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How to Build a Shower Pan (Shower Floor)

Before installing the shower pan liner, it is important to build a "pre-sloped" mortar (mud) bed so that the liner when installed, will direct all moisture toward the drain's "weep holes".

preparing to build a shower pan All work done by:
Harry Dunbar

The shower shown here has a floor area of about 3 feet by 4 feet. The 2" x 10"s were installed between the studs to act as a support (blocking) for the liner. The floor is reconstructed with 3/4" plywood over 2" x 10" joists.

first ... install tar paper or other slip sheet membrane such as sheet of poly Before you begin building a showerpan, you'll need to install a slipsheet.
Although I've used roofing felt, you can use just about anything you want ... plastic garbage bags, sheet of poly, or anything similar.
lath will help strengthen the pre-sloped mortar bed

Both the mesh and the roofing paper can now be stapled to the plywood.

The mesh will allow the Deck-Mud to have some grab to the floor ensuring a solid bond and the tar paper will act as a "slip sheet" to isolate movement from the concrete or wood surface beneath the tile installation and to stop moisture from being sucked out of the mortar before cured.

shower pan drain Next I attach the bottom flange of the clamping drain assembly.
mortar mix for the pre-slope

Bill is mixing up a bag of "Sand Mix" using a latex additive to create a mixture to build the pre-sloped slab for under the liner. Using water instead of additive for the mix is also acceptable. "Sand Mix" seems to taper to 3/8" thickness around the drain better when mixed with latex additive .... but either water or latex is acceptable.
Because the mortar around the drain will be tapered fairly thin .... (about 3/8" thick), I like to use a latex additive instead of water. This almost doubles the compression strength of the mortar bed.

building the pre-slope The idea is to create a slope from the outside perimeter of the shower pan to the drain allowing any moisture caught in the liner to flow unrestricted out through the weep holes of the drain.
building the pre-slope I've brought my mortar bed about 1-1/2" up on the outside perimeter. All the material in the bed needs to be packed together as much as possible.
building the pre-slope I carefully scrape off all the mud so the surface is flat and sloped directly to the drain without any dips or high spots.

building the pre-slope Done!

A properly built mortar bed should be able to hold your weight without serious indentation immediately after it's finished (but don't do it). The following day after it has hardened, it's still soft enough to be easily chipped or gouged with just about anything hard enough to do damage. This is a normal characteristic of a perfectly built mortar-bed.

installing shower pan liner The next day I have begun installing the showerpan liner. I carefully fold excess material out of the way and staple ONLY the the highest sections of the liner and only on the outside of the curb.
installing liner and drain for shower pan I feel for the 3 bolts in the flange and carefully cut the liner to make a hole for the drain.
installing drain for shower pan
installing drain for shower pan You'll notice I've notched the liner material beside each bolt. These are the 3 areas in the drain assembly where the "weep holes" are located. Removing the liner material creates a larger hole.
installing drain for shower pan I'm applying a sealant between the liner and the bottom flange. NEVER apply a sealant between the liner and top flange. It serves no purpose other than to block the weep holes in the drain.
installing drain for shower pan keeping weep holes clear Notice the small white area beside the front bolt. That's an un-obstructed weep hole.
The liner is completed.

building a shower curb or dam using lath and mortar

I'm preparing for a mud curb by installing lath to support my mortar.

Next .... backerboard.
building a shower pan mortar bed

The cement board has been installed leaving a gap between the bottom edge of the board and the liner. This will ensure there is no wicking of moisture up into the backer board.

The lath is molded onto the curb and ONLY stapled on the outside area. Mortar when pushed against the inside section of lath will hold it into place. The mortar will also push firmly against the bottom edge of the cement board to secure it as well.

I generally leave as much as a 1/4" space between cbu panels for taping and mudding.
building a shower pan mortar bed

For the top, or finish layer of mud which is the slab the tile will be installed upon, Deck Mud is required. Deck mud although the same dry mix (4 or 5 parts sand to 1 part Portland cement) uses NO additive in the mix. Water is all that is required for a stable and workable mortar bed. To view instructions and illustrations click on the link below.

Mixing Deck Mud.

I'm working the mud bed all along the outside perimeter paying special attention to the lath and making sure it is held securely into place.

building a shower pan mortar bed The spacers around the drain are covering the weep holes so that mortar doesn't obstruct them. The little voids created by these spacers will allow moisture to quickly escape.

It's important to try and have as much as 1-1/4" of packed deck-mud around the drain. Then of course the outside perimeter will be built thicker (and higher) to accommodate a positive slope. The spacers can be buried in this process.

There should be no less than 1/4" drop per linear foot.

From the corner of shower to the drain, a distance of 3 feet would require at least a 3/4" drop.

building a shower pan mortar bed Because this is the finished slab which will support the floor tile, I'm using a level all along the outside screed.
building a shower pan mortar bed The screed is complete.
building a mortar bed, mud bed for shower pan

After the screed is finished I pack more mud between the screed and drain.

mortar bed for shower pan

While you're spreading and packing the mud you can also shave off high spots with the edge of your trowel. Take your time and do a good job.

I usually leave the edge of the drain trap slightly above the mud-bed .... about 1/8" for the tile. I always scrape away a little more if needed using a tile as a guide before the bed completely sets. You can cheat by having the Drain Trap screwed down into the flange about 3 or more turns (depending on the thickness of your tile) and then after constructing your mortar bed you can un-screw it back up to accommodate the thickness of your tile and bond coat (thinset).

mortar bed for shower floor tile The mortar bed is finished.

Remember ... the mortar bed doesn't cure hard like regular concrete, so protect it from heavy traffic (a drop-sheet works fine) until it's covered with tile.

building a shower curb or dam using lath and mortar

Constructing the Curb.

I immediately start building my showerpan curb.

I'm using a material called "Mortar Mix" mixed similar to Sand-Mix ... but a little bit wetter for this purpose. It's called "Fat Mud"

(Mortar-Mix can be found near the Portlands, Cement Mixes and bags of Sand Mix in most building supply stores.)

building a shower curb or dam using lath and mortar An artist at work.
building a shower curb or dam using lath and mortar

You can't have a better constructed or structurally sound curb than this.

The thickness of the outside and outside wall of the curb is usually around 1/2". The top of the curb is usually around 3/4" or more thick and may require corrections to create a level surface which slopes slightly into the shower. Basically ... when building a mortar bed curb you have the freedom to create whatever is required to accommodate the existing construction and size of tile you intend to use.

building a shower curb or dam using lath and mortar

Presto ... a properly constructed shower floor and curb which will pass ANY inspection.

See how I build my Kerdi Showerpans


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