Causes of cracked limestone tiles with UFH

[jasonh15]

Hi

We have a problem with linear cracks in a newly laid limestone tiled floor.
The screed substrate at around 65-70mm thickness was laid by the builder onto the foundations, then an extra thick layer of insulation - required by building control due to extra glass in the room. The screed has wet under floor heating in it.

Then limestones tiles were laid around 4-6 weeks (he says 6 weeks but I think it more likely 4 at most) later onto flexible adhesive provided by the tile supplier.
The area is approximately 10m long and 7m wide going down to 5m.
The UFH was not ramped up and down by the builder before he laid the tiles but it was gradually eased up after the tiles were laid over a period of about a month. The work was done last summer.

The cracks started to appear as the weather got colder in the winter and the UFH was on most of the time at its max temperature. They travel in both directions and span multiple tiles, They start as hairline cracks but the limestone does flake away and the crack opens up becoming more obvious.

One interesting thing is that the cracks only appear in about 2/3 of the floor area. In about 1/3 of the floor area where a different flexible adhesive was used, because the amount supplied by the tile supplier ran out, there are no cracks whatsoever.

The builder is blaming the tile suppliers adhesive, because he says it is to be expected that the screed will crack with UFH but the flexible adhesive should take the stresses of the cracks.
However the tile supplier is saying the screed must have cracked and no flexible adhesive can prevent cracking of the tile if there is significant cracking of the screed.

The builder had attempted to take up a line of cracked tiles, to inspect for damage to the screed, but had to abandon it because of the risk of damage to the screed and UFH and the surrouding good tiles. He also though that the bit of adhesive he took up, which is said he will get analysed, seems very rigid with no feeling of elasticity too it.

Any thought on this would be much appreciated?
Would flexible adhesive that had set feel rigid or should there is a "flexible" feel to it?
It is possible to get adhseive chemically analysed to establish whether it is what is was expected to be?
With UFH should we expect screed to crack and if so should should th3e flexible adhseive handle this?
Should it be possible to perform spot repairs on the tiles/screed/adhesive without damaging the rest of the floor - is my builder just using the wrong tools?

 

[doug boardley]

was the UFH comissioned before tiling commenced?

 

[jay]

hi can we have a bit more info please as in names of adh used and what type of screed was used thanks

 

[jasonh15]

UFH was checked before the screed was laid but then not used again during the screed drying time or before the tiles were laid.

I am not sure on the exact adhesive make but I think Weber were the supplier.
Similarly on the screed but the builder said it included fibres to strengthen it in the event that cracking occurred.

 

[diamondtiling]

The UFH should have been brought up to max temperature very slowly and then brought back down again before tiling commenced, Ajax (trusted advisor) is not on right now but I know that he will tell you exactly what went wrong when he reads this thread.

:20:

 

[grumpygrouter]

It would have been beneficial to have laid a decoupling membrane like Durabase or Ditra underneath your tiles. Limestone is very fragile and the UFH and temp changes, along with the settling of the screed has transferred all the stresses through to your tiles. A decoupling membrane would have been a way to prevent this.

Flexible adhesive doesn't feel "elastic" unless it is something like BAL fastflex. Flexible means it will "move" more at molecular level when stresses are applied to it because of the polymers they are manufuctured with, not that it will bend and squash.

 

[diamondtiling]

It would have been beneficial to have laid a decoupling membrane like Durabase or Ditra underneath your tiles. Limestone is very fragile and the UFH and temp changes, along with the settling of the screed has transferred all the stresses through to your tiles. A decoupling membrane would have been a way to prevent this.

I agree with everything you have said Russ but even if he did all the above I think problems would still have arose because of not having the UFH on and allowing it to reach max temp and then cool before tiling.

 

[peckers]

you say the floor was tested prior to the screed being laid, the heating should have been turned on and run with the screed down and allowed to cool down and be turned off prior to tiling the floor. It sounds to me as if that now the heating has been used that the screed has cracked in places and it has gone threw to the tiles. It sounds like the screed has expanded once the heating has been turned on, and the spf if this is what was used couldn't keep up with the expansion rate of the screed, the heating should have not been turned on for the first two weeks once the tiling was complete and then only put on a couple of degrees and then slowly increased day by day.

You can remove the grout around the edge off the tile using a oscilating tool with a grout remover blade in it or buy a hand one if you like then you can break the tile out and inspect the screed. you shouldnt damage the heating as it is in the screed?
If the builder is blaming the adhesive company then the adhesive company can come and take away a sample and have it tested, to make sure the right adhesive was used.

The questions i would be asking is.....
1 why was the heating not turned on and commisioned with the screed down before tiling?
2 is there expansion joints in the screed around the perimeter of the room?
3 is there expansion joints for the tiles around the perimeter of the room?
4 why was there not a de-coupling membrane used, was one suggested?
5 The exact adhesive and grout used?

 

[peckers]

I agree with everything you have said Russ but even if he did all the above I think problems would still have arose because of not having the UFH on and allowing it to reach max temp and then cool before tiling.

you guys beat me to it DITTO

 

[jasonh15]

thanks for responses so far - answers to peckers questions:

1 why was the heating not turned on and commisioned with the screed down before tiling?
I'll be asking the builder/tiler but he was pushing to get the job finished quicker.
2 is there expansion joints in the screed around the perimeter of the room?
Yes there is supposed to be - I believe there is a 25mm polystyrene border
3 is there expansion joints for the tiles around the perimeter of the room?
Yes for 2 also
4 why was there not a de-coupling membrane used, was one suggested?
Not suggested. I only came across this type of thing when googling for background information.
5 The exact adhesive and grout used?
Unfortunately I do not know this - on te invoice it just says flexible. Manufacturer was Weber and Stonell were who we bought it all off.

