I am about to lay marble floor tiles in my bathroom and would appreciate some advice. Currently chipboard panels over joists.

Current thinking:

- either replace chipboard with 25mm WBP ply (and suitable noggin support) or overlay 18mm WBP ply
Any advice on better option? 18mm seems easier but will raise floor height

- 6mm insulation board
- UFH mat
- Adhesive, Mapei Keraflex maxi. Is S1 sufficient or should I use additive to make it S2?
- Tile

Any thoughts on this approach?

Thanks

Welcome along to TF. If this were a job of mine I would,

1) Remove chipboard and replace with 18mm WBP (add extra noggins also) screwed to joists
2) Over board with cement board (hardibacker or similar) stuck to ply with SPF and screwed every 200mm
3) Fix a decoupling membrane, again with SPF
4) Tile using SPF

6mm square notch trowel for the cement boards and membrane, 10/12mm round notch for the tiles.

Sorry, forgot about the UFH. Stage 2, use 6mm insulation boards then fit UFH and SLC over it.

Thanks for the advice. Is SLC really necessary? Tiling an upstairs bathroom and concerned SLC seeps through floor onto ceiling below
How do I seal insulation boards so SLC doesn't drip down below?
Also do I need to leave an expansion gap around edge of ply/insulation board/ slc?
(I know I need to leave a gap around the tile edge)
Any comments gratefully received

Thanks for the advice.

Is SLC necessary? Tiling an upstairs bathroom and am afraid of SLC seeping through insulation board edges and onto ceiling below. How can I seal the insulation boards to stop this happening?

Also, do I need to leave an expansion gap around the edge of the room for the ply/insulation boards / SLC?
(I am aware that the tiles need an expansion gap).

Any comments gratefully received.

slc is necessary to ensure cables are fully covered and to prevent damage whilst tiling. leave an expansion joint between the boards and around the perimiter. i use aluminium tape around to prevent seepage

Originally Posted by always-diying

Thanks for the advice.

Is SLC necessary? Tiling an upstairs bathroom and am afraid of SLC seeping through insulation board edges and onto ceiling below. How can I seal the insulation boards to stop this happening?

Also, do I need to leave an expansion gap around the edge of the room for the ply/insulation boards / SLC?
(I am aware that the tiles need an expansion gap).

Any comments gratefully received.

Use some silicone to stop slc seeping through joints if your worried. SLC is used to protect the wires from being damaged during tile installation. yes leave a expansion joint around the edges.