Adhesive bulging problem

[Spud]

I think it is an under fired biscuit on the tile with a excessively thick bed of adhesive which has caused the tile to bend, the poor prep work ( mist coat) didn't help but didn't cause the tiles to bend in my opinion

 

[Bruce Watt]

I have seen this before. The first time was a wall above a bath which backed on to the airing cupboard.
The paint was not removed (young and inexperienced) Weber rapid set was used.
The paint delaminated from the wall and left nothing for the adhesive to hold on to so it curled the tile. It was very bulged.
It did not appear to start for about 3 months. It started to be noted when the glaze cracked like a crackle glaze tile and continued until full desalination.
The adhesive was up to 7mm in the centre of the wall due to uneven plaster.

Thank you Jobdone,
So the quick set adhesive shrinks as it dries. If it does not have anything to grip onto, it naturally shrinks on the none grip side creating the bulging effect. Thus, I think it must follow that the adhesive must grip onto the surface first before it shrinks. interesting! That does make some sense in explaining the situation. Thanks again to all.

 

[Tile Shop]

@Paul C. Could probably help..

Sorry Andy, just seen this so thanks for point it out. I'm amazed at how much the tile has bent without it breaking completely.

I haven't read the full thread in detail but have skimmed over it so apologies if I have simply repeated anyone.

Ok, so yes the paint was a very bad idea. But regards to the movement joints in the corner, although they should be siliconed, i don't think it would have made much difference. A tiny amount maybe, ultimately it still would have failed.

The main thing that Norcros would have been better off mentioning at the time..... As others have said about the depth of adhesive, the thicker it is the more shrinkage in rapid setting adhesives will occur. The Uniflex is a C2F and is only designed for a maximum 6mm final bed depth. Norcros say it can go to 10mm but only in small isolated areas. Based on the images it is 10mm (or more) everywhere. The only reason you would need to go that deep in one hit is if the wall was so far out of true of if there were dents that needed filling, but if that was the case, it would be best practice to correct the wall first before attempting to tile it and aim for a thinner 3mm full coverage.... unless you had an adhesive designed for much thicker beds.

Jobdone has hit the nail on the head as to why the curling happened, the adhesive gripped the paint, but the paint didn't grip the plaster. However at that increased depth bed, even with a correctly prepared surface, I would still put money on a class BIII lightweight ceramic tile cracking under the stress of the rapid adhesive shrinkage. A BIa porcelain tile may be able to withstand it far better and eventually settle but tile type alone would not be a reason for such a vast depth.

Unlikely the tile is faulty, it just has a very low biscuit density so could bend to some extent, but as I have never seen a tile bend like that in 20 years, I would be interested to find out how that happened without shattering into lots of small pieces.

 

[Bruce Watt]

Sorry Andy, just seen this so thanks for point it out. I'm amazed at how much the tile has bent without it breaking completely.

I haven't read the full thread in detail but have skimmed over it so apologies if I have simply repeated anyone.

Ok, so yes the paint was a very bad idea. But regards to the movement joints in the corner, although they should be siliconed, i don't think it would have made much difference. A tiny amount maybe, ultimately it still would have failed.

The main thing that Norcros would have been better off mentioning at the time..... As others have said about the depth of adhesive, the thicker it is the more shrinkage in rapid setting adhesives will occur. The Uniflex is a C2F and is only designed for a maximum 6mm final bed depth. Norcros say it can go to 10mm but only in small isolated areas. Based on the images it is 10mm (or more) everywhere. The only reason you would need to go that deep in one hit is if the wall was so far out of true of if there were dents that needed filling, but if that was the case, it would be best practice to correct the wall first before attempting to tile it and aim for a thinner 3mm full coverage.... unless you had an adhesive designed for much thicker beds.

Jobdone has hit the nail on the head as to why the curling happened, the adhesive gripped the paint, but the paint didn't grip the plaster. However at that increased depth bed, even with a correctly prepared surface, I would still put money on a class BIII lightweight ceramic tile cracking under the stress of the rapid adhesive shrinkage. A BIa porcelain tile may be able to withstand it far better and eventually settle but tile type alone would not be a reason for such a vast depth.

Unlikely the tile is faulty, it just has a very low biscuit density so could bend to some extent, but as I have never seen a tile bend like that in 20 years, I would be interested to find out how that happened without shattering into lots of small pieces.

The finish adhesive thickness is circa 7 to 8 mm. I understand the tiler is known for thick adhesive bedding.

The tile has bent far beyond that of normal. The adhesive is holding everything in place and when the tile cracks generally the adhesive does not until it gets to a point it can not, so the adhesive is bonding all the cracked tiles together. The whole wall of tiles is shattered and the adhesive is holding everything together.
Before the tile cracks, it is amazing to see the extent of how much bend/bulge the tile can withstand with the reinforcement of the adhesive stick to the back of the tile.

 

[Tile Shop]

Can you post some pics of the cracking/shattering?

 

[Bruce Watt]

Hello Paul,
The cracks are very fine and do not photo very well for you to be able to see.
However, I feel with all you helpful tilers out there, you may like to try this for your selves. Select a large-ish tile and apply 7mm plus of quick set adhesive to the tile back, do not apply to the wall. Put to one side somewhere and over the following weeks and month watch and see what happens. If the theory is correct you should be able to reproduce the effect.
I believe for weeks and even months later the effect does grow even when you think the adhesive is dry and set.