Hot Mop Waterproofing Nightmares

When working in the hot mop shower pan business for over 20 years, your’re bound to have some stories. In some cases, you may hear about stories about bad job and in other cases stories of hot mop waterproofing nightmares. Here’s how to tell.

As with any project that is done without using the best practices or done by those with not much experience in the trade, and to be honest those just out to make a quick buck with no regard to if what they are working with is prepped correctly for them to do the best work possible. With that in mind here are some of the Hot Mop Waterproofing Nightmares that happen in the industry that have caused problems with the finished project. With a very expensive repair or even to the extent of a total tear out!

Improper or Missing Backing/Blocking

• Backing/blocking needs to be installed between all the spaces between the studs of the shower area. We have seen shower pans mopped without any backing/blocking at all
• Gaps bigger than 1” need to made solid. This can be done by additional wood framing orby using 24-gauge sheet metal.
• Bays are left open when plumbing or other obstruction prohibit the use of wood framing, again the use of 24-gauge sheet metal is the answer as it can be nailed or screwed to the face of the studs. One needs to pay attention, if the bottom plate is missing, a 90° bend of at least 2” should be made in the sheet metal and is to lay flat on the subfloor and properly nailed or screwed to the studs.
• Backing/blocking is missing outside the curb. The area outside of wet area of the shower which includes the curb needs to be solid with a minimum 2”requirement.
• Backing/blocking is not at the recommended height. Code requirements call for a minimum of 2” of waterproofing above the finished height of the curb around the entire perimeter of the shower.
• Standard practice is that a 2×10 set directly on the bottom plate of the framed wall or partitions is the optimum amount needed for your backing/blocking as it gives enough height for the shower pan liner, but also backing for any tile backer system that you plan on using by keeping the fasteners well above the transition point required. Smaller dimensional lumber can be stacked one on top of another to reach this industry standard.

Improper Slope/Curb Height

The “slope” or pitch is a requirement that needs to be paid attention too. Some shower systems work with one slope, and some require a pre-slope and a tile slope above that, basically sandwiching the waterproofing membrane between the two. The 2-slope method is used in many shower pan systems, and is the most prevalent though out the industry. That is what I will discuss here. All slope/pitch have a standard requirement, per code and best practices, ¼” minimum to ½” maximum per each foot of length from the farthest area to the drain body, all areas of shower pan must be within these requirements.

• Curb not high enough to accommodate finished floor height. This is a all to common issue that has created many a problem. Curb heights are one of the most misunderstood parts of the shower pan system. Today designers and homeowners are wanting a low profile or curb less shower appeal. Which is possible if considerations are taken into mind from the start. Rule of thumb is that if you cannot lower the wet area of the shower pan to predetermined amount that is based on the size of and the drain placement of your shower the standard curb height should be used. Which is 3-2×4”s laid flat for a height of 4-½”. This will work with most shower sizes excluding very large showers or when drain placement becomes a deterrent. Some smaller showers can work with a smaller curb height but that needs to be determined by the above criteria! Here are a few examples of what has caused issues and damage.
• One 2×4 is used as curb or not built high enough for shower size, and the pre pitch and liner system come to the top of, or close to the top of the curb. Here lays the issue, no room is left for the mud bed and tile thickness. Aka the float and set pitch. So, all that rises above the water proofing at the curb. The pitch(s) may be correct but there is no retention at that point to hold back the water that the dry pack collects as it penetrates the grout and tile on its way to the drain on its way down to the water proofing membrane as is what is supposed to happen! As the dry pack gets saturated and the water looks for the easiest route to flow, that will be at the area of least resistance which will be at the entrance to the shower where the dry pack has no waterproofing to hold it back from going outside of the wet area of the shower.
• No pitch is put below the water proofing membrane. This has been done to “make” the above scenario work. The waterproofing is applied directly to the sub floor. This may give the dry pack and tile set some retention at the curb, but the water that penetrates the tile and grout has no pitch to send it to the weep holes and will accumulate quickly and leech it way up and over the mud work on the curb and out of the wet area of your shower. Another issue is that the accumulation of water in the mud work can cause grout discoloration, tile always looking wet, and mold growth.
• Pitch is too high. If sloped to high, this usually happen at the corners, the dry pack needs to be bulit higher to give the amount or support needed for the tile as to not cause grout cracking. It can also can make the slope to the drain too steep for the costumer to accept the finished job.
• Not a smooth pitch. A sloppy prep job on the slope base prior to installing the water proofing membrane will cause areas to piddle and hold water from travelling to the weep holes. Small amounts are acceptable but any areas that hold back the area of a 50 cent piece will usually get a failed inspection and need to be fixed and re inspected.

