grouting cracking

[thebarber]

i, recently laid quartz floor tiles in my kitchen with electric underfloor heating,
they have been down about 2 months now and when washing the floor i noticed cracks in the grout, having a closer look at the tiles i can see very slight movement in some of them when putting weight on, not enough to crack them but movement all the same.
could this get worse?
it seems to be only where the floor heating is that this has happened.
should i lift the offending tiles and relay them or just dig out the grout and replace that.
AND
why has this happened?
the floor heating is running at around 24% c morning,
9% midday
and 24 % night.
is this too much?
any advice would be appreciated

 

[skitzee2k]

Well it is either one of two things.
Adhesive problem or a substrate problem.

Either the adhesive was incorrect or was not used right or the substrate had too much movement in it.

What is the substrate and what adhesive was used?
The heating does affect adhesive and grout but not if correct products/substrate are used so you can forget about that being the problem.

 

[thebarber]

i used the correct (flexible) adhesive & grout , but don't know what you mean by substrate....
i started with a sound concrete floor,
fixed the 10mm insulation boards which came with the underfloor heating down with flexible tile adhesive, let it set
laid the heating mat in its own layer of adhesive, let it set
then laid the tiles on top with another layer of adhesive.
could i have mixed the adhesive wrong?
the problem only seems to be where the UFH is .

 

[Richard C]

What brand adhesive & grout did you use?

 

[thebarber]

dunno, but got it off a guy i know in the trade who supplied my kitchen and sells tiles, (usually fits both) ,
i have yet to ask him what he thinks.

 

[skitzee2k]

That is a tricky one. I really doubt it has anything to do with the heating.

You mention the tiles move...this should not happen on a concrete floor, even with the thermoboard.

I would say your adhesive has failed, but that is just an educated guess...most likely to be mixed incorrectly. or troweled down wrong.

The adhesive it self doesn't really NEED to be flexible in the true sense (S1 class) to be ok with underfloor heating, a lot of the cheaper brands that call themselves 'flexible' (C2 class) can actually be used with underfloor heating and show no problems even though they shouldn't call themselves flexible (recent court cases Mapei vs Ardex )....

...what i am ranting on about is that underfloor heating is not really that much of a challenge for adhesives compare to ...say Ply overlay, so I doubt the adhesive wasn't fit for the job.

...not an easy one to fix, however if you have a tile that is loose that needs to be looked at...give each tile a tap to see if you get a hollow sound.

If they are all still firm you can try raking out your grout and redoing with a standard grout with flexible additive. This makes it more flexible than the standard flexible grouts and should fix the problem.

Good luck and keep us updated

 

[tictic]

i, recently laid quartz floor tiles in my kitchen with electric underfloor heating,
they have been down about 2 months now and when washing the floor i noticed cracks in the grout, having a closer look at the tiles i can see very slight movement in some of them when putting weight on, not enough to crack them but movement all the same.
could this get worse?
it seems to be only where the floor heating is that this has happened.
should i lift the offending tiles and relay them or just dig out the grout and replace that.
AND
why has this happened?
the floor heating is running at around 24% c morning,
9% midday
and 24 % night.
is this too much?
any advice would be appreciated

did you follow m.i. regarding turning ufh on...(thermal shock)i.e turned on to quick and to high degrees...or you could have voids under the tiles..not got 100% coverage with your adhesive did you back butter the tiles?.

 

[thebarber]

yeah! took it easy with the ufh,
didnt butter the backs but mixed the adh smooth and put plenty down,
there is a slight hollow sound in areas, when tapping but the tiles are still firmly fixed.
am thinking of leaving them till they become a problem, dont want to crack them while lifting.
what do you think ?

 

[skitzee2k]

....ok, well did you level the floor before you put the boards down? and how did you fix the boards?

The hollow sound is not a good sign, but as I said if the tiles are staying down, the quick fix would be to replace grout.

 

[thebarber]

concrete floor, insulation boards, ufh, tiles.
floor was sound prior to laying.

 

[skitzee2k]

Yeah, i got that..when you say sound, are you saying it was flat? With no dips at all? I only say this as it is pretty rare to come across a floor ready to receive tiles without levelling it first.

How did you stick the boards down?

 

[thebarber]

flatter than a witche's teet...
same flexible adhesive as used for the tiles, gave it a good week or 2 before tiling,

 

[skitzee2k]

Well, we may have to put it down to one of lifes little mysteries.
If the floor was flat, the adhesive was good spread well, the board was flat, the UFH was installed and used as M.I., the other layer of adhesive was good and spread well and the tiles were quality...the grout cracking shouldn't have happened, there shouldn't be any movement and there should be no hollow points.

Something has gone wrong, but it doesn't look like we are going to find out what.

Best bet is to re-grout with a grout and additive.

 

[thebarber]

could i have used too much adhesive?
like i said the boards have a layer, ufh in its own then tiles...
the floor's raised in total around 1 1/2"
what grout + additive do you recommend?

 

[skitzee2k]

It is possible that the adhesive has collapsed as used too thick..depends on brand though. Some are thick bed, some...not so much. Which ever brand grout you used before should have a grout additive...Bal=GT1...Weber= Ad230...Ardex E101. Don't use the flexible grout, just get the standard and mix in the additive.