UK Moisture in floor advice...please

[sparkymarky78]

Ok thankyou. Do the channels in the underside of the ditra mat direct allow moisture to flow along their length? If so does that moisture end up going to the walls?

 

[Tile Marble Granite]

The backer boards are 100% moisture proof. That floor is ready to be tiled.

Uncoupling membrane speaking: if there are 2 sheets of Ditra on the floor, you may apply a polyethylene tape on the joint. If you are worried about any moisture getting to the walls, then you can apply tape to the walls as well.

Schluter KERDI KEBA Sealing Tape - Tiling Supplies Direct

Schluter KERDI KEBA Sealing Tape is a sealing band used to seal matting and board connections/joints and wall to floor connections.

www.tilingsuppliesdirect.co.uk

 

[sparkymarky78]

The backer boards are 100% moisture proof. That floor is ready to be tiled.

Uncoupling membrane speaking: if there are 2 sheets of Ditra on the floor, you may apply a polyethylene tape on the joint. If you are worried about any moisture getting to the walls, then you can apply tape to the walls as well.

Schluter KERDI KEBA Sealing Tape - Tiling Supplies Direct

Schluter KERDI KEBA Sealing Tape is a sealing band used to seal matting and board connections/joints and wall to floor connections.

www.tilingsuppliesdirect.co.uk

Thankyou.

That's what I don't get, marmox boards are water proof yet the floor hygrometer on top of them reads 80% RH today at 20 degrees....and the Relative humidity in the floor will be even higher in winter when the floor is colder.

Tempted to spend a day, cover the shower glass and walls with protective coverings and sds up the boards and tile adhesive and start again, lay a 1200g polythene dpm on the bare slab, self level and put down new marmox boards or ditra, but as I can't get under the shower done 100% with the dpm sheet thats likely pointless/fruitless I guess

 

[sparkymarky78]

So figure your option of the ditra mat is worth a shot ontop of the boards.

Oh and just noticed there are dips in the boards/not level. Ffs

 

[Tile Marble Granite]

Is it suspended floor or concrete?

 

[sparkymarky78]

Hiya, concrete floor under the backer boards. Must be a few voids of tile adhesive under the boards. Couple of places you walk you feel the backer boards compress down a little over a small area. I've just drilled, rawl and screwed one defelction area using the large metal board washers to pull the areas down and that seems to work. Maybe I can do that in the remaining coupe of deflection areas, so that I end up with no defelection but obviously dips in the board from what would be level.

 

[sparkymarky78]

Self level over that (using moisture tolerant slc) to level it out, then ditra then tile I guess.
I wanted electric ufh for the tiles so was thinking electric ufh cables on top the ditra, but guess that could be a bad thing and make humidity worse as whilst warm air holds more water than cold air and so rh would decrease, but obviously warm air also expands and so may make things worse pushing the moisture upwards - but I could very well be wrong. I could only find a post or two on the internet whether ufh makes moisture better or worse, nothing conclusive.

 

[Tile Marble Granite]

I have done similar jobs in the past, brought in a dehumidifier, had it running for 2 weeks to get rid of the humidity, then installed Hardie-Backer on top, then tiled

 

[sparkymarky78]

Was that because you had a freshly laid screed or slab though which just needed to dry out ?
I think in this case if I did that it would only be a temporary fix - this slab was laid in the 1970s so it would have dried out a long time ago. As the moisture vapour in the floor is the same in every room (high) It seems to be an ongoing thing. Outside, perimeter drains may help I suppose but I think it's due lack of or failed dpc from the 1970 (dpc weren't regs until mid 1970's so it may or may not have one.
So dehumidifier would work initially but moisture would just build up again afterwards as it comes up through slab from the ground. Thanks for the suggestion though.

I put a piece of vapour barrier on top of the backer boards the other day sealed to the floor and puy the floor moisture meter on top of that - it read 80 percent without the polythene it and 70 percent with it. So that seems it would help, or the liquid dpm but I know you said that's bad practice on top of the backer boards.
I'm going round in circles haha.

 

[Tile Marble Granite]

The similar jobs I have done were flooded at some point and needed a dehumidifier, walls and floors. To attach the Hardie-Becker to the concrete Pros would use SBR, tile adhesive Rawl plugs and screws. The best bond is done on dry surface.

You know how to get on with the project now. Send us pictures during/after