soliciting kerdi membrane + flofx leak repair ideas

[bronzefury]

Hi,

I'm currently in the throes of waterproofing my shower pan composed of ABS Flofx Universal Bond Flange Drain Kit, Mud pan using 4:1 Mapei mud bed mix, Kerdi Membrane, Schluter All-Set (white).

I've run two 24-hour water tests so far applying different levels of water.

The first test was to check that the drain plug was not leaking. So, I filled with water above the drain plug but below the kerdi-to-bond-flange seam. The result of the test was no leaks - the water level remained the same for 24 hours.

The second test was to check that there is no leak on the seam between the bond flange drain and the kerdi membrane. The kerdi membrane was bonded to the bond flange drain using Schluter All-Set (white). So, I filled the shower pan with water to a level above the seam where the kerdi membrane attaches to the bond flange. The result was a leak - the water level fell down to close to the level of the first test (just above the drain plug but below the kerdi-to-bond-flange seam.

One theory for the failure is that the kerdi membrane did not bond well to the thinset. (I've posted a photo of the bottom side of the kerdi membrane).

Now, I have to repair the leaky section and I'm posting here to ask for help and see if the community has some good ideas.

So far, what I've done is, I've cut out a section of kerdi membrane that was on the bond flange.

My original plan was to sand down the thinset on the Flofx bond flange drain, then apply a kerdi membrane patch with a two inch overlap over the cut out section of kerdi membrane.

But, maybe, redguard on the patch area plus two inch overlap might work.

Or, another idea would be to just redguard the entire bottom of the shower pan.

I've read on some websites that redguard + kerdi isn't a good idea as it could create a mold sandwich. And its mixing two different waterproofing methods.

I"ve attached some photos.

Some of the photos contain the kerdi section I cut out, the top view of the cut out kerdi and the bottom view of the cut out kerdi. I also added photos of the second test.

20250813_182411 = underside of removed kerdi, which was bonded to thinset on flofx bond flange drain
20250813_182457 = underside of removed kerdi, which was bonded to thinset on flofx bond flange drain
20250816_181113 = topside of removed kerdi to show what I had cut out from kerdi membrane on shower pan
20250816_181251 = underside of removed kerdi to show what I had cut out from kerdi membrane on shower pan
20250810_073734 = view of second 24-hour water test to test boundary between kerdi membrane and flofx bond flange drain
20250810_074437 = closeup view of second 24-hour water test to test boundary between kerdi membrane and flofx bond flange drain

Would love to hear your ideas and thoughts. Thanks!

 

[CENTRALFL]

I would say better to ask this over on the John bridge forum. But that kerdi you pulled up looks clean, almost like it didn't bond well. How long had the all set been mixed when you applied it? Maybe it was too dry, or had started to set when you applied it and it didn't get a good adhesion to the Kerdi?

 

[Sponsor]

 

[Chucky_ott]

Ditto on the John Bridge tile forums. They are experts in everything tile.

I've done two Kerdi showers and both times were stressful. It's a learned skill. But it does look like the bond was not that great. The Schluter thinset does have a different mix ratio for thinset used to bond the membrane to the substrate. It is definitely more wet than when bonding the tile. I'd guess that your mix was too dry, you waited to long to apply the membrane, or you didn't press it in firmly enough. Also, pulling kerdi off thinset that has not set is easy enough and may not leave a lot of residue on the fleece.

 

[bronzefury]

I tried to post on johnbridge.com but for whatever reason I'm not able to post a new thread.

I stayed well within the pot life time. It was probably 20 minutes when I started putting the kerdi membrane unto the thinset working from the back of the shower to the drain.

I followed the Schluter All-Set instructions exactly using the instructions for membrane applications. I used a 1/4" x 3/16" v-notched trowel. The Schluter instructions are to use 6 - 7 quarts of water to 50lbs, so since the shower pan is 9.5 square feet so I ended up making 5 lbs thinset with 22 ounces of water. This was calculated using the following equation:

5 lbs x (7 quarts/50 lbs) = 0.7 quarts of water = 22.4 ounces of water.

I moistened the mud pan before applying thinset.

But, as you can see, the kerdi membrane still did not bond well. Before I removed the kerdi, it looked like it bonded well to the Flofx bonding flange with the thinset.

I also tried putting kerdi fix on the seam between the kerdi membrane and the bonding flange. Although the water stayed level for a while, I think 18 hours into the 24-hour test, I started noticing that the level of water was going down.

So, now I've got to figure out the best way to fix this.

 

[bronzefury]

When I try to post on johnbridge.com, I get this message

bronzefury, you do not have permission to access this page. This could be due to one of several reasons:

1. Your user account may not have sufficient privileges to access this page. Are you trying to edit someone else's post, access administrative features or some other privileged system?
2. If you are trying to post, the administrator may have disabled your account, or it may be awaiting activation.

Not sure what's changed. I think I was able to post before.