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Why do porcelain tiles ( 600x600 ) keep lifting after being laid. we have water underfloor heating below.

tiles laid onto OSB 18mm boards that had been primed, he used fast set flexible adhesive. Builder lifted some and re-laid them but the prob's continue....Heating was turned on only a few day's after tiling that, plus the OSB boards the reason for troubles...
If so, will I need to rip out new kitchen and replace the boards???

7 Answers from MyBuilder Tilers

Best Answer

To be honest there could be a number reasons as to why the tiles keep lifting. The first question is, was a porcelain adhesive used? Try to find the type of adhesive used and make sure it is approved for porcelain tiles, there are different types of adhesives for different types of tiles, and surfaces.
Second question, why was OSB used, WBP plywood is generally regarded as a minimum? OSB can be used to tile upon but it is quite flexible so I would always screw Hardiebacker board on top of the OSB this would reduce flexibility, reduce potential mosture rising through board and give a far superior bond between the tile and adhesive. OSB is made essentially compressed & glued wood chips. OSB is usually kept outside at timber merchants, has frost & moisture got into the timber. Allow to dry inside for 1 week if unsure!
Third question, Are you sure the heating was off for the time you stated, personnally I leave underfloor heating off for 5 - 7 days after grouting.

My advise. Do not remove the whole kitchen. remove all existing tiles from kitchen just to the plinth. If tiles go under kitchen feet, carefully raise each foot and remove tile, clean off excess adhesive from all floor area. Buy Hardiebacker250 cement boards (6mm thick). Screw the cement boards to the OSB at 200mm intervals with a 25mm screw. (screwfix turbogold 4 x 25mm are really good) re-lay tiles using BAL porcelbond flexible adhesive.
Use a 10mm minimum notched trowel to ensure a 100% surface contact between tile & adhesive.
Leave for 1 day to properly set, then grout using a flexible grout, BAL superflex or mapei ultracolour. turn heating on 3 - 5 days after grouting.

Result: 10 year floor guaranteed!


Answered 3rd Feb 2012

Loads of builders think they are tilers but are nothing like it.Anyone can lay tiles to look pretty but understanding substrates,adhesives and there limits are more important.I would expect the tilers on here to have plenty to say.One of them being,osb is not a common substrate for tiling lol.Backer board or ditra could have been put over the osb but i guess your builder is either a cheapskate or clueless.


Answered 3rd Feb 2012

You should not lay tiles on sterling board, Tiles should be laid onto marine ply or at the very least wpb exterior ply.
The adhesive needs to be specifically for porcelain

My guess is that the OSB is sucking all of the moisture out of the adhesive drying it too fast interupting the bonding process

Also is the 18mm directly onto joists? if so there will be too much movement causing the tiles to lift

The 18mm ply should be screwed to the existing floorboards and screwed every 6"


Answered 3rd Feb 2012

did you use flexible adhesive??? if not this is your problem.


Answered 3rd Feb 2012

this is easy the underfloor heating has been turned on to early the adhesive need two weeks minimum to cure before being heated otherwise it is subject to thermal shock and will just crumble.
rule of thumb leave under floor heating off for two weeks after tiling then switch on and set thermostat at one degree above floor temp if you have a decent stat with a sensor it will display the floor temp then increase by one degree every 24hrs I know this sound a drawn out process but its the only way to ensure the adhesive is not subjected to thermal shock
Just reading this again and I agree with the other comments regarding OSB This stands for Orientated strand board and not suitable for tilling directly onto. This is a combination of problems with your floor I would get you installer to put it right at his expense.


Answered 6th Feb 2012

So many problems that everyone else has already mentioned, sounds like your builder really has no idea, laying onto OSB is just such bad workmanship..............I've been laying tiles for over 15 years since I was 15 and have never had any problems with my installations. One of the guys mentioned above about understanding substrates, primers, types of differing tiling adhesives and he is so correct. Anyone can lay tiles flat and grout the real craftmanship is always in the preparation. I would advise using another builder to rectify the issue to be honest.

I have tiling throughout one of projects with underfloor heating and I left it off for over 3 weeks before gradually increasing the temperature.

Hope you manage to resolve the situation successfully.


Answered 2nd Oct 2014

Try a different adhesive for the tiles and leave heating off for a longer period of time. Have you spoken to a specialist tile fitter about this or consulted with the underfloor heating company for their suggestions?


Answered 3rd Feb 2012

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