Kerdi Shower Pan Not Sloped Enough After Installation

[CraigR2023]

I have a 100+ year old home and am remodeling one of the bathrooms myself. I removed a tub/shower insert and am creating a custom tiled shower instead. I decided to use the Kerdi product line and read up and watched videos on the system. As the old house has settled over the years, my subfloor was sloped away from the drain. I attempted to level this prior to installing the Kerdi shower pan to maintain the proper slope of the pre-sloped pan. However, the buildup on the subfloor was not enough and once the Kerdi shower pan was installed I realized the pan was unfortunately not sloping enough to the drain. I have a 60" pan with the drain at one end and need at least another 1/4"-1/2" of height along the back of the pan to create a proper slope.

Question: Can I build up a slope on top of the installed Kerdi shower pan to meet the sloping requirements of the shower (and then use Kerdi waterproof membrane to cover and seal)? I am trying to avoid attempting to remove the shower pan and likely damaging the subfloor and likely the drain. And advice is appreciated.

[cx]

Welcome, Craig.

Just one of the reasons I don't much like the foam shower trays.

I don't even know if the single-slope Schluter foam tray has even the required 1/4" per foot slope when set on a perfectly level floor and I don't have one on hand to measure. And for a 5-foot slope to drain, I'd want a bit more than that absolute minimum slope anyway. But that's not a code requirement, just a personal preference.

Given what little we know about your subfloor structure, I'd still recommend you remove the foam tray and create your own sloped floor using mortar in the form of deck mud/floor mud/dry-pack. You can compensate for the un-level floor while placing the mortar and you can create whatever slope you want.

While I suppose you could use some sort of cementitious patching material to try to repair your existing floor, it's not gonna be as easy as it might sound. And even though there are such materials that allow thicknesses down to zero, that presumes a proper substrate and I've never heard of one that would consider foam to be such a substrate.

My opinion; worth price charged.

[jadnashua]

A thixotropic self-leveling cement MIGHT work as it only flows when physically moving it then stays where you leave it, but it's not that easy to work with and it's not cheap. Mapei is one company that makes it, and you could call them to see if it would be suitable on the tray, but a mud pan is probably your best bet and least expensive option.

[John Bridge]

Hi Craig,

I wouldn't try re-sloping the foam floor. We can help you float your own shower floor as CX says. You can then cover it with Kerdi membrane and continue with the Schluter shower system. In my opinion it's either that or buy a new foam floor.

[jadnashua]

For others reading this...when using the preformed foam tray from any manufacturer, you MUST start with the floor flat and level BEFORE you then try to install the pan. There's also very little wiggle room on the drain placement.
This is critical for proper operation. A mud pan is often cheaper, and could be faster if you have to first fix the floor before installing it. The foam pan works well if the preconditions are met, as you can button up the whole thing quickly. You still need to let it sit 24-hours prior to a flood test, though when using something like Kerdi unless you happen to use the adhesive with the Noble product...then, you can flood test in 15-minutes after finishing the fabric installation. Their adhesive is lots more expensive than thinset, though. Makes a difference if you're paying for labor, but otherwise, probably not.