1st time tiling over existing floor pan - questions [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-03-2014, 08:32 AM

I am a DIY'er who is remodeling my bathroom. I have done a full bathroom remodel in the past (walls and floors down to studs and built up from scratch) so I am not thoroughly without skills and knowledge.

So here is my issue - I removed the tile from the walls and shower pan. I will be putting in new cement board and waterproofing the walls with a liquid membrane (used before on the last remodel). The issue is with the shower pan. On the last project, we had a tub which I removed and put in a pre-made shower slope (KBRS brand). On this project, I removed the tiles from the cement floor pan, and need some advice. I would like to keep the pan, as it seems to be in good shape, so here are my questions:

1. If there are holes in the rubber sheet, where it was nailed to the 2x4 stack curb (which I will be replacing with a taller pre-made curb), can I patch the holes? And if so, with what? Liquid membrane waterproofer? Patch material? Patch with pieces of the existing rubber liner cut from scraps? Bicycle patch?

2. When removing the tile from the pan, it seemed to pop right off the thinset, which appears to still be on the pan. Do I need to scrape/grind this off before applying the new thinset/tiling? And if so, any suggestions of what is the best way to go about this? If not, do I need to do any surface prep to the existing layer before applying the new thinset?

Thanks in advance for the replies. I am sure there will be more to come up as the project progresses.


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02-03-2014, 08:38 AM
Welcome back, Nick. :)

While there are times when I would agree to replace the shower pan and the bottom of the walls as a short-term repair, there is not case at all where I would replace the shower walls and re-use an existing shower pan.

Traditional shower pans are just too simple and too inexpensive not to replace and start your fifty-year life cycle all over again.

But that's up to you, of course.

As for trying to patch your traditional liner, the method for that would depend upon what material it is. Do you know the difference between PVC and CPE as it applies to such material? PVC is the more commonly used material in that application, but CPE is used extensively in some parts of the country.

My opinion; worth price charged.

02-03-2014, 09:37 AM
Hi CX,

Thanks for the quick reply.

What are the reasons for not using the existing pan? Just curious...

I have never done a cement pan before. I would probably purchase a shower basin from KBRS (with side walls and curb attached), as I had a great experience with using this product before.

02-03-2014, 10:04 AM
Not knowing the condition of it, Nick, and the receptor (pan) being the most critical part of the shower. Pan might have been working fine before the demolition, but you'll be spending a good bit of money and effort building a new shower over a pan that's now in unknown condition.

Well, unknown except for patching at the curb, which is the most critical area of the pan to begin with.

Show us some photos of what you have, 'specially the areas where your patching and changing will be done.

02-03-2014, 11:41 AM
Here are some photos of what I am dealing with. The rubber liner was nailed through when they attached cement board to the 2x4's to tile onto.




The plan was to take out the 2x4's and replace with KBRS Hardcurb, sandwiching the rubber liner between the existing pan and the new curb, rolling it over the top and stapling/screwing it on the outside.

As for the walls, you can see the gap spaces along the "back" of the pan where the cement board will slot in, on the inside of the liner.

What about the surface of the pan? if I were able to salvage the pan, what could/should be done to it?

02-03-2014, 11:23 PM
What we can see there is why I'd not wanna build a new shower over an old shower pan. You have no real hope of adequately patching the holes in that PVC liner with it being that dirty, which is the condition you'd expect to find. Then there is the treatment, or lack thereof, of the joints between curb and walls.

Nothing at all wrong with the wood curb unless it's already water damaged. If you just want it higher, add another 2x4 on top of what you have and be sure to slope it to the drain.

But really, I'd remove everything I see there and install an adequate pre-slope if required, a new liner that is high enough, folded properly, treated with dam corners at the ends, and covered with metal lath and fat mud for a very good installation.

Can you determine whether there is a pre-slope under your existing liner?

My opinion; worth price charged.

02-05-2014, 09:49 AM
So I will be taking out the existing pan, liner, etc. I have never built a mud pan, and am a little leery about the rubber liner.

What are my other options for a waterproof layer? Can I create a sloped mud pan and then use a waterproof membrane over it (solid sheet like kerdi, or liquid membrane material)? I used the KBRS premade slope & curb in a shower remodel I did at a condo I own, and in conjunction with their waterproof liquid material, the shower stall was sealed up tight.

I would prefer to do something like that as opposed to a pre-slope, rubber sheet and then sloped pan. It seems like too many opportunities for water to collect, leaks and weeping, etc.


Thanks, Nick

Richard Tunison
02-05-2014, 10:12 AM
If that were my shower I'd use the Laticrete Hydroban system which includes a bonding flange drain.

Because of the footprint you will not find anything pre fabricated for the slope so a mud bed will be in order.