Drain Issues

A few common issues that keep reoccurring with drains are as follows, wrong style for the application, set too high, set too low, not set level, set to close to wall.

• Drains that are not a 2-piece stack or a 3-piece adjustable clamping ring style will not work for most applications in a shower pan. The common mistake is a roof deck drain is used or a drain that is made to set in a prefabricated unit as in a fiberglass or other solid surface shower pan.
• The drain needs to be set flush with the sub floor, if not the floor needs to be raised to create that transition, it can sometimes be done by the shower pan installer but will add a charge to your pan. Caution needs to be observed if raising the sub-floor as it may affect the retention needed at the curb and the walk over distance from top of curb to shower floor height.
• Having the drain below the sub floor creates the problem of getting a good seal at the clamping ring to bottom flange of the drain. That transition needs to be as even and smooth as possible to give the membrane used a solid and full seal without any ridges, valleys, or a chance to be torn when bolting the 2-piece drain together. It can be done in certain incidences, but requires planning and the proper prep for it to work, certain details need to be met to ensure a proper install.
• A drain that is not level when set cannot be fixed by the installer. If it waterproofed as is by an installer. The tile crew will have tuff time with the finished floor not looking right due to the uneven pitch to an out of level drain. More than few showers had to tore out and re-did due to customer dissatisfaction!
• More showers are having drain placement set close to a wall. Many times, it will also be a linear drain. Clients and designers like to have the drain as close to the finished wall as possible and many contractors will set the edge of the drain body up tight to the bottom plate of the framing. This poses a problem, same as with the drain being set too low, the transition fold from the drain body flange to the wall does not give enough membrane to create a solid seal. That fold also has a chance to tear when bolting the drain together. Again there are solutions to make this work but proper planning and prep work needs to be done in advance of framing and plumbers roughing in their work.

Full Length Windows & Doors Within The Shower

This is a great look and is very popular and will only continue as people enjoy that open look of their showers! Attention to detail in the framing stage is all so important here. Just because it is on paper doesn’t mean its going to work in the field! What designers and architects desire usually can be done if the proper planning and details are understood by all parties before construction is began.

• Window or door sill set at wrong height. The need to think ahead and have the proper elevations for the rough in work are critical.
• The size of the shower plays a major role in setting the sill heights for the window or door…the bigger the shower the more depth will be needed to accommodate the pre-pitch for the water proofing membrane and the dry pack setting bed for the tile or stone…plus that material thickness itself.
• Drain placement…all slopes begin at the farthest point in the shower to the center of the drain so a large shower with a drain set to one side of the shower will increase the pitch needed to have the proper fall to the drain by as much of a factor as 2x then with a center drain.
• Drain style also plays a role, especially is the case when using a linear drain system. The longer the linear drain the more depth will be needed so the outside edges of the linear sit low enough and also not ride on the waterproofing membrane and still be low enough to set a correct dry pack bed and finish at the require elevations.
• The sill will need to be flashed with metal after the Pre-pitch is done. This is a very important step that often gets neglected and has caused major problems down the line for all those involved.

As you can see there is a lot going on with this kind of project. Many times, major repairs and/or alterations have had to be done to get a shower functional let alone to meet the original concept and desire.