I have just had an Armitage Shanks Idealcast bath professionally fitted. There is a shower over the bath. When I get in the bath I notice that it does move very slightly - and I thought that an Idealcast bath would be rock solid. When the old bath was taken out it was found that the edges of some floorboards needed replacing as they had rotted and disappeared (!) over the years (the old bath was a rolltop). They were also supposed to reinforce the joist nearest to the wall, but I didn't see that this had been done. Do I need to be concerned that the new bath does move slightly (the mastic has already cracked at one end, evidence of movement) or is it just one of those things? Thanks!