Shower Pan Membrane Ideas
The shower pan membrane is what keeps the water in the shower instead of wandering about one's house. That goes for tile showers that are built with masonry layers and not the tile ready shower pans.
A certain amount of water will seep through grout lines and tile in some cases. That fairly small amount of water will still make a terrible mess if it gets away from the shower base. It won't if the liner works properly though. It will get caught by the liner and then routed to the lower level drain holes and then down the drain and away.
In the event of bigger leaks the liner really comes into play.
Often at the edges of the floor where it intersects the walls the grout lines are small and often crack. The slightest bit of movement by the walls or the floor will generate cracks. The same happens at the wall corners. Grout lines are often small and little movements will make cracks. Those cracks can let in surprising amounts of water.
In those cases the cracks are hard to see too. It is dark in the typical shower and then you really may not look to closely at grout lines under normal circumstances anyway. Especially for glasses wearers without glasses cracked grout is hard to detect.
When A Shower Pan Membrane Is A Must
In cases of rather large leaks the liners are really a must and it is a must too that the liner be waterproof.
As you probably know most of the shower pans put together these days use a single sheet of PVC called a membrane to stop the water in a shower base. An Oatey shower pan liner sheet is typical.
This liner sheet just gets placed in the shower and run up the walls for a distance to form what really is a pool that will catch stray water.
For smaller showers a single sheet is used and for larger showers it may be necessary to glue together more than one sheet to get the job done.
The liner is put down over a sloped layer of mortar so that any water than gets to the sheet has some gravity assist to get it going to the drain. By the way, the drain holes it points to are at a lower level than the opening you see in the finished floor but it is the same drain. It is made for this purpose.
The liner is glued to the base of the drain forming a critical seal at that point. A hole is cut in the liner to fit over the drain. At the edge of that opening is where the liner is attached to the drain base.
The sheet liner goes up the walls several inches and then is attached using tacks or staples well up on the liner to prevent leaks.
As an aside, the liner goes up the stud walls and usually backing of some sort is installed between the studs to make a solid form for the masonry.
The vinyl then runs up the studs. But the thickness of the vinyl will keep the backing yet to be applied from laying flat against the studs. To solve that you can do one of two things. You can either notch the studs back to form a recess for the liner or you can put thin strips, the thickness of the liner, above the membrane to set the backer board out to match the liner thickness. Either will work.
The other tricky part of getting the liner in place is getting over the curb. Cutting the liner is likely a must to get over the curb. That takes some glue to seal whatever cuts are made. Minimize cuts and use the adhesive to get the liner watertight.
Mistakes made even by so-called professional tile setters are several.
Often instead of putting down a sloped layer of mortar and installing the liner on top of that, a shower installer will simple put the membrane sheet on the flat sub-floor and then put one layer of mortar over that sloped to the drain. This works short-term but long-term will result in a shower base soaked with water with potential for a mold filled shower base. Note that even with the best practices, the shower base layer above the liner sheet is still soaked with water but that is less soaked mortar than if all the mortar is above the waterproof layer.
The other common error when putting in showers is to put the backer board on the walls before the membrane is put in. This is much easier since you do not have to contend with heavy concrete board above the liner. What putting the liner in after the board does is limit how far up the wall you can work the liner and it is not far enough. Taking the easy way out here makes for a liner that is really too short. That especially comes into play with a stopped shower drain.
The shower pan membrane is a simple piece of vinyl but it must be installed a certain way to get the best results. That often does not happen and instead the liner gets installed in some way that will cause trouble at some point.