floor tiling conundrum, how do i resolve this one?

22 Apr 2009
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United Kingdom
Hi all,

first time to tiling forum as i normally reside in the plastering one...so be kind :D

here's the problem:

gutted bathroom last year, replaced rotten floorboards with chipboard flooring and tiled onto it with 600x300 porcelain tiles using flexible adhesive and flexible grout, sounds ok so far but now i think the adhesive has given up in a couple of places and there is movement in a couple of tiles meaning all the grout has cracked and starting to crumble, so question is how is best to rectify this?

help appreciated chaps.
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Advice from a fellow plasterer (amongst other things); take it all up & start again is probably the best solution. :LOL:

First mistake was using chipboard; it’s a product of the devil & should be banned. Given the choice I always take it up & start again with minimum 18mm WBP ply. Next best option is overboard with 12mm WBP ply but that raises the threshold too much.

What make adhesive & grout was used? The DIY shed stuff is carp & invariably gives problems.

Start by reading the tiling sticky & then read the Forum archive, it’s littered with similar tales of woe. :cry:
Hiya Richard ;)

to my rescue again!

followed advice from the guy at Topps and bought products from there too, sounded like he knew exactly what he was talking about, the grout was BAL superflex, the adhesive i can't remember, was a powdered form made from tyre rubber mixed with a liquid additive that came with it.

overboarding will take the floor too high, the bathroom is done now, fitted, working and looking great...until the floor started that is, everything is fixed through the board into the floor, an enormous job to replace board, if only the tiles had come up earlier in the process it wouldn't have been much of a problem.

Nowt wrong with BAL, I won’t use anything else; but Topps is one of the most expensive places you will find to buy it but some branches will discount if you push it. Assuming your adhesive was also BAL, it could have been any one of several, was it a cement powder adhesive? I usually use Rapidset flexible combined with Superflex wide joint, always over WBP ply & I've never had any problems.

The big problem with “crapboard” is it doesn’t provide the structural stiffness & integrity of ply sheeting &, so, can be inclined to flex, particularly if the floor joist span is large or the joists themselves are marginal size or spacing which can be more of a problem with newer houses. It will also disintegrate if it gets wet, even the green moisture resistant stuff eventually. If you really must tile directly onto crapboard, a single or two part flexible adhesive/grout would probably have been more suitable as this will accommodate more flexing but they are also bloody expensive & even they won’t survive if the floor is flexing too much.

A rigid base is oh so important when tiling suspended floors; even more so if you are of portly proportions or have kids jumping up & down on it :LOL: . 18mm ply is usually enough but in some cases a 25mm play base is required with intermediate noggins to provide additional support along the edges, screwed (not nailed) through into the joists every 200mm. It’s also very important the boards are correctly laid, depending on the floor.

Your problem is almost certainly down to too much flex in the floor but contributory factors could be poor preparation or application (no offence) which, just like plastering, will always affect the sucess of the end result. Once it’s gone, there is very little you can do by way of repairs. You could take up the offending tiles & attempt a relay but it will invariably notice & there is no guarantee it won’t happen again in 6 months time.

I fear the only permanent solution will be to take the tiles up salvaging what you can; rip the crapboard up & lay a decent WBP base; the thickness & any additional support required rather depends on individual circumstances. I will only overboard if I’m not given the option to replace &, as you say, it puts a ridiculous height difference at the threshold. It’s a lot of work but really the only way to guarantee success, done properly it should last a minimum of 10 years & may well see out 20 years or more.

Got to go do some render & base plastering prep work now. :rolleyes: think I'd rather be in the garden :LOL:
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the adhesive was indeed a flexible 2 part type so think i got the right stuff there, having read your comments mate i'm convinced it's down to there being too much movement in the floor which does indeed only leave me the 'relationship with my missus testing' option of ripping out and starting again, maybe i'll send her away for a week while i do it. ;)

think it might have to wait until after summer now though, or at least some crap weather, don't want to be in a windowless room for any length of time with weather like this.

thanks again richard!

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