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08-24-2010, 11:08 PM
I am installing a new 3' by 5' shower in my remodeled bathroom. I investigated the grout pre-slope, liner and top level of grout technique. My installer was old school and used 2 layers of roofing paper up the walls and over the floor. All seams and overlaps were sealed with Henri's. The walls were covered with 1/2" HardiBacker that extend all the way to the floor.

He put down a nice Sand Mix pre-slope. However in doing this there is no way to install the waterproof membrane. So at this point I am trying to figure out the best way to waterproof the pre-slope grout and prepare the shower pan for 2" by 2" ceramic tile.

At the Home Center I saw some Mapai waterproofing compound that looked like it was applied over a fiberglass matt. Would this work with a layer of grout over it?

I am open to comments, critiques and suggestions.

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Houston Remodeler
08-24-2010, 11:12 PM
Welcome JD,

We have a little bit of a lingo problem to fix before we can get to recommendations.

Let me see if I understand what you have:

1- Studs covered with roofing felt
2- Topped with CBU from wood subfloor to tile max height
3- a clamping drain like in the pic below
4- a sloped concrete bed placed after the CBU went in but before the liner went down.

Correct? Got a pic of the shower pan as it stands today?

tile dummy
08-25-2010, 05:13 AM
I am a little confused as well get your get some pictures post so that we can understand your situation better and recommend the best possible fix.Thank you!

08-25-2010, 06:47 AM
If I'm unnerstandin' at all, it sounds like Mr. Old School put roofing felt down the studs and all across, flat on the floor, to the drain? Then sealed all that w/ some roof patch? Then 1/2" Hardie on the studs down to the floor? Then sand topping mix over the felt on the floor, and up a few inches on the Hardie, making a sloped bed down to the drain?

If yes to all of this, luckily it sounds vaguely salvageable, insofar as you're not too heavily invested in any terribly expensive materials...

08-25-2010, 01:36 PM
that is correct. The Henri's was not the regular 208 but another compound designed to seal the roofing felt.

08-27-2010, 10:09 PM

The photo should give you a good look at the shower walls and pan. The existing mortar bed is sloped down into the drain. As you can see with the bottom of the backer board covered by the mortar bed I cannot install a PVC type membrane.

Does it make any sense to apply a waterproofing compound with a matt and then apply the top layer of mortar? If not what would be a good way to proceed with the installation?



Levi the Tile Guy
08-27-2010, 10:26 PM
You have to take the 1/2" hardi off of the walls. Put the pan liner in, then put hardi back up and float the rest of your shower pan. I guess you could cut the hardi about half way up all the way around and just remove the bottom half, but then you would be cutting into the roofing felt so I would just take it all down. Depending on fasteners used you could prolly reuse the hardi, and just be out time and a little for some more fiberglass tape.

Levi the Tile Guy
08-27-2010, 10:28 PM
oh yeah you will need to remove hardi from curb also, and wrap your curb with pan liner also. then mud your curb instead of putting hardi back on there.

08-27-2010, 11:02 PM
Whoa, whoa, whoa. If the pan is properly sloped why not Kerdi the existing configuration? I'm not sure how you'd Kerdi the drain but I'm sure someone here has a Kerdi answer. Kerdi would handle the pan and walls but adhering is the drain is my concern. Maybe hydroban the works. I'm not a hydroban guy yet but that sounds like a possibility too.

08-27-2010, 11:41 PM
kerdi as keven said.

Levi the Tile Guy
08-27-2010, 11:47 PM
I actually think I read somewhere on here last night about a drain conversion that kerdi came out with. Maybe that would work for this application, but would the roofing felt behind the 1/2" hardibacker be any sort of problem?

08-28-2010, 10:39 AM
Yes, Kerdi drain conversion would seem to be ideal for the drain, but you still have the vapor barrier moisture sandwich issue.
This would seem to be tricky, I’ve seen very old places, built by craftsman, that employed a similar technique over raised wood subfloors over unfinished crawl spaces common in my area beach houses.. I think the theory given the products they had at the time was most of the moisture would drain correctly and the little that migrated through would work down the felt and simply out through the open floor hole left around the drain opening. The actual contiguous felt sandwich techniques was used for swimming pools all the time, It was common to paste mutiple layers together. The good ones sandwiched the base felt in an actual preslope similar to the pools. (I say sandwiched in preslope but that is technically incorrect but that’s the jist of it as they split it and embedded it for protection. (kind of 2 preslopes and a final. As a testament they weren’t being ripped out for any damage at all.

In an area like mine where even AC condensate is legally allowed to be dumped under the house, it just seems to have worked successfully for many years.

I’d want to ask a lot of questions of the guy who did it and it would depend on what was beneath and then I might consider hydroban or something that isn’t actually a Vapor Barrier to avoid the sandwich issue. Technically you need to really understand what went into that construction.

I only add this as if the situation is unique and the circumstances fit, I don't want you to destroy a potentially old school but possible well constructed viable solution that can be waterproofed to today's standards with modern materials in conjunction with what you have. But it is technically challenging. Foe instance if you can hydro and marry with a kerdi drain and then you simply have the problem that your vapor barrior is actually outside the waterproof envelope or pan, but in this case it might have a way to work.

