Advise need for flooring

12
Found 4th Feb
I’ve recently laid my bathroom floor with tiles and the grout is cracking.
I previously had vinyl flooring which I laid hardwood over the top for extra insulation, I used pva glue to seal the wood & flexible adhesive to lay the tiles then went on to use flexible grout. Id appreciate any help with which product to buy to help. Thanks
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12 Comments
I can’t tell you why it has done it as I’m no expert, but I had this too. I just took the grout out in the places it was cracked, put new grout back in and it’s been spot on ever since.

I used plywood as mentioned below, 1 year on had no more cracking so must have been settling in movement I guess.
Edited by: "AirbusA380" 4th Feb
There must have been more movement than the grout can tolerate for it to have cracked.

When you say hardwood I assume you mean hardboard? Although much cheaper it is a poor alternative to plywood which would have been stronger and because of the cross graining of each ply it suffers significantly less shrinkage/expansion - hence a better base to tile over.

Anyway - you now have what you have. I would suggest that you cut out the areas of damaged grout using either an appropriate blade on a "Multi Tool" or a Dremmel and then re-grout. As it has happened just once it you may be lucky and it may not happen again - but in all likelihood unfortunately it probably will!



If you do scrape it out with a dremmel, do be very careful and make sure you have a steady hand. I did it once and my hand slipped. Ended up with a gouged tile. Not a pretty sight. Mind you, the end result was a massive improvement on what was there before. The grout was black with mold.
Just a thought but did you screw the hard board to the underlying floor? If not that might be why the grout is crumbling. There might be too much movement and not enough stability.
There will be movement . Or not enough grout pushed into the tiles .
Did you screw or ring nail the plywood down to the floorboards every 6 inches 150mm ? As I usually put around 150 screws per 1200x2400 sheet . Unless i had a look I couldn’t give you a 100% correct answer.
1 floor movement
2 plywood not screwed down enough or floorboards moving too .
3 not enough grout pushed into joints so it filled the joint down to the adhesive.
4 not layed correctly on to the flexible adhesive.
Good luck
What grout and adhesive did you use? Not all grout is the same. Some is 'flexible' and specifically made for floors. More research needed perhaps?
ccnp24 m ago

What grout and adhesive did you use? Not all grout is the same. Some is …What grout and adhesive did you use? Not all grout is the same. Some is 'flexible' and specifically made for floors. More research needed perhaps?



agree, you need to make sure you can use it on wood, most aren't which leads to movement in the tile.
ccnp2 h, 13 m ago

What grout and adhesive did you use? Not all grout is the same. Some is …What grout and adhesive did you use? Not all grout is the same. Some is 'flexible' and specifically made for floors. More research needed perhaps?


Forgive me if I'm wrong but does op not say they used flexible twice?
Original Poster
Thanks for all the answers, i used screws in the hardboard, used mapei flexible adhesive & mapei flexible grout. The floor feels solid with no movement I can see/feel in the tiles. I’ll try to regrout first.
Yes (s)he does and the point I was trying (obviously poorly) to make is that manufacturers formulate for flexible adherance on different surfaces in the same way different glues are used for different surfaces with some saying apply to one side and some saying apply to both. Some pull more moisture out than others. Some react. Some need to be thinner to penetrate or used on specially prepped surfaces using either chemicals or just roughed up for a grip. And the tech specs (who reads them?) will often specific max movement criteria.

Whilst writing, its also worth saying that this problem can be seasonal. I have water based UFCH and the bathroom floor shrinks/expands significantly more in winter than in summer.

And there is one more possibility. What did you do at the edge? If there is no expansion joint (ie gap of a millimetre or 5) between floor and wall, which is covered with kickboard or mastic, then wall movement can force cracking well away from the root cause of the pressure.
spay15083 h, 28 m ago

Thanks for all the answers, i used screws in the hardboard, used mapei …Thanks for all the answers, i used screws in the hardboard, used mapei flexible adhesive & mapei flexible grout. The floor feels solid with no movement I can see/feel in the tiles. I’ll try to regrout first.



how thick was the hardboard. Should be around 15mm minimum
You can buy grout specifically for wooden floors, I think it might bond differently to concrete floors. I don’t know whether ‘flexible’ covers that.

How quickly did you grout after laying the tiles? It can take up to 48 hours and sometimes then it’s not dry.

How did you put the grout in? Sometimes if it’s not pushed down enough it’ll sink leaving your tiles standing proud.
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