The pictures you are about to see are of a shower that we took a look at in a basement bathroom.
There is a disturbing trend of basement bathrooms being renovated to an especially low standard of quality. If it's a bathroom in your home to be renovated or installed, then that means it will be used by people in the household. Therefore, it should be done properly and with all the care and attention that would go into any other bathroom in your house.
In inspecting this basement shower, it is apparent that no waterproofing was done prior to installation of the tile. Contrary to popular belief, the tiles and grout in a shower (or tub surround) DO NOT perform any type of waterproofing function. In a properly built shower, all of the waterproofing is completed before any of the tile goes up. This waterproofing can be completed in a number of different ways. What this does is provides a barrier against moisture rotting out the framing behind the walls of the bathroom, but it also allows the shower to properly dry out in between uses.
Where a shower has not been properly waterproofed, moisture will be able to seep into the backerboard (the board behind the tile) and eventually, into the wall studs. Not only is this not good for your home and your health, but it means that as the moisture builds up and the mold grows, any cleaning efforts you take in an attempt to rectify the problem will be limited in terms of fixing the inherent problem.
The fact is that whenever you run your shower, moisture is generated. Sure, most of the water goes down the drain, but what is left on the surface of the tile needs to be able to dry off so that you don't get mold and mildew build up. This buildup will occur in short order if the shower is not properly waterproofed. In a fully waterproofed shower, moisture that has worked into the tile and grout will have nowhere to travel beyond the waterproofed wallboard itself, and will dry out naturally. This drying process is also aided by the presence of a quality bathroom exhaust fan, which every bathroom should have installed. Furthermore, the exhaust fan needs to be appropriately sized for the square footage of the bathroom. An open window simply isn't good enough to expel moisture on its own - anybody who suggests this to be the case also isn't taking into account the fact that no homeowner in their right mind would want to leave a window open during the colder months of the year whilst taking a shower!
If you are renovating a bathroom and a new tub or shower will be a part of the project, you would do well to discuss the waterproofing component with your contractor. Whether you use a modern waterproofing membrane like Schluter Kerdi, or a paintable membrane like Mapei Aquadefense is up to you, but whatever ends up being used must be installed in accordance with manufacturer's directions. If not, you won't have a warranty against problems down the road, but you'll also likely be tearing the shower out to redo it as you discover the type of mold and mildew presence that comes with an improper waterproofing job (or none at all, as the photos at the end of this blog post will indicate).
In short: Tiled showers can be visually pleasing and impressive, but the necessary prep work must be done prior to the tile being installed so that you don't get mold and moisture problems down the road.