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Question DetailsAsked on 3/17/2017

We have a beautiful shower but we can not use it to standing water. I do not know this but logically should the s.

Should the shower membrane be 1.5inches below drain

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2 Answers



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Answered 3 years ago by Member Services


Generally, yes - depth varies with brand of drain assembly and whether shower is mud-bed laid tile or in a prefab shower pan (which in some cases is used as the membrane/liner), but an inch to three is commonly how far it is below the top of the shower drain grate.

Here is an image of what a typical tile-floored shower is built like -

The drain fitting is sealed at the tile to force the shower water to flow into the drain instead of around the perimeter of it, and the liner/membrane is clamped into the drain assembly an inch to three below that. The membrane/liner (varies somewhat with prefab shower bases, and in older showers was a lead or copper sheet rather than heavy plastic) lies on a "mud bed" of smooth-finished concrete which is sloped to drain from all directions to the drain. The membrane lies on top of this (and runs up behind the bottom of the walls and is overlain there by the wall water barrier so any wall leakage ends up in the drain) and is fastened with a clamping ring to the drain pipe assembly. This assembly has perforations or slots in it just at but ABOVE the membrane clamp level, so leakage water (coming from around the drain, thorugh the tile, or from the walls) flowing on top of the membrane goes through the holes/slots into the drain line.

Then on top of the membrane/liner there is sometimes a textured open-weave plastic drainage mesh layer (which may be the top surface of the membrane material with some brands), sometimes separate and many times not used at all - then the mud bed for the tile placement, which is (at least for the bottom inch or two) made of open-graded "dry mix" (not actually dry but made very stiff and clumpy) concrete which has a lot of voids in it, so it acts as a subdrain material under the tile but on top of the membrane/liner. So - there are actually two places in the drain assembly where water can enter the drain pipe - from the shower floor drain, and from the membrane/liner into the drain through the weep holes midway down in the drain assembly.

So - take a flashlight or long Q-tip or piece of wood as a dipstick and check if the drain is plugged in the drain assembly - because even if water is getting down to the membrane it should still be draining off it into the drain pipe and out to the sewer unless this is a new installation and the installer forgot to cut out the membrane to the inside diameter of the pipe, or failed to put a drain layer around the weep holes or the overlying mud bed is not porous and water is backingup in the med bed and coming back out at the drain. In which case call him back to fix it under warranty.

If water is backing up in the shower, assuming the membrane was properly opened up inside the drain pipe, your problem is not the membrane but in the drain line - probably a clogged up trap. Again, if new construction, shower installer should fix it - MANY installers do not plug the drain pipe with a tight fitted rag during construction, so the drain trap gets an accumulation of pieces of tile and concrete and grout and such, which either immediately causes a backup, or shortly thereafter plugs up as the rough chips in the trap catch hair and soap scum.

If not new installation, then a drain cleaning is called for. Be very careful about using a drain cleaning liquid or crystals, because many can damage the membrane, and with some brands also can eat away at the concrete above the membrane. Generally, better to have the plumber (or you) access and clean the drain trap through another route - snaking or using a hair removal tool (at almost any box or grovery store), or in cases where the debris is heavy and will not flush out when snaked then by accessing the trap from adjacent wall (rarely possible except sometimes under hig-rise prefab shower bases - usually it is in the subfloor under plywood) or more commonly from below through underlying ceiling. If in concrete slab, then means more aggressive means - using a sewer retrieval tool with camera (basically an endoscope) to remove the pieces one by one from the trap. Sometimes a pronged mechanics retrieval tool like this will work - available at any auto parts or hardware store -

, dissolving with acid if grout (which can be hard on the pipes), removing shower base to redo it entirely, or digging up some concrete slab and getting at the trap from the side.

In larger cities, if you suspect solids in the trap as the problem, you may find a drain cleaning company with one of the new mini-routers - is basically a camera-carrying larger version of a dentist's drill like flexible shaft power tool which allows you to selectively grind away at and break up hard blockages in drain pipes. Normally used to cut through pipe from inside to replace broken pipe or flanges under toilets, but some makes will reach down into a trap and cut up debris or toys or such - or retrieve dropped jewelry. (Commonly come with drilling, grinding and retrieval tips).

One other possibility - I presumed this is shower water, not sewer backup coming into the shower, in which case a sewer line blockage would be the cause.

If it is not draining out at all (or extremely slowly) then you have a blocked or mostly blocked drain or drain line that needs to cleaned out. If it drains down but slowly, pour some measured water in the shower after it has been drained out for several hours - your drain pipe holds about 2-1/2 cup of water per lineal foot if 2", 1-1/2 cup per LF if 1-1/2" pipe, so if it only takes a quart to three say before it backs up then the blockage is in your drain pipe or trap right below the shower. If it takes say more than two gallons or more before backing up, then your blockage is further along - or is draining out fairly rapidly as you pour.

Of course, if you are getting slow drainage or backup in any other drain in the house, then the blockage is likely in the main drain pipes somewhere. If backing up or gurgling at the lowest elevation drain in the house (lowest floor or basement tub/shower or floor drain usually, sometimes basement laundry tub if lowest drain in the house) both when water is run there OR elsewhere in the house then the blockage is in the sewer line to the street so you need a full-capacity sewer cleaner to rout it out to the street or septic tank. If backing up at higher elevation or more "upflow" drains but NOT at the lowest, then the blockage is in the pipes within the house between the ones backing up and the lower elevation/downflow ones which are not backing up. Almost certainly the blockage is in the drain line leading from a single fixture if only backing up there, but in the main stack or a stack branch serving several fixtures if backing up in or draining very slowly from more than one drain.

Generally speaking, if backing up within the house lines a plumber can clear it out - as can a drain cleaning contractor who can also rout out the underground sewer lines to the street or septic tank (most plumbers, unless from a plumbing AND sewer cleaning company, do not have the equipment for the full sewer line routing out, which should also be done with a full-diameter scraping router (my preference except in deteriorated/clay pipe lines) or alternatively with a sewer jetting outfit.

Answered 3 years ago by LCD

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