The Natural Philosopher wrote:

On 8 Jan 2006 11:41:04 -0800, Sadly wrote:

gaffar wrote:
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

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

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.

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