02-05-2014, 10:31 AM
So would your suggestion be to use the Laticrete liquid material over a sloped and fully dried mud bed? I would assume that similar to the KBRS liquid membrane, I would need to use fabric at the edges and seams and then roll the liquid right onto the dried mud bed (and the cement board walls)?

Richard Tunison
02-05-2014, 10:39 AM
You are going to imbed alkaline resistant mesh in thin set on all of the seams and corners of your wall board including the curb so no additional fabric will be needed,,,,,,,,,,,,,, however I always used to use fabric at the wall/floor junction just for sleeping better.

Yes the entire shower will be covered in hydroban. A bonding flange drain must be utilized in the process.

02-13-2014, 03:31 PM
Well I have decided to go the Kerdi route to waterproof my shower and have a question, as I am using this product for the first time.

The three walls of the shower stall (think 6 sided hexagon) that are to be tiled, are all 12 feet tall. Two side panels to get 12x12 tiles and the center wall to get glass/stone/ceramic mosaic. All three to the full height of 12 feet.

I am installing a shower panel with shower head, body spray jets and hand-held, which mounts on to the wall after tiling. The shower head will be no higher than 7 feet when it is mounted.

How high would you recommend I mount the kerdi membrane up the walls? Currently in the space above the area where tile was removed (again at about the 7 to 7 1/2 foot level) is painted drywall, so above the shower head level the tile would be applied directly to he painted drywall. As there is very little moisture up there (ambient moisture in the air considered), do I need to Kerdi that high? What could/should I do instead?


02-13-2014, 03:55 PM
Install kerdi up to the height of the shower head, minimum. You can go higher if you want.

Sand the painted area a little to scuff it up and give the thinset something to bond to, than you can tile right over it.

02-13-2014, 04:08 PM
And just to confirm, if I am using the Kerdi material, I can put regular drywall up as the substrate material under the Kerdi membrane? Correct?

Richard Tunison
02-13-2014, 04:20 PM

02-13-2014, 06:16 PM
Nick, it'll help if you'll keep all your project questions on one thread so folks can see what you're working on and what's been previously asked and answered. We can give it a more generic title any time you'd like to suggest one. :)
(think 6 sided hexagon)Some of us would have a difficult time thinking any other kind, eh? :D

02-13-2014, 06:52 PM
So we have broken out the old mud pan (no pre-slope, rubber liner right on the plywood) and found the flange for the drain (sioux-chief?) held in place with four framing nails. I want to get this flange out so I can use the Schluter flange. How do I go about removing the existing flange? Can I cut the subfloor around the flange? should I cut off the top of the flange and then cut inside the flange and pry the pieces out?

This is my first time working with a plywood subfloor on an upper floor. The last bathroom remodel I did was on a concrete slab and I cut out slab and installed a trench drain. So, this is all new to me.

Thanks in advance for your input and suggestions.

02-13-2014, 07:53 PM
you can either use a inside pipe cutter to remove the drain or take up the plywood. if you take up the ply you will want to remove it above the joists. so when you put it back down its supported on the edges.

02-13-2014, 11:20 PM
How big is the drain you're going to be removing?

You're going to need a 4 5/8" hole for the Kerdi drain. If you can cut a hole that size or smaller to get the existing drain out, that would be the easiest way.

02-14-2014, 03:49 PM
So, I have watched the videos of the kerdi installation. In one the installer puts up the vertical bands first, then the corners, then the horizontal bands, then the full wall sheets and finally the floor sheet.

In another the edge and corner bands are done after the sheets are installed.

Is this Kerdi's way of saying that it doesn't matter what order these are installed in?

Should I do one before the other? :scratch:


02-14-2014, 04:08 PM
It makes no difference at all, Nick. Whichever method best suits your style is the one you should use. Some of us will use some of each and sometimes overlap the membrane and not use any band at all and all on the same shower.

My opinion; worth price charged.

02-17-2014, 09:15 AM
OK, I have plumbed the new connectors for the shower panel and have installed the new Kerdi drain flange (used an internal pipe cutter, then added a 2" coupler and a new piece of pipe to make the necessary height with the kerdi base drain pieces underneath). I have drywalled and taped/mudded the walls and cut the kerdi base to size, so I should be ready to install the kerdi base with thinset.

Here is my question. When I called the tile company that I bought the kerdi kit from, I mentioned that Schluter recommends unmodified thinset for mounting the kerdi base and for applying the kerdi materials. They recommended this material instead:


saying that this is what they use with the kerdi products for applying the waterproofing membrane and edge bands. Their rationalization was that this material dries faster than unmodified thinset, thereby making the finished product ready to use sooner. Is this the correct material or should I take it back and get something else?

Also, for setting the tile onto the kerdi (as well as the painted walls above the kerdi'd space) they sold me this material:


Is this material correct? or do I need to take this back as well?

