Dear Tilers.

I had a kitchen floor laid by a building contractor in a rear extension which they built last year and it is one of the many things they have bodged. We kicked them offsite but that is another topic entirely.

About 3 months after the tiles were put down they started to lift and some have cracked.
They are porcelain on a mixed substrate floor. I say mixed, 3/4 of the room is a new timber suspended floor and the rest is an old concrete substrate.

The substrate floor level ran out by about 15mm from the front of the room to the back. Again really not great but given that it is a very long room this wasn't a disaster an dit was the least of my worries at the time. I asked the guys at the time to either level it somehow or not worry about it at all and leave it running out and I would work around it as it really wasn't noticeable and I wasnt planning to play snooker on it. In their wisdom they appear to have decided to attempt to not level the substrate in any way but use tons of adhesive instead to level the tiles.....

See the photo below.
That doesn't seem to me to be the right approach..... I have tiled a few rooms and I would never have done it like this. Even as an amateur it doesnt smack of being the right thing to do!

I now need to fix this and need some advice please.

1) Can I assume that the approach of laying tons of adhesive is not valid......?
2) Can I use self levelling compound across a mixed concrete/wood substrate?
3) I suspect that the suspended floor may not be as good as it could be and there may be some movement in it. How can I test the adhesive they used is flexible? How can I assess the floors movement (professionally or otherwise) to see if I can lay tiles on it or to see if the floor itself needs remedial work.
4) Finally... the best way to get the adehesive up?? Any tips?? There us UFH cabling under the adhesive which I am almost resigned to loosing anyway.

Understandably I'm not too happy about having to do this work so no antagonising posts please!

Thanks for any help.
Cheers, Scott.

photo.JPG

Hello Scott. The floor should have been levelled before tiling. It is possible to get adhesive that can be applied up to 20mm thick, do you know what adhesive was used? It's also a dot and dab fixing method, which is not a good one. Ok, solution time. I'll answer the questions in order,

1) Not a good idea to lay that much adhesive with that fixing method
2) There are levelling compounds that will go over both wood and concrete, you will need an expansion joint where the 2 substrates meet (in the SLC as well as the tiling)
3) The simplest way to check for bounce is to put a full glass of water on the floor and jump up and down! If it spills, the floor needs to be strengthened.
4) Get a mechanical breaker with a chisel attachment to get the old stuff up, get some goggles, ear defenders and a good dust mask, it's a messy job.

Hope this helps and good luck with the job.

Is that powdered adhesive or somethink else.

Hi Bri,

That is great help. All practical and to the point. One question you missed is that is there a way to see if the adhesive they put down is flexible? Is there any plasticity which is reasonbly 'obvious' if I break a chunk off. It was powdered, as I remember the bags they had in but unfortuantely I don't recall its name. The only reason I ask is that it will give me more confidence in the floor if I know they skimped and used non-flexible...

Is that glass of water to be be full to the top?? If it is there is no way its going to pass ... ;-) Good job my dads a retired joiner!

Anything I need to look out for on self levelling compound? Flexible? Can I lay straight on top of the MDF sub floor once the expansion gaps are in.. ...what covers the exapnsion gaps? Sorry to be a pain.

I would get a tiler in in at the drop of a hat but times are a bit tight at the mo. Thankfully I seem to be able to lift the 95% of the tiles undamaged!

Cheers, Scott.

I don't think there is a way of telling if the adhesive is flexible, someone may know different. Get a SLC that is flexible and suitable for use on under floor heating if you are planning on trying to save that. With the expansion gap, rather than use an unsightly pre-formed strip, use a coloured silicone to match your grout colour (mapei do matching grout/silicone) and just fill the grout line where the two subfloors meet, this keeps the look of the floor continuous. You must make sure that a grout line falls directly over the join of the wood/ concrete. I would overboard the MDF with a cement board first, then do all your levelling.

Thanks again.
One last question...I'm sure there are other posts on subfloor preperation but now I have you on a roll.....

What thickness concrete board and how to bond that to the MDF?
That's two questions but who's counting?

If you need to know anything about mountain bikes, road bikes, computers, Gilera motor bikes... give me a shout! :-)

hi scot,you can use 6mm cement tile backer boards fix them using a bed of adhesive and also screw them in as well

personally i have never yet come across a sub floor made of mdf and i would also be concerned about even using it in my mind i would also want to change this as well

mdf on contact with any water turns in to mush i would prefer a ply base to fix backerboards to

Cheers.

Not sure why I said MDF.. that would be very very bodge... It is of course 18mm(I think) ply.

scott mate, google this product ditra matting. the company who sell it is "schluter"
you need this for two type floors ie. timber/concrete.
look it up mate this will solve your problems for ever.

let us know how you get on.

Originally Posted by paul78

scott mate, google this product ditra matting. the company who sell it is "schluter"
you need this for two type floors ie. timber/concrete.
look it up mate this will solve your problems for ever.

let us know how you get on.

Not if there is deflection movement between the 2 substrates..

Cheers gents. I need to check out the deflection issue....Its going to be some time before I get to this job but I wanted to prepare myself for the worst!

looks like someone didnt back float...