Cracked floor tiles

[Manotea]

A couple of 50x50cm floor tiles have cracked in my 3 month old bathroom floor. They were laid onto sheets of 18mm marine ply by my builders. Leaving aside the fun of dealing with these chaps, what is the probability of success of digging out and replacing the cracked tiles without ruining the entire floor?

[neilrj]

I've had to do this, fairly straightforward and easier than you'd imagine.
Remove all grout and adhesive right down to the plywood all around the duff tiles, stitch drill a few holes in centre and then prise chunks away to get a scraper blade underneath to de-laminate the cement bond. A bolster can be used if they are a bit more stubborn but you want absolutely no grout/adhesive transmitting any hammer blows to adjacent tiles. You may be surprised how little adhesion the tiles have once the grout isn't locking them together rigidly, they may well come up virtually whole if the movement that cracked them has broken the adhesive layer down a bit. Don't be tempted to pry from adjacent good tiles - you will break edges off or discover poor bonding, and probably both!

Eye protection always, and use gloves and knee pads or you'll stain the rest of the grout red...

[rafletcher]

And of course don't touch it until the buiders have been back. Problem is, if the cracking is due to flexing in the floor then replacing the craked ones would only be a temporary measure - but you knew that anyway.

[a lower gear]

Many people wishing to tile onto a wooden floor lay the tiles on ply of various thickness and various grades but many find that some tiles crack.

The technique that I used with complete success on the advice of a builder uncle was to nail hardboard with galvanised clout nails at 4 inch centres all over (running the hardboard at right angles to the floorboards) and to use flexible waterproof grout and adhesive.

However I've always suspected the fact that we're a lightweight family may play a part in our bathroom floor not cracking.   

[Manotea]

its quite hard to ascertain what has caused the cracking. The cracks are every fine - like creases in a piece of folder paper laid flat again and go across two adjacent tiles. I'm wondering if there is a join between the ply sheets underneath. The ply was screwed to the joists below, and good quality flexible adhesive used on top.

[Viking]

I had a similar issue when I had my upstairs rebuild a few years ago.  It turned out there was a joint in the plywood right under the crack.  The builders fixed it without any hassle.

[Mr Arch]

I did a floor for a client a about 7 years ago.  One tile cracked and the client dropped something on an adjacent tile and chipped it.

I removed both tiles, with spares, as described above, removing all grout and then breaking up the tiles from the centre outwards and replaced them both.  No additional cost to the client and no further problems since.