How to stop floor tiles cracking?

message from Broadback on 21 May 2004

I am helping my daughter sort out her recently acquired house. The
current problem is cracked floor tiles at the entrance of the kitchen
from the lounge.

I have started to carefully remove these and found the cause. The
kitchen is a concrete floor while the lounge is suspended wood, sadly
the lounge floor extends a few inches into the kitchen.

The tiles have cracked where the wood has flexed. Now how can I stop
this from happening again when I replace the cracked tiles? Putting
cement over the wood will not work, as that is what was already done, a
thicker layer would raise the floor at that point unacceptably.

TIA
John

BigWallop replied to Broadback on 21 May 2004

It is a point of "how to prevent the timber from expanding and contracting more
than the concrete" that's the problem. The timber is going to move a lot more
than you can really prevent, and so the only solution I can think of, is to lay
the new tiles on a bed of soft silicone sealant. Remember to remove any and all
the old adhesives from the floor before putting anything else down on top of it,
or you could end up with a point that makes the tile rock and will break it even
quicker.

A thick bed of silicone will allow the tiles to move around much more than solid
adhesives, but the grout will also crack more because of this movement.

So you're stuck with straight replacement using the same technique as the
original, or going with silicone and replacing the grout rather than the whole
tiles ever so often.

N. Thornton replied to BigWallop on 22 May 2004

thats guaranteed to make the tiles all crack. I have exactly that, and
oh boy, its crazy paving tiling. Tiles need total rigidity, any
bending of the support and they crack like eggs. Basically tiles have
very little strength when bent, thus must be isolated absolutely from
any bending forces.

I'd stiffen the wood any and every way possible. Thick sheet steel
under the tiles might possibly help, but only if absolutely rigid, and
you'd need far more than 2mm for that. More in the region of 7-10mm
I'd think. Less than that is going to be pointless.

If there is enough depth for cement, you might possibly try using a
1:1.5 mix plus added fibres. This lot is going to be hugely stronger
than what might well be just 6:1 or 4:1 there now. But you still need
to get the wood as rigid as poss. Replacing 3/4" pine boards with 3/4"
ply would help some too, if they run the right way to make that
practical. In fact better would be to use even thicker boards, and
shave them down where they cross the joists. Thick ply is not cheap,
but it may well be worth it to make this job work.

Tiles can be glued back together using epoxy adhesive: try to get some
the same colour as the tiles though :)

In short its not easy to make this work, you'll need to employ every
means possible and cross your fingers.

Regards, NT

Ian Stirling replied to N. Thornton on 23 May 2004

<snip>

What about removing the wood boards up to the threshold, then either
replacing with much thicker, or nice thick cement?

Grunff replied to Broadback on 21 May 2004

Screw down a sheet of 3/4" wbp, prime with pva, then tile. Live with the
height difference.

stuart noble replied to Grunff on 21 May 2004

Or replace the floorboards with the ply if you have access to the joists
either side. Or reinforce the boards with a couple of screws at every joist.
Rather than the wood flexing, it could just be movement as you walk on them.

Pete C replied to Broadback on 21 May 2004

Hi,

A sheet of 2 or 3mm steel under each tile would stop it cracking and
not raise the floor level by much. A flexible grout would also stop
cracks appearing between the tiles.

cheers,
Pete.

jacob replied to Broadback on 21 May 2004

Just remove the tiles back to the solid floor and finish off with a
bit of wood trim or something. You can't really lay tiles directly on
to a suspended floor.

cheers

Jacob

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