what thickness?), then decoupler. If we did that, I presume the ply should also be glued and screwed. What's best?
3. On top of the decoupler--travertine tiles need 'back-buttering' with the right adhesive--keraflex was mentioned (again by DavieA--thanks very much), and definitely no dotting and dabbing to be used. Adhesive must be pale coloured or it will seep through and look as though the floor has measles.:smilewinkgrin:
4. Grout--any special tips here?
5. Clean and seal the tiles.
6. 2 weeks after the tiles have been laid, the UFH needs testing at 5 degree intervals up to maximum heat.
7. Cross fingers.:lol:
Thanks again for your help so far.