If these are not going to work, what should I get specifically for the installation I am doing?

What material to mount the kerdi base to the subfloor and to attach the kerdi membrane? And what material to lay my tile onto the kerdi membrame as well as the painted walls and floor outside the shower stall?

Thanks for all the help so far and for any forthcoming responses.


02-17-2014, 02:27 PM
Hi Nick,
It is preferred that you use the attachment method to upload your images directly into the forum database. This helps ensure the size requirements are met (the forum will auto resize uploaded images) and ensures that the images will always be displayed in your post. (Images hotlinked from 3rd party sites can disappear over time leaving your posts without the visual context originally intended).

Note-if your image files are >2MB you will have to resize them first. Handy utility for doing that is here - http://imageresizer.codeplex.com/

When using Tapatalk - Choose the camera icon and upload an image from your phone/tablet. please don't use the "insert image from link" option.

02-17-2014, 02:50 PM
Thanks for the heads up on the attachments.

Now, I could still use an answer on the questions posed regarding the thinset.

Anyone???? Anyone????

02-17-2014, 03:08 PM
Nick, take that material back and tell them you prefer to follow the manufacturer's instructions and use the correct bonding mortar. If they carry Laticrete products they will have access to 317 or 272. Each will say it meets the requirements of ANSI A118.1 when mixed with water.

02-17-2014, 08:01 PM
Thanks for the input CX. I thought that was the case.

So which should I use to bond the kerdi shower slope and the kerdi membrane?

And which for the tile on the kerdi membrane and regular painted walls?

02-18-2014, 08:49 AM
Well, after removing the floor tile, I ended up with this:

Attachment 1

I was going to remove the top layer and replace it (as the thinset is stuck to the surface), but when we started to remove it, we found this:

Attachment 2

The top layer of ply is glued to the bottom subfloor as well as screwed.

So what now??? Can I scrape/grind off the old thinset? Use an uncoupling membrane right over it???


02-18-2014, 04:25 PM
Anyone??? Anyone????

02-18-2014, 05:07 PM
You can try scraping first, Nick, but I see some grinding in your future.

Worst case you get to cut out the entire subfloor and start over at the joist tops. Never much fun, that, but sometimes a fella runs outa choices.

My opinion; worth price charged.

02-19-2014, 04:40 PM
So I ground off all the old thinset on the floor and after some trimming for the curb, will be ready to prep the floor for tiling.

Without adding any significant height to the floor, what are my options?

The last tiling job I did was on to concrete, so I am curious about what to use over the plywood subfloor.

Thanks in advance for the forthcoming replies.

Houston Remodeler
02-19-2014, 07:56 PM

If the plywood is in good shape, your options from thinnest to thickest are:

1- GreenSkin. A peel and stick membrane, about the thickness of an old dollar bill
2- Nobleseal a membrane installed with thinset, about the thickness of a quarter when installed.
3- Ditra / Stratamat installed with thinset, an "uncoupling membrane", about 1/8" to 3/16" when installed
4- 1/4" ceement board installed over thinset and held down with approved fasteners
5- Ditra XL, installed with thinset, and "uncoupling membrane" about 3/8" when installed.
6- 1/2" ceement board installed over thinset and held down with approved fasteners
7- 1.5" and larger - a mud set floor

02-27-2014, 11:37 AM
OK, so I have the mortar ground off the subfloor - and it only cost me 5 stitches in my thumb when the grinder skipped!

I have purchased the GreenSkin membrane, but when I read the installation instructions, the only referenced installation over a concrete floor. They said to reference TCA F147-05 for specifications of installing over a plywood subfloor.

Needless to say, I don't have the TCA handbook.

Can anyone provide me with the information needed to install over plywood? As this is going outside the actual shower/wet area, do I need t overlap the material? Should it butt join?

Any input is greatly appreciated.

Richard Tunison
02-27-2014, 12:18 PM
This comes from the manufacturers own mouth,,,,,,,,,,,

Our membrane will stick to virtually any substrate.

Make sure the plywood is clean and dry.

02-27-2014, 02:03 PM
Nick, F147-05 is a very out of date method for tile installation over an uncoupling membrane over double layer plywood subflooring over 24" joist spacing. The current version would be F147-13, which I believe is essentially the same as the 2005 version of that method.

There is currently no industry standard for uncoupling membranes, so if a manufacturer tells you his product is an uncoupling membrane, your choices are to believe him or not believe him.

In your application, I would not be inclined to use any peel-and-stick product over plywood in the condition we see in your photos. Entirely up to you if you wanna do that, of course.

My opinion; worth price charged.

02-28-2014, 12:04 PM
Hey CX ( or anyone else interested in throwing their hat into the ring)

Why would you not recommend peel & stick? My main concern is not raising the bathroom floor up too high. And it seems that the Green Skin is the thinnest material.