When a tile install is done by trained and experienced professionals, and according to tile-setting standards set forth by TCA, or TTMAC, then a warranty should be available for the tile setting...but unfortunately, that has little to do with your bathroom mold.
Now, the technology of today offers us products that can eradicate the #1 reason for premature tile failure in for example a bathroom setting, apart from substandard jobs: molds. For about 20 yrs now, we have gotten a real good grip on "water management" within a tiled subsystem - so much so that we have the products we need to, in effect, make a system 'waterproof' - which goes a long way in to making the entire system "mold proof" - by extension.
Because we now know that water management is a "system", more than a sum of the components...it involves air management (ventilation), the plumbing, the vapour barrier, the insulation, the studs, the fasteners, the wall itself, the tiles, the thinset, the membrane - and of course - the drain. The right product(s) wrongly installed is worth zero, as is a good install of the wrong products. In fact that's the reason there are so many re-dos out there (where for example, a shower stall is taken out - right back to the studs) as opposed to patch jobs.
For example, if you live in most climate zones, have a shower or bath install and...uh...somehow 'forget' about the vapour barrier, you'll have problems. If you disregard the waterproof membrane, you'll also have problems; if you only tile over greenboard, you'll probably have problems too...any one of these situations puts the expected lifetime of such an install in at around 5 years, in our experience.
In our area, and let's take a shower install as a project, we would need permits for any plumbing and any electrical work done. Apart from that, we don't see a necessity of legislating (and therefore inspecting) 'tiling'. Or "grass cutting", "painting" or "plastering" for that matter...why? In order to pass the buck of responsibility to the court? Nope - can't pass that buck!:no:
Like everything else, it falls into the homeowners lap to educate himself as to the "state of the art", then find himself a contractor that presents the technology to meet that, in keeping with financial abilities. It is also the responsibility of contractors to make sure they have the tools in their bag to meet the customers' expectations - and to advise accordingly.:yes:
So to answer your concerns, no, a sealer is not the 'last defense', by far. Grout sealers only seal against some water infiltration and (mostly) stains. Waterproofing isn't its job...nor is it the job of cbu, like DensShield, nor the best thinset you can find. But used as part of system, and if the tiling is done according to published standards, then there is a very strong chance the lifetime of a shower install, for example, could reach into decades.
Just a long way of saying what Bob said...:laughing:
