cracking tiles

[Guvnor]

hi to All
5 months ago we had two bathrooms renovated by a builder.
the upstairs bathroom; walls were under coat plastered and a few coats of PVA were applied and then tiled all within a week. Around the room there is a two tile high border of glass tiles 100mm x 100mm each and all the other tiles are ceramic 600h x 300w. in the last month we have noticed that 3 of the glass tiles have cracked all on different walls.

the downstairs bathroom; the four walls are stud walls, lined with 12mm plywood, a few coats of PVA and then tiled within two weeks. The border is in glass mosaic and the rest of the tiles are ceramic approx 500h x 200w. three of the large tiles have hairline cracks on them.

the only thing i can think of which the two bathrooms have in common is the standard cheap and cheerful tile cement which the builder bought from Wickes.
Does anyone have an idea why this is happening?
i'm confident that there is no susidence in the building because there werent cracks in the previously decorated bathrooms or in any other wall in the house.

 

[gcol]

walls were under coat plastered and a few coats of PVA were applied...

You don't tile onto undercoat plaster and you don't use PVA in wet areas.

the four walls are stud walls, lined with 12mm plywood, a few coats of PVA and then tiled within two weeks.

I'd never fit wall tiles on ply, but if you must then you need to seal the back of the sheets and I would go for 18mm. 12mm is too thin and susceptible to warping. Much better to use plasterboard and tank it in wet areas.

the only thing i can think of which the two bathrooms have in common is the standard cheap and cheerful tile cement which the builder bought from Wickes.

It's hard to say for sure, but from what you've said, most of the prep work seems questionable.