I am about to put down a ceramic tile floor in the kitchen. The floor is half concrete and half floorboards. Should I use plywood on the timber and self levelling compound on the concrete? Any suggestions gratefully received - thanks
I'm in the same boat so await any answers. I have been told by my kitchen fitter that 1/2 inch ply over the whole lot including the join between concrete and floorboards will be necessary. It will be screwed into floorboards and fixed to the concrete with panel adhesive. He also advised a water-based bitumen emulsion be painted onto the concrete first to prevent any damp coming through. I'm just concerned that the existing concrete and floorboards are very uneven in heights with the concrete varying by about 15mm in height between some spots so I hope the panel adhesive will be strong enough to "grab" onto the high spots.
You can but ideally if you can it would be best to remove exsisting floorboards and replace it with exterior plywood to the same level as the floor screed. This way you have the same floor level.
I have been told by my kitchen fitter that 1/2 inch ply over the whole lot including the join between concrete and floorboards will be necessary. It will be screwed into floorboards and fixed to the concrete with panel adhesive.
No need as there should be a dpm under the floor screed to prevent rising damp.
I'm just concerned that the existing concrete and floorboards are very uneven in heights with the concrete varying by about 15mm in height between some spots so I hope the panel adhesive will be strong enough to "grab" onto the high spots.
Without seeing the floors in questions I would normally suggest the following.
1. prime the concrete subfloor if necessary to kill and dust (the suggestion of a bitumin primer worries me, it should not be necessary as there should be an adequate d.p.m in the subfloor...otherwise it may simply prevent the levelling compound from binding properly with the subfloor.
2. Smooth the entire subfloor with a thin, 2mm coat of latex screeding compound. This is not 'self-levelling'. Almost scrape the screed along the floorboards, running it along the length of the boards, so that any gaps and depressions are filled, while the ridges remain bare. A thin wash over the concrete will again kill dust and level out bumps. If the concrete is higher than the timber then yoyu have to marry the two in at this point.
3. Lay 4 or 6mm wbp construction/exterior grade plywood over the timber floor. Lay the length of the sheets at right angles to the direction of the floorboards and nail with 1" serrated ring nail (don't go through any pipes!). If the concrete is lower than the timber floor then I would be happy to use the 4mm plywood since you don't want to raise the height of the floor any more than necessary.
4. The joint betyween the timber and concrete subfloors is always a weak point were movement may occur so its essential that the plywood bridges over this to protect the floorcovering from movement below. I normally take the plywood a few inches over onto the concrete, fixing it with a filler adhesive (gripfill or liquid nails) and weighing this down until the adhesive sets.
5. You then need a final coat of latex screed from the edge of the plywood onto the concrete to creat a level (acceptably level) floor. Don't wash screed over the plywood because you can never trust the bond completely.
I suppose you could cover the entire floor with 1/2 inch plywood, but this is expensive, you still have to screed the floors level, and your raising the height of the floor which may create steps at doorways etc. Most of all I would be concerned over fixing such a large area of plywood with adhesive and would certainly use exterior or marine plywood.