Grout joints cracking

[Mattash99]

Evening

1st time poster, so here goes

I have a 2 part floor, half on the original screed which has an electric matting system(supplied and fitted by the electrician) and half on the new screed which has the water system in the screed, the floor was laid about a year ago. The new screeded area is fine, no cracks in the grout, but the original area on the electric matting the grout has cracked, this isn't the 1st time, happened about 6 months ago, which I put down to the UHF being on about 100 degrees, so removed all the grout and regrouted, told the client to leave it 28 days, start it low and increase it by 5 degrees, now they're saying they haven't turned it back on and it's just started to crack again, the tiles are 600sq porcelain which have been backed, used webber SPF, not really been built up, the tiles are still solid, it has ditra down and I used Arduit FL grout and am pulling what hair I have left, out!!! Anyone got any ideas, would be massively appreciated

cheers Matt

 

[cam_low]

It's the new area floorboards?

 

[Ajax123]

It's the new area floorboards?

No it's the original screed...?? Although my thought was flexing as well.... What is the original screed floor makeup?

 

[cam_low]

Half asleep Alan lol draining day today.

 

[White Room]

Do you have any thermal boards under the ufh on the original floor which has grout cracking...

 

[Mattash99]

Not sure of the original screed make up, but it was solid. No thermal boards, straight on the original and then latexed over.

 

[Mattash99]

Do you have any thermal boards under the ufh on the original floor which has grout cracking...

No thermal boards, UHF latexed a couple of times over, then the ditra and then the tiles

 

[cam_low]

A recipe for a good solid floor. No wonder you are scratching your head.

Is there any expansion gap between the two screeds? Should there be?

 

[Mattash99]

No expansion joint, but can't see as that's the problem, as the tiles are still solid. Is there a way to see if the UFH has been switched on, as my betting is there's too much heat emanating from the mat, but then I think the tiles would sweat and then blow, so I'm still fairly confused

 

[Ian]

Has the wet UFH been turned on? Is there any chance the expansion from that side of the floor has caused movement on the side with the electric UFH?

 

[Mattash99]

The wet side has been left on, as the floors are they're only source of heat for the kitchen/diner, i did think of that possibility, but the cracks have spread about 5 linea metres from the joint and not all over the floor, probably still 70% of the floor, but not in continuous joints

 

[cam_low]

Bri has expanded (lol) on where I was going. My money is on the new screed expanding and causing the slightest pressure... Just enough to crack the grout maybe?

 

[Stef]

The mat supplied by the spark, was it for a timber or concrete floor?
I got sent down the wrong mat for a floor before but I'm not sure what the outcome would be as I never fitted it, got it exchanged.

 

[Mattash99]

Enough pressure to crack the grout, but not enough to move the tiles, maybe, you think that would move that much over 5metres without any hairline cracks appearing the tiles?? Cheers for all your help by the way

 

[Mattash99]

I'm guessing they got the right mat, doubt they'd own up to it now, but that's one thing I'll check up on

 

[Ajax123]

Only reason for grout cracking in this type of floor makeup is movement. Something is clearly moving. What are the floor dimensions. Is there any hollowness in the tiles especially round where the grout crack are. I agree with your suspicion about the 100degrees C although I suspect that is a bit of an exaggeration. It has just got really cold so have they put the heating on at a high temperature causing rapid thermal expansion and thermal shock?? Is there expansion gap around the edges of the floor. If not it could be trying to belly upwards breaking the grout as it goes.

 

[Mattash99]

Alan, something is definitely moving, just can't figure out what is doing it. The tiles are solid around where the cracks in the grout are, there is some form of expansion round the edges as they are under the units and from memory they weren't cut in tight to the walls. It was a slight exaggeration regarding the temperature, but it was extremely hot, it is basically cracked where all the matting is and I guess it's gonna come down to the heating system, is there any way on an electric system to check if it's been used, other than the tiles being hot!!