Retiling Shower Bench - HELP
I have a shower bench that the preceding contractor topped off with what appears to be 12"X36" slab of Corian or something similar. The top warped, I assume because the cycle of wetting and drying eventually overstressed the material that is used under this type of counter top. I was preparing to fix some cracks that are in the tile voids where perpendicular surfaces meet when I noticed the obvious attempt to "seal" the bench top with clear silicone. A few tugs on the seat and it came off without much of a fight. The installers had used eight large blobs of what I can only assume was some type of silicone sealant. You can imagine the mold and wetness left behind. The strange thing is that after removing the "glue", there was thinset that had been notch-troweled. Whether the previous homeowner wanted a slab bench or the contractor ran out of tiles and winged it, either way, the bench clearly was ready to be tiled and for some reason wasn't.
The main reason for this post is that the shower (including the bench) is structurally sound, sloped properly and other than the joints (which should have been caulked with a matching sanded grout/caulk). I have scraped a small area to see what the substrate is under the thinset. It is durorock or equal. I am wondering what would be the best way to proceed. I don't want to rip out the bench because I don't know if the pan liner covers the bench or is under it. I also don't know if they built the frame using wood or cement block.
Does anyone have a recommendation? I am going to be using tile to replace the top. Can I level out the existing thinset after removing loose debris and abrading the surface and then add a new layer to bond the tiles? Do I need to use a belt/drum sander to remove as much as the existing thinset as possible down to the backerboard? I don't have much time to accomplish this (we have twins on the way in less than 6 weeks) but I don't want to put on a band-aid that will cost me even more time and effort in the long run. I know that given how the shower was originally installed, I should be concerned that the mud pan was done correctly but that is a something I have to hope was done well because otherwise it would require completely redoing the shower. One benefit, if you can call it that there is a recessed light between the same joists on the floor below, so I can periodically check for any wetness to avert any catastrophic damage.
Sorry for the long question but I have a wife 7-1/2 months due with twins, so my Honey-Do list is long and I wanted to make sure I gave enough information for a quick and reliable solution.