cracked tiles on wooden floor - HELP

[gaffar]

Apologies, slightly long post.

Recently had a new bathroom as part of new extension, floor is green backed chipboard, which was then tiled over. A week ago I was in there and heard a loud crack, 1 tile had cracked, over the course of the next couple of days 3 others the same. Tiles were put down with flexible adhesive.

I have today pulled the cracked tiles up and the cause looks like it is because the wooden boards underneath have expanded from each other leaving gaps, which is where the cracks are.

Gaps look like they were there when the original tiles went down ( as there is adhesive in them) but may have expanded (posibly due to building settlement). Gap between 1 set of 2 boards is approx 4-5 mm and between second set approx 2-3 mm. 2-3mm deep

first question, is there anything I can fill these gaps with to provide a solid base to prevent the same problem again?

second Q, whilst I was pulling up the tiles, the set adhesive also ripped up parts of the green backing on the board exposing the chipboard, is there anything I can/need to do to make it safer ior will the ahesive deal with that.

Any help appreciated for a novice tiler

Thanks Gaffar

[Dave Plowman (News)]

You need 6mm plywood on top of chipboard as a base to tile on.

[gaffar]

too late for that now as I don't really want to pull up the whole floor now, just replace the 4 broken ones, any suggestions for this?

Thanks Gaffar

[Dave Plowman (News)]

Yup - have plenty of spares as they'll just break again.

[Sadly]

Did you do the tiling, or did you pay someone?

[The Natural Philosopher]

You nee to use a thick bed of flexible, but even that won't work if

- the underlying surface is moving or

- you let water get to it. The green chip swells alarmingly when wet.

My firststab at tiling over it had the same results - and a leaking loo I missed caused all the tiles to flake off, two cracked, and I ripped the lot up and did the following

- first of all there should not be gaps in the chipboard floor,. Its traditional to run some PVA along the tongue and groove to stop them moving. If its a cheap shoddily built contract laid floor, you have a problem. You may take a chance, bit you may decide to rip it up and lay e.g. ply instead in LARGE sheest - or even a single sheet...or do the floor properly in chip GLUED together.

- now the tiles Use substantial floor grade tiles Not 4mm thick. 6-8mm thick.!!"

- now the cement..at least 6mm of flexible cement is mandatory to absorb any slight movement. That at least is likely to mean cracking grout only, not cracking tiles. Try and arrange it so lines in the underlying floor do not lie along grout lines.

So get your sunbstrate right, and don't skimp on the tiles and cement, and make sure you have no leaks and you will have success.

None of the above is ever done by contract housebuilders. Scraps of chip, badly laid, cheap thin tiles and inadequate cement spell total disaster.

[Chris Bacon]

IME it hardly "swells" at all (green "Caberfloor"). I've had a sheet outside covering something up all winter, & it's OK.

[Mungo]

Dave, since I plan on replacing some flooring in a new ensuite, would it be sensible to install 22mm (or so) plywood or a sandwich of 18mm chipboard and 6mm ply? Mungo

[gaffar]

Thanks for the advice, is very useful and will come in handy when I do decide to replace the floor in the future (as now seems inevitable). Just can't afford to at the mo

The tiler who did the job originally looks like he only laid 2-3mm thick adhesive and not as a complete bed, more in wiggly lines 1cm apart.

I need to lay back these 4 tiles and also hope the others last me 9-12 months before redoing the floor, any suggestions for these.

The options for these I was going to use was to just either lay the new adhesive filling the gaps with adhesive again, or filling the gaps with silicon to floor level and then adhesive on top.

Any comments on either.

Thanks Gaffar

[Pete C]

Hi,

I'd screw some large mending plates (metal strips with 4 holes) across the joins between the chipboard sheets to minimise movement. A wood chisel or better still a router will make a rebate for them.

Also seal the chipboard particularly where it has ripped open with some polyester resin (from Halfords, motor factor or roofing supply company)

Then fill the chipboard where ripped, to level, with flexible tile cement, add more all over and tile on top.

cheers, Pete.

[gaffar]

Thanks Pete,excellent advise, I've taken up the tiles and now sanded down the existing dried adhesive as low to the board a I can get. Next steps will be as you suggest some plates to hold the boards together, some resin to waterproof the ripped areas and then adhesive and tile.

Cheers Gaffar

[Dave Plowman (News)]

If you're still using ordinary T&G chipboard flooring without reinforcement the replacement tiles will still crack - as they did before.

[Rick Hughes]

remember as well as a flexible adhesive (I use a 2 part product) you also need a flexible grout.

Rick

[zymurgy]

Or plywoood over standard floorboards.

Good god yes, use as thick a tile as you can get away with. Mine are about 8-9mm. My floor has started to move ever so slightly under the tile recently, as I wasn't generous enough with the flexible adhesive. The ply is fixed very securely to the subfloor though, and the tiles aren't showing any sign of breaking yet. They're also very large, which is helping spread the load.

I've used wood floor tiling adhesive. Be generous !

Check.

Cheers

Paul.

[Chris Bacon]

I've seen 40mm thick terrazo slabs laid on a floor. No problems there.