Moisture barrier for shower [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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01-11-2017, 12:10 AM
I've been pouring over threads and learning a lot but I'm in the middle of a project and haven't run across what I need.

I have work to do on 3 bathrooms. The first is a repair job. I tiled a bathtub surround in which my contractor built a niche. I used a Schluter product--I can't remember what it's called but it's fabric--to line the surround and the niche and completed the job. The problem is that when my new contractor started work on the adjoining bathroom, we found that the niche in the first bathroom was too deep and extended beyond the wall studs (there was previously a fiberglass shower in the second bathroom).

It had to be taken off and rebuilt from the second bathroom side--which means I have to re-tile it.

What do I need to do to provide the moisture barrier for the niche?

Second question is much the same only it involves entire showers. I have two that my contractor has prepped for tile. They both have a composite shower pan (Onyx) and hardibacker on the walls. Physically and financially I am not able to replace the boards but there is no moisture barrier underneath them. Is there a product that goes over the hardibacker to get a good moisture barrier before setting the tile?

I plan to tile one bathroom with marble and one with ceramic.

Thanks so much for advise!!

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01-11-2017, 07:03 AM
It sounds like you used Schluter Kerdi in the niche. It's an orange colored fabric like material.

In that shower build, how was the niche waterproofing (Kerdi) tied in to the rest of the walls? Typically the walls would also be covered in Kerdi and all the Kerdi pieces overlap each other by 2" (to maintain a waterproof joint) then the Kerdi is tiled over. So if you rebuild the niche from the back side (Shower 2), you have no way to get this overlap with the walls in Shower 1.

On Shower 2 you could use a surface applied liquid waterproofing product like Redgard . It needs to be applied in the correct thickness to work (so buying a (paint) thickness gauge is a good idea).
How does the hardibacker in Shower 2 connect to the Shower base (does it overlap a lip on the base? There needs to be some sort of "connection or seal" between the shower pan and the wall board.

John Bridge
01-11-2017, 11:01 AM
Hi Lynn, :)

You can use the liquid applied membrane in both cases. It will bone to the Kerdi in the niche as well as to the Hardi-backer. There is a cloth mesh that can be used over the joint between the walls and the tub.

01-11-2017, 02:58 PM
Yes, it was Schluter Kerdi and I did do the overlap and everything according to directions. A liquid moisture barrier sounds great but I wasn't sure it would "connect" with the Kerdi.

In the other (2 bathrooms) projects, the hardibacker does overlap the "lip" of the shower pans but there is a gap between the board and the perpendicular shower floor. What kind of mesh would I use and how would it attach to the shower pan?

Do I need to tape all the seams of the hardibacker or would the liquid moisture barrier be enough by itself?

Thanks again!!

01-12-2017, 02:11 AM
After I finish re-doing the small niche in the first bathroom I will start on the tiling the second bathroom. The contractor has put the cement board down and I will be using Redgard as a moisture barrier.

I will be using marble and tiling the floor, shower walls--one of which is a half wall with a bench. My questions is what is the best way to edge the marble tile for a newbie DIY'er. I've done 5 tiling projects before, 2 bathrooms (shower surrounds and floor) and 2 kitchens and a laundry room (tiling from the counter top to the bottom of the cabinets and tiling the floors).

I say that only to give some idea of where my skill level may be. All the previous projects were using porcelain tile and various listellos of glass, porcelain or slate.

I love the look of polished marble so that is the next large project but the edges have me really nervous. I've used bullnose or metal edging previously but bullnose isn't and option with this tile and I really don't want to use metal edging.

Should I try and bevel the edges? Cut one edge a 22° and polish it (if so, how to polish?). Leave it as is but polish it to match the shine of the field surface?

Do I need a grinder? Recommendations?


01-12-2017, 08:53 AM
I would recommend that you do not use marble - there are a lot of posts here regarding staining problems. Get a porcelain look-like-marble tile if you want that look. Such as

You could try a Schluter Profile for your edge.

Good luck.

01-12-2017, 12:43 PM
I will not be using marble on the shower floor--the shower pan is a composite (Onyx) so I will only be tiling the surround and the rest of the bathroom floor. '

I hadn't realized there were so many problems with marble in showers so i will continue to consider. I have been looking for a porcelain tile with the same look and finish but haven't seen anything. It is a very polished finished and I like the shine and "clean" look of it.

