Tiles coming loose by the fireplace - what's the issue?

[Hamrin]

Hi!

A few months ago, I tiled around the fireplace in the basement. The space above the insert became a bit larger when I removed the built and plastered "extension," after which I used fiber cement board from Byggmax (https://www.byggmax.se/trossbottenskiva-fibercement-p07043) which I mounted onto the chimney and wall. I thought it would work well, both because it is inorganic and seems to withstand heat. Then I used regular adhesive and laid the tiles.

They have been in place for several months without any issues. I have now lit a fire, and in conjunction with this, the tiles have come loose from the adhesive, and they were more or less held only by the grout. I took them down, and none of them have any adhesive/mortar on them at all; it all remains on the fiber cement boards, see pictures.

I am now wondering if it is because the fiber cement boards move due to the heat, causing the tiles to come loose, or if it's because the adhesive can't withstand the heat? Is there another reason?

I didn't use any primer or similar on the boards before tiling, which might have been a mistake if the boards absorb moisture from the mortar—but then the tiles should have come off even before I lit the fire, one might think...

It can be added that the uppermost tiles, as seen in the picture, hold well, which might be explained by it not being as hot there.

 

[hempularen]

Did you have any primer on the board before you tiled? Admittedly, it should have released towards the board instead of the tile if that were the problem. But the purpose of a primer is to reduce the material's water absorption. If there is no primer, you can imagine that the water is absorbed into the board from the adhesive. It then doesn’t set before the water disappears.

Otherwise, a classic mistake, if the tiles come off, is that the adhesive has been left open too long so a skin forms on the adhesive before the tile is placed.

How long did it cure before you started using the stove? Heat movements, before the adhesive has fully cured, can also cause such issues. Tiles on underfloor heating should not be exposed to heat until after a month. It might be similar here.

 

[Hamrin]

Did you use any primer on the board before tiling? Admittedly, it should have come off against the board instead of the tile if that were the problem. But the purpose of a primer is to reduce the material's water absorption. If primer is missing, you can imagine that the water is drawn into the board from the adhesive. It then does not have time to set before the water disappears.

Otherwise, a classic mistake is if the tiles come loose because the adhesive has been exposed too long so a skin forms on the adhesive before the tile is applied.

How long did it cure before you started using the stove? Thermal movements, before the adhesive has fully cured, can also cause such issues. Floor tiles with underfloor heating should not be exposed to heat until after a month. It might be similar here.

No primer was used. I set the tiles directly, so minimal open time. Didn't use the stove for at least two months, so it should have cured properly.

 

[Nikorasu]

I'm betting on the fix - what did you use? For that kind of situation, you should use polymer-fix like Kiilto highflex S2 DF. It's also good to apply a thin layer of fix on the entire tile before placing it in the fix on the wall.

 

[Hamrin]

I'm guessing on the adhesive - what did you use? For such a situation, you should use polymer adhesive like Kiilto highflex S2 DF. It's also good to apply a thin layer of adhesive on the entire tile before setting it in the adhesive on the wall.

Leaning more and more towards that, especially since it's stuck on the boards and not at all on the tiles. I think I used Bauhaus Probau flexi low dust or something similar.

Thanks for the tips regarding Kiilto. Leaning towards removing the adhesive, using primer and adhesive from Kiilto.