Cracks In New Concrete Floors

[Markltile]

Hello all
I'm a tiler in Ireland and I get a lot of new one off houses to tile, most of these have ready mix concrete floors, the kind that's pored before any walls are built and most of these floors have cracks in them, hairline cracks and slightly bigger, I have been using the Bal decoupling membrane and similar to combat this which is a big expense to my customers.
Does anyone here have experience with this and how else could I solve this problem?

 

[Alan.P]

Depends on a lot of variables really, how long the floor has been down, still drying out / settling, construction, tile type to be used, adhesive being used, if in doubt belt and braces, easier and safer in the long run.

 

[Qwerty]

^^What he said!^^

@Ajax123 is the screed expert, he may be of help

 

[Markltile]

Hello Alan
These floors are poured early in construction and have months to dry and settle, mostly 60x60 polished or glazed porcelain primed and stuck with Dunlop set plus.
What's everyone's thoughts on using thin decoupling mat in strips to divert any movement to tile joints?

 

[Alan.P]

Hello Alan
These floors are poured early in construction and have months to dry and settle, mostly 60x60 polished or glazed porcelain primed and stuck with Dunlop set plus.
What's everyone's thoughts on using thin decoupling mat in strips to divert any movement to tile joints?

If the slabs are dry and only hairline cracks then it should be fine to fix to, I take it there's no underfloor heating ? As for using strips across the cracks, I wouldn't, if there's going to be movement you want the whole area done imho that is.

 

[Markltile]

Sometimes there is under floor heating and I go through the heating/cooling process, the cracks are open at times, maybe 1 or 2mm. The problem I have is that if im tiling a big kitchen floor of 50 Mtrs or so and there's a 1 or 2 mm crack across one end of the room it seems mad to cover the whole floor with decoupling mat.

 

[Alan.P]

Well it's a gamble, you may get away with it, you may have gotten away with it, but especially on new /er builds I would be wary ? a kitchen of 50m2 is a sizable job to have to do twice ?

 

[Ste-G]

I would always use ditra mat where any under floor heating is involed. You just have to talk with the client explain the pros and cons tell them it's worth paying the extra money now or possibly a lot more in the future.
After advice like that it's up to them. If you don't think a verbal conversation is enough to absolve you of any potential blame put it in an email just for the record. It's amazing how people can forget what's been said when the poo hits the fan.

 

[Markltile]

Thanks lads, I know what you're saying, you can't be too careful. And I have used thin decoupling mat to divert potential crack movement and off square cut expansions to tile joints with no problems as of yet but time will tell, I have also tried epoxy stitching but I don't rate it too high. I think these builders should go back to putting down sub floors and sand/cement screeds, far less problems with them.