Hi, Thanks for the reply. Had I known limestone was such a nightmare I never would have chosen it but the bathroom designer said it was fine as long as sealed properly. With regards to the installation/construction the only thing I can tell you us that it involved a wooden frame on a concrete (old concrete) floor, they used some sort of waterproof boards and a paint on blue rubberised/waterproofing membrane. The tiles are sealed with Lithofin. The pitch of the floor is good, ie all the water drains to the centre well. Husband thinks we should just let it dry out and then seal all the grout lines and the broken tile with silicone. The installers are confident that the waterproofing underneath is tight but surely can't be good to gave water sitting under the tiles all the time? Installers on holiday until 16th - have already emailed them with photos. I guess my questions are: 1) Is it actually doing any harm - ie could we carry on as is? 2) Would the drying out and siliconing work? Currently only the changes of plane and the axis radiating out from the drain are siliconed - the rest is normal grout (which has cracked). 3) Would it gave been better NOT to seal the tiles at all (so water could dry out through them)? 4) If the installers were to rip up the floor and replace how horrific would this be? Would all he wall tiles be wrecked too? Could the glass shower frame be removed without too much damage? I am pretty sure they said ripping up the floor would break the waterproofing. 5) Should we re-tile the floor with something other than limestone, eg marble or ceramic mosaic? I can't tell you how much I wish I had chosen another material. :-(

Reading here at GardenWeb, I know that tile and grout are not waterproof. Your guy is just not informed. Yes, we have bathrooms done "the old way" and sometimes the tile above the bathtub did stay for many years. But how many have rotten walls and floors behind them? Do yourself a favor and read up on how a shower should be built before you hire the next person, and talk about their methods and products before you hire. People are still out there, putting up materials worth thousands of dollars, not knowing what they are doing. After the leaks ruin other rooms in the house, all has to be torn out and redone. It happens all the time. Here is a current thread: http://ths.gardenweb.com/discussions/4654503/wall-underlayment-for-shower-best-practice?n=4

Proper material is silicone and its to fill a proper TCNA ANSI movement joint To give you advice id need to see photos of the tub flange detail and how the walls waterproofing is tied into the flange, id want to know how the tub is ledgered and fastened and that it is also set in a solid mud bed or supported per mfg properly. Mold begs more questions, any movement at that joint is a serious concern.

How did he construct the shower pan? Did he use cement board under the wall tiles? And what waterproofing system did he use on the walls? I suspect your problems may be due to construction mistakes rather than other sources.