I'm probably most concerned about trying to return the marble--the boxes got rained on in the back of my truck and are basically worthless to hold the tile. They are in the garage drying out now.

I appreciate the help.

Another question: Should I use thinset and tape all the seams of my cement board floor and surround before painting with Redgard?

01-12-2017, 12:45 PM

01-16-2017, 01:29 PM
I've got my fiberglass tape to seal all my cement board seams and I've purchased John Bridge's tile book! I have a few questions--and a quick perusal through the book isn't completely clear.

I've purchased a product by Mapei and made sure it was recommended for porcelain, for tiles that are up to 20" x 20" and for floors, walls or countertops.

So, my three questions are:

Is thin set another name for mortar?
Is premix OK?
If it says good for up to 20" x 20" is it OK for a 12" x 24" tile? (I may be using this size on the floor--not on the walls)


01-16-2017, 03:13 PM
1. No. But the terms thinset and mortar are used and misused in so many ways, it's difficult to say without context. Thinset is not a product, it's a method of setting tile. Thinset mortar is a bonding product made for adhering ceramic tile to a suitable substrate. Mortar can be any number of things.

2. Absolutely not if you're wanting a thinset mortar.

3. Yes.

It would help a great deal if you'll tell use very specifically what product you're talking about. A link to the product might be even more helpful.

My opinion; worth price charged.

01-16-2017, 03:40 PM
I'm sorry CX!--I mentioned the exact product in my draft then changed everything to be more concise with the questions and forgot to put it back in.

The product is Mapei Premium Mortar. Here is a link to the pdf. fact sheet:

It says "Premium Mortar is a premixed no-mess alternative to traditional thin-set mortars that require water and mixing."

Is this a no-go? All the product possibilities are very confusing and I thought this would be a good choice since I plan to do some of the tiling in small stages (the first thing I need to do is re-tile a small niche in an otherwise complete bathroom).

Thanks again for your expertise!

01-16-2017, 04:15 PM
The industry is kind of loose with what they call mortar - I prefer to call them a mastic as in glue. Anything that comes pre-mixed CANNOT have any cement in it...the liquid in it would cause the cement to cure, starting from the moment it became wetted. IMHO, what you really want is a cement based thinset mortar that you have to mix up with water. Yes, it takes a bit more time, and you can do it in small batches, but it is both stronger and not affected by being wetted later (many of the mastics will soften if wetted for long). The other thing is how long a mastic can take to firm up...keep in mind it has about a 1-year (or longer) shelf life in that closed, slap a nearly waterproof tile on top of it...guess what, it will take a long time for it to start to get hard. Cement-based stuff cures over time, not by drying (although, some have modifiers that also needs to dry - the cement does not need it, but it is encased in a modifier in that type of thinset).

01-16-2017, 05:03 PM
Thank you so much--that makes it so much clearer!! I'll take it back and buy a dry mix (if I can figure out which one!)

02-07-2017, 05:42 PM
I'm ready to grout the tile I put on several window sills and am preparing to tile a shower surround. In both cases I'm using polished ceramic tile so I need non-sanded grout.

I've previously used a urethane grout and loved it but I was using a porcelain matte finish tile.

I was told that adding Grout Shield (Link below) instead of water to Polyblend non-sanded grout, I'll get the same "seal" and stain resistence of grouts like "'Fusion Pro". Is this true?

Link: 8P8HAQ&gclsrc=aw.ds

Anybody used this?


02-07-2017, 06:05 PM
Lynn, While Miracle is a respected name in the business, I recommend you not add anything to your cementitious grout that is not specifically recommended by the grout manufacturer. Folks have enough problems with grout when the use it per the manufacturer's recommendations.

If you want a stain resistant grout, buy and use one of those. The Fusion Pro would be a good alternative.

02-07-2017, 06:55 PM
I had Fusion Pro in my hand--but the sales person said it was a sanded grout. The package didn't say one way or another--is it just a whole different beast? So it's OK to use on glossy ceramic tile?

A much simpler solution if that's the case!


02-07-2017, 07:00 PM
Unfortunately every tile is different and the only way to know if it will scratch or not is to do a test. Fusion is a bit different than normal sanded or unsanded grout.

02-08-2017, 01:19 AM
I think rather than risking the money on a sanded grout like Fusion pro (which may scratch the tile), I'll go ahead and use the non-sanded grout mixed according to directions.

Any recommendation for a good sealer though?