08-28-2010, 11:09 AM
The installer placed 2 layers 15# felt over the curb, under the pan and up the walls to the height of the tiled area. He then attached the Hardi-backer over the felt and ran it all the way to the floor. He then poured the pre-slope so it covered the bottom of the Hardi Backer.

His intention was to cover the preslope and down into the drain with Bitchathane and then 1 1/2 "of 5 sack cement.

08-28-2010, 11:27 AM
JD, yeah, old school...... But It can work well. When you say under the pan are you simply referring to the preslope and felt or is there some other kind of actual waterproof pan that we missed and if so why were you saying there was no liner?
But I think you are referring to what we do see there so you have to find out what his thinking was about the moisture trapped by the vapor barrier. Think as it collects on the vertical wall barrier and drips down, where is it going? The felt encompasses a pool basically so are you gradually filling it up or is it going somewhere? Does he think it will just evaporate?

Like i said in our case they were letting any escape out the subfloor hole and that worked fine in those cases. I have seen some guys tackle it by sealing it to the drain flange etc, but he would have already done that within the preslope bed.

In essence they were doing similar techniques, just using materials available at the time. I have seen plenty of proof that done right, it will last a lifetime.

08-28-2010, 11:32 AM
Paint it with Mapei Aquadefense or Hydroban or Redgaurd.

Sandwich, schmandwich.

And don't kerdi it, lots of unnessacary work, imho.


08-28-2010, 11:41 AM
I'm kind of with Gueuze's thinking on this. What I'm saying is there are options to ripping it out. While the condensation issue might be there, there might be some very easy ways to deal with it, or he might of already done it an old school but completely workable way. Otherwise you have to think about how much of an issue it is given the work he has done.

08-28-2010, 11:47 AM

By pan I meant the generic term shower pan. The felt is attached to the plywood subfloor.

08-28-2010, 11:53 AM

If I paint it with Mapei or Hydroban would I be painting the preslope and up the walls? Would the painted preslope need any additional grout or?? I had thought about painting it with Mapei and also use their fiberglass matt and run it into the drain. I would run the matt several inches up the wall and then continue the paint the rest of the way.

08-28-2010, 11:57 AM
What's under the plywood subfllor? Istfloor ceiling? basement? raw crawlspace?

08-28-2010, 11:59 AM
crawlspace, this is a one story house

08-28-2010, 12:23 PM
JD- It would need a top coat of mud, or you could do a divot and then paint it all at once. Search "frankengueuze waterproofing", and read all 40 pages or so.

Here's the link-

08-28-2010, 12:41 PM
Raw crawlspace with no finished floor, I'm thinking he might have been employing the tactic I mentioned and you have no issue with the Moisture barrier. Quite sound from a technical point of view IMHO. Just make sure you understand his concept of how the trapped moisture was going to disapate without any direct wood contact.
Even with a utility floor it's almost zero issue. Once the shower is properly waterproofed it’s only some condensed vapor and most will simply evaporate without ever draining anywhere.

As far as waterproofing the pan , while it’s not an approved application for the bitchathane, I’ve seen exactly what’s he’s done wrapping it down into the drain pipe quite often, without issues. Some might say ahead of their times, others would say hacks. Now it might be a good option to think about the value of modern materials designed for the purpose. that's your decision. Now, In my area, I'd say 90% of the high end showers are custom fiberglass pan layups tied into the drain just like that, While the moisture barrier now drains within them, the pan concept itself is very similar.

08-29-2010, 11:23 PM
Frankengueze--you saved the day or better yet the shower project. My carpenter-sheetrock guy was supposed to frame in the shower so I could install the traditional pre-slope, liner etc. Instead he went ahead and installed the backer board floor to ceiling and then placed the pre-slope. No way to install the liner.

In response I found this site and started searching for another way to finish the shower. Several people said I should tear it out and start over. Yesterday morning per your suggestion I started reading the 40 page thread on waterproofing. A few pages in I saw the photos of your installation and quickly realized you were doing what I thought was my only option, using a liquid membrane such as Mapei HPG.

I picked up the Mapei at my favorite home center and found out I could not buy the Mapei fiberglass cloth. So I substituted 4" Snow roof tape to get the seams done. I already had a lot of the fiberglass landscape cloth so I did not chase around for anything else.

I installed the HPG and tape today and liked the result. The attached pictures show pretty much the same thing many other's have posted. It was a very good day! I see a way forward to getting my shower completed and my bathroom back together.

Thank you very much for your guidance and direction.

08-30-2010, 06:47 PM
JD- glad to help, and that it's working out for you. It looks like you still need to tape and thinset some cementboard seams at your curb and window. You should really get all that done before youstart painting and laying on fabric.

Snow roof tape- didn't know there was such a thing, but I like snow roof.....for non-tile things. :deal:

Keep us posted on the landscape fabric, remember that it should be completely cured before a second coat is applied, don't get antsy and jump the gun.

Did you watch the F-gueuze videos? LOL.