Cracking in Tile Grout

[jesteh]

See if anyone can give pointers what went wrong.

Got following setup:
Anhydrite floor dried for 2 years (fully dry).
Water underfloor heating - comissioned prior to start of tiling
Area - L shape with longer dimensions 7 x 7m (does not exceed 8meters in any dimension)
BAL Prime APD used to prime screed
BAL Rapid Mat
BAL Rapidset Flexible Adhesive
Weber Joint Pro Grout
Large format porcelain tiles (600x600)

Job was done professionally with no issues and solid bed used throughout.
Underfloor heating comissioned very slowly 2 months after job completed.
At about 36deg water temperature, noticed a crack in one of the tiles and small cracks in grout throughout - cracks in grout are hardly visible but they are there. Grout otherwise seems stable.
The cracked tile is on the external corner and had to be cut to L shape so is obviously weaker.
Grout is however cracked in number of places. Shouldn't the Rapid Mat have prevented all of this?

 

[J Sid]

Flow temp seam high, I understand 28 degrees max.
Others may tell you different.
Have you spoken to BAL ?

 

[Ajax123]

36 degrees water temp is fine. That will give a surface temp about 28 and a room temp of about 22

Sounds like movement though. The floor trying to expand and contract in two different directions leads tore strains and stress within the tile face. The weakest point is the grout joint so that will crack first. A joint at that point would have helped.

 

[jesteh]

Flow temp seam high, I understand 28 degrees max.
Others may tell you different.
Have you spoken to BAL ?

Flow temperature according to manufacturer should be left around 43 degrees although it can go higher - if pump is set right, floor tempreature is then around 28 degrees. We got to around 23 degrees floor temperature before we got cracks.

Yes, I had BAL rep to have a look today. He had a quick look at the tile and said that the tile cracked due to vertical movement (only thing not covered with Rapid Mat :hurray: so obviously not their problem)

He said grout cracking is perfectly normal with underfloor heating and nothing to worry about. Then he suggested tiler should have added flexible addy to the grout to stop it cracking (which is actually incorrect).

 

[tubs]

Did the Bal Rep not mean GT1 added to the grout ?

 

[jesteh]

Obviously expansion joints would have helped. I could have split the floor into small 3m x 3m segments but that would have looked crap and was not suggested by tiler, BAL or any standard I have seen. As it is the longest length is below 7m and the whole tiled area is 30 sqm - its not a massive area!

Also, I understood the purpose of the Rapid Mat was to reduce any movement to tiles. Tiler thought its unnecessary expense to have it but I insisted to avoid exactly these sort of problems. As it is, I am left wondering if I would have had these problems had I used Ditra.

 

[jesteh]

Did the Bal Rep not mean GT1 added to the grout ?

Yes sorry, Bal rep did say tiler should have added GT1 to grout. Weber says its better not to add it as its already flexible.

 

[J Sid]

Adding to much water to the grout in mixing or washing will weaken it. I am sure the Weber rep could test for this.
Personally I use Ditra, even though I am not keen on the bal mat, which i have tried, would hope this is not the root of your problem.
All the wet underfloor heating floors I have done have used Detra with with lower flow temps and never had problems with floor or customers complaints above heat up times etc.
Was there any expansion joint round room perimeter?
Speak to Weber tec about grout cracks.

 

[White Room]

Flow temperature according to manufacturer should be left around 43 degrees although it can go higher - if pump is set right, floor tempreature is then around 28 degrees. We got to around 23 degrees floor temperature before we got cracks.

Yes, I had BAL rep to have a look today. He had a quick look at the tile and said that the tile cracked due to vertical movement (only thing not covered with Rapid Mat :hurray: so obviously not their problem)

He said grout cracking is perfectly normal with underfloor heating and nothing to worry about. Then he suggested tiler should have added flexible addy to the grout to stop it cracking (which is actually incorrect).

Surprise surprise

 

[Ajax123]

Flow temperature according to manufacturer should be left around 43 degrees although it can go higher - if pump is set right, floor tempreature is then around 28 degrees. We got to around 23 degrees floor temperature before we got cracks.

Yes, I had BAL rep to have a look today. He had a quick look at the tile and said that the tile cracked due to vertical movement (only thing not covered with Rapid Mat :hurray: so obviously not their problem)

He said grout cracking is perfectly normal with underfloor heating and nothing to worry about. Then he suggested tiler should have added flexible addy to the grout to stop it cracking (which is actually incorrect).

How did he demonstrate vertical movement. Is there a lip or a height differential either side of the crack?