Update: Several readers have noted that the membrane installation method described in this article (which is a flat membrane installation) is no longer recommended as an optimal installation method because water that penetrates through the top layer of tile or grout may rest on the membrane. Without what is known as a “pre-slope fill,” this water may never work its way to the drain. A pre-slope fill mortar bed installed under the membrane, coupled with the proper method for ensuring the mortar does not block off weep holes to the drain, can better protect the installation from standing water than may not evaporate back through the surface tile and grout. This updated method can be seen in this article at The Family Handyman. Note that the below method may still meet code in some areas, so if you are dealing with a professional installer, you may want to discuss their methodology. Next time we have a chance to follow a professional on a shower pan install, we will update this article to include the revised method.
Regular readers know that I’ve been hanging out with general contractor and carpenter Joe Bianco. In preparation for moving, Mr. and Mrs. Homeowner have tasked Joe with remodeling three full bathrooms, and he has brought in Jim and Rich from Diamond Tile to pour the shower pans and lay the tile. Jim and Rich have been laying tile for over 20 years, and I’m pleased to share how they poured the shower pans. Read on to learn how they waterproofed the shower, what materials they used, how they sloped the pan for proper drainage, and created a shower pan that’s ready for tile.
Before Jim and Rich got started, Joe and the plumber have made some important preparations. You can see a curb has been installed by stacking three 2×4’s and blocking has been added between the wall framing. Also, the subfloor has been brought up to the necessary level for the drain. The guys used concrete board because it was handy and the right thickness. However, the subfloor is usually plywood.
The plumber installed a polyurethane waterproof sheeting.
Instead of cutting the sheeting and compromising the waterproof barrier, the plumber overlapped the membrane in the corners (like hospital corners).
He used roofing nails to secure the sheeting because they have broad, flat heads. All the nails were placed at least 4″ up from the subfloor in accordance with local code.
Next, the guys installed Durock concrete board on the walls. Again, you can see the nails are at least 4″ up the wall.
After the sheeting was in place, the plumber finished with the drain flange and drain.
Here’s a look at the second bathroom after the Durock was hung and the drain completed.
Pro-Tip: Sometimes you’ll see the floor pre-sloped before the base is poured. Jim and Rich will do that when the floor is way out of level or when the drain is significantly higher than the subfloor. On these bathrooms it was not necessary.
Step 1: Clean
Before getting started, the Jim used a foxtail brush to clean away debris.
Step 2: Cover Drain
Next, Jim covered the drain with tape to prevent it from clogging.
Step 3: Mix Mud
For the shower pan, the guys used Mapei 4 to 1 Mud Bed Mix. You won’t find this at your local DIY center. Instead you’ll have to go to a local tile supplier, and each bag costs about $15.
Pro-Tip: A cheaper alternative to Mud Mix is all-purpose sand and Portland cement. Jim and Rich prefer Mud Mix because it saves time.
Pro-Tip: The average sized shower base requires 3 – 4 bags of Mud Mix.
Using a mixing paddle to mix the mud, Jim added water until he achieved the right consistency, and he targeted a “dry mix” that is just wet enough to clump together when compressed. A dry mix enables the guys to work the mud and set the necessary slope without concern that it’ll move, and it will dry just as hard.
Step 4: Pour / Spread Mud
Jim poured three buckets of mud into the shower and spread it out with a straight trowel.
Pro-Tip: Jim and Rich don’t use a wire mesh reinforcement for the shower pan because it’s not necessary, and if you’re not careful when packing and spreading the mud, you can puncture the waterproof membrane.
Step 5: Pack Edges and Corners
Since the Durock isn’t nailed at the very bottom, it can shift a slightly. To eliminate any movement, Jim packed some mud tight against the perimeter and into the corners.
Step 6: Set Mud Around Drain
Next, Jim began setting the mud around the drain, and he used a floor tile to find the appropriate height. After the tile is installed, it should be flush with the top of the drain. That means the base should allow room for the tile height plus a little extra for thinset.
Pro-Tip: The mud around the drain should be at least 1″ thick to provide a strong base.
Step 7: Set Slope
Using a 2′ level and the drain as a reference point, Jim sets the slope for the shower pan, and it should be 1/4″ to 1/2″ per foot.
After Jim determined the right slope between this corner and the drain, this corner became the new point of reference for the remaining perimeter.
Step 8: Level Perimeter
Working out of that corner, Jim leveled the rest of the perimeter, packing the mud firm. Jim also looked for gaps under the level and filled them accordingly.
Step 9: Screed and Trowel
After the drain was set and the perimeter was at the necessary slope, Jim began filling the remaining area. He used the level as a screed and the trowel to finish the mud.
Step 10: Check for Low Spots
Jim went back and carefully looked for low spots with his level. He said you can usually feel them as you work the trowel across the mud.
Pro-Tip: Jim says that failing to maintain a consistent slope and fill low areas is the most common mistake when pouring a shower pan.
Step 11: Verify Slope and Drain Height
After Jim finished filling and screeding, he went back to verify the slope of the shower base and to double-check the height around the drain.
Pro-Tip: The drain flange is threaded and the drain height can be adjusted. Just be sure to preserve the necessary slope.
Jim and Rich did two pans in this fashion, and they look great. The guys will let this set overnight before starting to lay tile.