I have just had ceramic tiles laid in my kitchen. The base floor was floorboards not concrete but I believe my contractor did put plywood down first. I think he used a flexible adhesive but ordinary grout. There is some movement in the floor which I don't think is that bad but the grout has started to crack and is getting worse. I'm not sure what to do next - can you get flexible grout that won't crack as easily or will I still have problems because there is movement in the floor?