The bathroom in our new (new to us not new new) house has a heated floor, it’s great but the grout between the floor tiles is breaking up and coming out. I assume this is as a result of it drying too fast, or not being flexible enough to cope with expansion / contraction as a result of the floor heating?

Any recommendations / suggestions for grey grout that’ll not break up?

PS, ripping it all up and starting again is not an option.

I imagine the trickiest bit will be to remove the existing grout without damaging the tiles or underfloor heating. I think dremel do an attachment with a depth stop on it you might use but could be a long job.

what’s the sub floor made from?

I would suggest you’ve got a loose / flexible floor (is it all laid on top of floorboards?), ro, more likely, the tiles haven’t stuck properly?

Make sure the grout used is flexible and waterproof …
Had the same issues with mine and it transpired they`d used normal grout – eeejits !!

Try an epoxy grout

I thought epoxy grout was just for hygiene reasons. Is it good in heated situations too?

Make sure the grout used is flexible and waterproof …

That. We had to add some chemical to our adhesive to make it more flexible

Go to Topps Tiles and get the BAL grout. Done quite a few bathrooms and I wont use anything else. Even brought it to Austria when I did a bathroom here.

Mapei ultracolour. It’s cracking for one or more of many reasons.

To eliminate deflection in the floor as a potential issue, put your hands on the floor joints flat abs get someoneelseto bounce on the floor next to you. You should only feel vibration, not movement.

Mix it fairly thick, sloppy grout is weaker