Masonry mortar use as cement mortar for shower tile

[eyeglass]

My tile guy gave me 2 methods of installing ceramic tile shower wall. (Shower pan will be hot mop). Will either one of these methods cause problems. My concerns are mole development etc from condensation. ]

[b]Please advice accordingly asap as job is awaiting.
I am in Sacramento, California. Would this comply with CBC code (not a code violation)?


My tile guy, Ed, says this:
A. 6 mil poly
B. green board aka moisture resistant wall board. (I do not have the manufacturer name) with the seams covered with mesh tape.
C. wire stapled to the wallboard
D. mortar applied over the wire to create a plumb surface for the 4" tile to be applied over.
This would be done in one day.
Red Guard could be purchased and installed in between step B & C if you specified that. It would need to set/dry overnight.

OR ...

AA. 6 mil poly
BB. cement board
CC. a bonderizer primer applied over the cement board. This would have to set/dry overnight.
DD. wire nailed onto board with roofing nails
EE. mortar applied over the wire to create a plumb surface for the 4" tile to be applied over.
Georgesunray

Posts: 3
Joined: Wed Sep 01, 2010 12:51 am
Private message

[Lazarus]

Personally, I'd Kerdi it and be done with it....however, option #1 would be NOT to add redguard if there is a poly backing. Only ONE barrier. With two, you get a mold sandwich.

Of the two options...I'd have to go with the second.

[ceramictec]

without the RedGard i would worry about the staples and wired rusting out over time.

[Houston Remodeler]

Bill,

Your man Ed has me confused.

In plan A he mentions greenboard, which, should never be used in a shower and isn't listed by the TCNA as suitable for showers. "A" also has the dreaded moisture sandwich.

Plan B is fine, but why hang cement board then put a layer of cement over that? Seems to me you already have what you are looking for in the first layer of CBU.

A is out, B is acceptable. Odd to me, but acceptable.

Is this a stand alone shower or a tub shower combo?

[Lazarus]

Damn, Paul.....it's only Tuesday and I'm confused allready!

[jadnashua]

Not a fan of hot mop, but on the west coast, it's fairly common. Doesn't last as long as a good traditional mudbed or a Kerdi shower, but okay.

The bottom edge of greenboard would be sitting in the pan, and getting wet, regardless of what you do with the surface, so it's a no-go.

If the studs are in-plane, then you can just put up a vapor barrier, the cbu, and tile directly to it. The mudded wall is a good way to fix out of plumb or square walls, but if not done well, much worse than just cbu, which is already flat. It will bend if the wall studs aren't in line, since it is screwed to it.

[Jaz]

Hi George,

As you can see we don't like either method 100% but the 2nd is best. I also answered this question at the other place you posted last night.

Not sure if you have another choice on membranes. We just don't think that much of tar, well most of us don't.

As I said before, I'd go with the Kerdi method. Sounds like you allready signed on the dotted line and the project will start soon. Do you have time to re-think this?

Jaz

[Davy]

He can do either one but if he does the first one, just put the greenboard up first, then the poly, lath, mud and tile. Leave the Redgard off. I would cut the greenboard at the top of the pan and over lap the hot mop with the poly.

[Deckert]

Probably lots of ways folks do this, but you can stop the greenboard up high (like a foot off the floor), run your poly and lathe down into the pan, and you still have the blocking of the hot mop to hold your mud out. Then the mud floor locks the bottom of the wall into place.

Not sure if thats exactly what you are sayin Davy, but thats how I've done it.

[Jaz]

I doubt the wall board people would approve of poly over their board. Moisture sandwich.

That is (vapor barriers) a very confusing and misunderstood subject. (Not that I'm any more knowledgable that anyone else here). It's requirements are vague and differ depending on location. Seems to make a big diff whether it's in cold weather or hot and humid climes.

Of course I think a surface membrane is the way to go.

Jaz

[Deckert]

Yeah, I hear ya Jaz on the surface membranes.

I build Kerdi showers almost exclusively, but here in California mud (1 or 2 coat) over a hot mop pan is just the way it normally is. Its what most tile guys are used to. Its what most inspectors want to see unless you convince em otherwise. Its what builders call for 99% of the time.

[eyeglass]

Thxs for all the replies:
One big question: Cement board they planning to use is a Hardieback 1/2". with
"a bonderizer primer applied over the cement board. This would have to set/dry overnight"

Would this set up a vapor barrier with the 6mi poly on the stud?

What other cement bd can they use that will not have the fast absoption rate of a Hardie back?

I was thinking of the same to go with second method(double letter or method B) without the bonerizer.("Bondrizer primer" can you define it)

[Edthedawg]

Bill,

You got two really odd build options there, and a lot of really sound advice to go with neither of them. The 2nd one if you have no other options.

But you DO have other options.

Whyn't just put up the 1/2" CBU (Durock, Wonderboard) or Hardie, screwed to the studs w/ no poly sheeting, tape/mud the seams, and then apply a liquid waterproofing membrane (like RedGard or HydroBan) over that? Then thinset / tile / grout.

Seems you're going WAY out of your way to complicate something that's, well, fairly simple if done right.

[eyeglass]

Ed, Jax, Davy: (Shower) If I use method A in the order you described(Davy):
greenboard, the Poly, lath mud.
Would this set up a vapor trap between the greenboard and vapor 6ml?

If I ask them to use method B without the bonderizer over cement board, would that work better, assumpting the mud will set dry with the Hardie back absorption rate? or should I subtitute with Wonderbord?
I like to get back with the Contractor by today?
Thx: George/Bill

[Shaughnn]

Bill,
You installer is confused about why he's doing things which suggests to me that he's either inexperienced or he's just not curious enough to teach himself. I suspect that this is not a licensed contractor, but instead a guy who will do your project "on the side" to his regular gig. Is that correct?
When I was working in Northern California, I installed over a lot of hot mop pans. I've seen plenty of well-built hot mop pans and I've seen others which I refused to work on top of. If you are going to use a hot mop pan, make certain that it's a company with a lot of experience and a long list of recurring clients to call for references.
I recognize what "Ed" is proposing to do, but his comprehension is lacking and I'd look elsewhere for an installer. There are many different ways to put a reliable shower together. He's proposing none of them.
Shaughnn