New to Forum - Tiling on wooden floors with UFH

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Barry bp

Hello to everyone. My name is Barry. I have been a tiler in Bournemouth for 28 years - how tiling has changed in my time. I now specialise in complete bathroom installations. When not working with other tilers or a company you become a little insular and I am not sure that I am keeping up with the changes. I use A & C Dunkley to buy my adhesive and grout - they used to stock Bal, now it is Bostick or Mapei. I use OPF on all wall tiling - never had a problem and I'm comfortable using the same product. When we (the plumber who works with me) install a bathroom we always remove existing floor, so we can check the condition of old pipes, remove as necessary, layout new pipes as required. I also plain bows and high points out of joists then screw 18mm WPB plywood to joists. If floor is not level enough I use FA600 latex. Used to use Bal fast flex (very messy). Now use Mapie S2Quick then Mapei Ultracolour grout, silicon round edges to wall tiles. Not had a problem doing this so far.

If customer wants UFH I lay this on plywood, latex again with FA600, Mapei S2Quick, Ultra Colour Grout. I've had my first problem - the bathroom is about 12m2. About 150mm into doorway is a joist, this is where the plywood meets existing floorboards. The tiles are not porcelain, seem to have a hard glaze and soft biscuit - the UFH has created lateral movement in the plywood and the tiles have cracked along joint. Also around the edges in two places they have butted too tight to the wall obviously from expansion and damaged 3 or 4 wall tiles. I feel I should be using a decoupling mat or Wedi Board over plywood. Do I still lay UFH to ply, latex, then lay mat because Wedi Board would be too insulating? Or do I lay ply Wedi Board UFH latex? Which is best? Around perimeter do I need to be allowing some kind of expansion gap? Should I leave bottom wall tile, tile floor, then tile wall to floor? Also when I lay wetdecs I run UFH in this area. I like to think it dries quickly. I'm now concerned about the edges with any expansion. Can someone please bring me up-to-date. Sorry mssg is so long. Barry
 
Hello Barry and welcome..

Your prep is good but once you introduce lateral expansion/heat to a substrate that already expands and contracts, then this is where an uncoupling membrane comes in handy..

The plywood can cause cracking at the boards joints if this butted together, so it is wise to leave expansion gaps between the boards to stop the lateral stress from heaving the boards and thus cracking/debonding tiles.

A perimeter joint is always advisable and 3mm at least would be desired around the full perimeter .. but leaving the bottom row out on the wall tiles allows a wider perimeter joint to be used and then insert bottom tile over the floor tile allowing Lateral expansion of the floor to either a siliconed joint or just an air joint and wall and floor transition joint sealed.

It is just basicly allowing for the floor to expand and contract with minimal stress...
 
:welcome:Barry.

I used to use Dunkley when I was in Bournemouth in the early 70's.

To keep up with the changes in our industry the decoupling membranes seem to be the way forward for all plywood floors IMO.

Look forward to your input on what is the Best Tilers Forum.
 
Thanks Dave, what do you think about Mapei S2Quick? What would you recommend for plywood and UFH and does the uncoupling membrane affect the efficiency of the UFH?
Regards Barry
 

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