The heating in the screed. I will suggest the method you have proposed for removing individual tiles.

 

[diamondtiling]

thanks for responses so far - answers to peckers questions:

1 why was the heating not turned on and commisioned with the screed down before tiling?
I'll be asking the builder/tiler but he was pushing to get the job finished quicker.
2 is there expansion joints in the screed around the perimeter of the room?
Yes there is supposed to be - I believe there is a 25mm polystyrene border
3 is there expansion joints for the tiles around the perimeter of the room?
Yes for 2 also
4 why was there not a de-coupling membrane used, was one suggested?
Not suggested. I only came across this type of thing when googling for background information.
5 The exact adhesive and grout used?
Unfortunately I do not know this - on te invoice it just says flexible. Manufacturer was Weber and Stonell were who we bought it all off.

The heating in the screed. I will suggest the method you have proposed for removing individual tiles.

The sentence in bold letters above may have been the start of your problems. Screed dries at 1mm per day at the correct temperature, when it was laid it should have been covered whilst it gained maximum strength, with the cold weather we have had lately drying times take longer.
I have just finished a Sandstone floor that was on a 70mm screed that also had wet UFH in the screed, the screed was allowed to dry for nearly 3 months.

Can you post some pictures?

 

[Gazzer]

10m is a long run...too long IMO for tiles without an expansion joint.
As the guys have said, the heating should have been commisioned before tiling by bringing it up to full heat over a period of days.
Again as mentioned Limestone and indeed again IMO natural stones should have a decoupling membrane added for extra safety.
And lastly the floor was not allowed time to dry before tiling even at 6 weeks !

 

[jasonh15]

Here is a picture
Consensus seems to be screed cracking is the problem here due to poor implementation of it (lack of drying time and failure to run up the UFH for a period before laying tiles). Rather than poor or non flexible adhesive.

Still difficult to explain why one third of the room remains unaffected and coincidentally that is where the different screed was used.

 

[jay]

Still difficult to explain why one third of the room remains unaffected and coincidentally that is where the different screed was used.

do you mean screed as in sub floor or screed as in tile adh

 

[Gazzer]

Still difficult to explain why one third of the room remains unaffected and coincidentally that is where the different screed was used.

There proving that not all adhesives are the same but the point being that either adhesive companies would specify the drying period as the same as we have stated.

 

[doug boardley]

the picture imo, shows that there's a stress crack in the screed

 

[jasonh15]

do you mean screed as in sub floor or screed as in tile adh

sorry I meant different adhesive not different screed - the screed was laid in one go.

Also after the tiles were laid the heating was not turned on for at least a couple of months and then only turned up in small increments over about 6 weeks.

 

[Gazzer]

do you mean screed as in sub floor or screed as in tile adh

sorry I meant different adhesive not different screed - the screed was laid in one go.

Also after the tiles were laid the heating was not turned on for at least a couple of months and then only turned up in small increments over about 6 weeks.

The heating in the screed should have been fired up to max temp BEFORE laying of tiles . It should be then lowered until its off and then wait 2 days before laying tiles.

 

[Ajax123]

Sorry Guys only just seen this one. Loks fairly straight forward. Peckers has hit most of the nails on th head in his poss as have most of the rest so my input is probably not really needed. However I will give it anyway but not till tommorrow cos I playing snooker again tonight......wish me luck:hurray:

just to start off though. Polystyrene is not a suitable edging material for screeds. It should have been a minimum 5mm compressible etherfoam type edge strip. The polystyrene is to prevet thermal briging to the structure. The screed should have been jointed into bays which reflect the underfloor heating zones and if on zone there shoudl have been expasnion releif joints at around 15m2 intervals. Also joints through any door thresholds were required. Th underflor heating MUST be comissioned prior to tiing. The effect of comissioning it acts to releive stresses within the screed. If there are stresses and the screed cracks and your tiles are on top the tiles will also crack. I would hazard a gues that if you take some tiles up th screed will almost certainly be cracked.

 

[Ajax123]

This is unlikely in my opinion to be an issue with the adhesive

 

[doug boardley]

have a good frame Al

 

[Ajax123]

have a good frame Al

I lost .....grrr!

 

[Stu Lilley]

we lay ditra or durabsae on all floors to safe guard our work...flexi adhesive is to keep your tiles bonded and not to protect against cracking....expansion joints should have been installed in the correct places when the screed was laid an mirrored when the stone was laid....i have seen these problems too many times when a builder thinks he is a tiler😳

 

[DHTiling]

we lay ditra or durabsae on all floors to safe guard our work...flexi adhesive is to keep your tiles bonded and not to protect against cracking....expansion joints should have been installed in the correct places when the screed was laid an mirrored when the stone was laid....i have seen these problems too many times when a builder thinks he is a tiler😳

OH!! How many times i have had this...:mad2:.. nothing worse than builders who know it all... jack of all trades and master of none.

 

[Stu Lilley]

yeah you would not ask a tiler to build you a house:mad2:

 

[Aston]

hi jason

the very fact the cracks go in both directions as you say, clearly shows this is expansion issue.

if it was a structural fault, the crack would be in a straight line. its a clear case of not comissioning the ufh correctly and not implementing the correct expansion measures.

it goes without saying ditra would have helped but its the other issues that have caused this to occur imo..

best of luck with this jason
ed