Shower walls prep for tile

sriirvineSeptember 7, 2012

Hello, we are doing a home addition with a new master and master bath. The master bath has a shower with a bench in it. Our GC has hotmopped the shower (we are in CA) and it looks good. Now I started doing research and it looks like Bill V and others recommend some sort of cement backerboard with Hydroban onto which the tile is floated?

I talked to my GC about it and he says that what he does is to put down a lath, tar paper and mud that (I hope I'm getting his terms right). His words were "I'm old-school and that has worked well for a long time".

I did a bit of looking around and it sounds like the there are some who do the hot-mop + lath-tar-mud combo, but that's the old way. The problem is that I don't know enough about this to even question him on it. Does that seem like a suitable way to prep a shower wall? Anything in particular to be careful of with this method?

We'll be using 6"x3" shower tile if that matters.


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The "old way" is the better way.

When your house falls apart in 100 years, the shower will tumble to the ground, perfectly intact.

    Bookmark   September 7, 2012 at 6:44PM
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Wow, thanks for the super quick response! I'll ask for more details from my GC, but can someone describe how this method works? Water would penetrate grout/tile and also the mud, but the tar paper would just funnel the water to the drain?

If this way is better why do so many people do things like the kerdi method?


    Bookmark   September 7, 2012 at 6:54PM
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Your "old school" guy needs to go back to school. He forgot the pan membrane. Ask him what he'll use for the pan membrane. Also, if he's doing it old school, he should be using either tar paper or plastic sheeting behind the cement board.

    Bookmark   September 7, 2012 at 10:28PM
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Hi, Bill, he is using tar paper in the shower.

I thought the pan membrane was for the shower floor? The floor and bench seat are hot mopped, or is there some sort of additional membrane that's placed on top of the hot mop?

    Bookmark   September 8, 2012 at 1:39AM
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Okay-- my bad. I missed that part. Carry on!

    Bookmark   September 8, 2012 at 10:17AM
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Could I ask a followup? I just spoke with my contractor about the shower walls he will be installing, along with a Kohler cast iron shower base. He said he doesn't need to use a membrane in addition to the durock, as long as the durock extends over the lip of the shower receptor, and all the corners/seams of the durock are sealed up. Does that sound right, oh wise ones?

    Bookmark   September 9, 2012 at 8:29PM
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I'm not one of the experts like bill or mongo, but can answer your question. NO. Absolutely not okay. Durock is NOT waterproof. Water will get through it and into your walls. You need a membrane/water barrier either behind the durock or on top of it. Perhaps you should look for a contractor that knows how to install a tile shower.

    Bookmark   September 10, 2012 at 10:48AM
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Well yikes! He's got 30 years experience, and seems very confident that the pre-fab shower base removes the problem of water getting up behind the durock.

    Bookmark   September 10, 2012 at 11:37AM
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Grout is not waterproof. Water will seep through it to the durock, then through the durock and into your wall. It will take time, but it is a matter of WHEN, not IF the water will get through.

It always amazes me the number of "experienced professionals" that don't know enough about their chosen profession to be truly competent.

    Bookmark   September 10, 2012 at 12:30PM
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I really like this guy, and hate to contradict him, but here's a case where I'll have to put on my "I'm neurotic and obsessive" hat and have him include a waterproof layer. Now that I've done some more research, I see that even the Durock website says to use a different product if waterproofing is essential.

    Bookmark   September 10, 2012 at 2:30PM
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grout and tile will SHED 90% of the water. But some does get thru, and for that reason, either a paint on waterproof surface membrane, or a tar paper or plastic vapor barrier behind the cement board is REQUIRED.

    Bookmark   September 11, 2012 at 8:08AM
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He's assuming water runs downhill (to the shower pan) which is does, but the durock will become ever so slightly damp, maybe more so if there's a pinhole or whatever. That dampness goes through to the studs behind, rotting them and promoting mould.

To a large extent, OLD SCHOOL isn't necessarily better - I would argue in almost all cases, building technology and techniques have improved (Ok, craftsmanship has probably gone downhill) - who would want a place built now, done like 100 years ago? Draughty, with dodgy electrics and lead plumbing? (ok, knob and tube can theoretically last forever)

    Bookmark   September 11, 2012 at 2:47PM
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Speaking of old school, I was surprised to read that tar paper is okay as a waterproof layer; I would have immediately thought plastic sheeting.

But I've gotta say (as I sit here listening to them demo my upstairs), seeing how stout the lathe and plaster walls are makes me understand how this house has stood for over 100 years without a problem. I didn't get that same sense from our previous house, built in 1957.

    Bookmark   September 11, 2012 at 4:30PM
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One more clarification that is bugging me. It sounds like our tile guy is considering doing the mud set with lath, tar paper and mud but without backboard. Does the 'old school' method require a backboard or drywall or does the combo just hold together without requiring the support of a drywall or backboard?


    Bookmark   September 14, 2012 at 1:10PM
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In my town greenboard is required for shower walls (although these days it seems to be purple). Here are a couple of in-progress pictures.

    Bookmark   September 14, 2012 at 4:19PM
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A floated mud wall does not need cement backer board.

Floated mud walls are usually built with tar paper, lathe, mud, and a strong shoulder.

    Bookmark   September 14, 2012 at 4:20PM
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Cement based products (like grout and backer board) are waterproof only in the sense that water does not damage them.

Water passes through them by wicking just fine.

It will then wick into the studs supporting the backer board, and slowly cause them to rot.

A vapor barrier is NOT adequate.

You need a waterproof layer between the backer and the studs, or under the tile (like Kerdi) to stop the water from the grout lines completely.

If you use the shower once a day for a single person with short showers it might survive a long time, especially if the stud cavity is not well sealed.

The air leakage will allow the water to evaporate and disperse.

Use the shower a couple times a day for longer times and problems show up remarkably fast.

    Bookmark   September 14, 2012 at 4:36PM
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mongoct, appreciate the help!

    Bookmark   September 14, 2012 at 5:08PM
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"A floated mud wall does not need cement backer board.

Floated mud walls are usually built with tar paper, lathe, mud, and a strong shoulder. "

Sorry for bring up an old thread, but I would like to know that since water will penetrate cement board or mud wall, then what is the advantage of doing a mud wall?

My contractor is doing the tar paper, lathe, mud combo with no backer board and it costs $300 more than using cement board.

Should I put a roll on water barrier on top of the mud wall?


    Bookmark   July 8, 2013 at 9:48PM
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John Whipple - By Any Design ltd.

There always seems to be so much confusion about shower construction in California. This stems I think from the states thirst for Hot Mop Shower pans. This system "hot mop" is time proven and in the state men who build showers like to float the walls out themselves.

What is missing in most of these builds is the poly or tar paper layer that goes over the wall studs. And laps over the hot mop (before mudding out the walls). Here in Vancouver you could sub out hot mop for a rubber liner - same practice.

A hot mop floor should be topped with no less than 1 1/4" of deck mud and ideally 2" or thicker - something like a Laitcrete 3701. Then the walls should be mudded out (or boarded) and waterproofed.

The fact that California uses hot mop is no really a big deal. it is a primary waterproofing membrane.

In California they build most of there showers wrong like the rest of North America.

There is no codes that say you must waterproof your shower. There is little to no inspections to check up on you. So - building your shower you can do it the way you want it done. Pick a specification from the TTMAC or TCNA or let your builder do it.

Remember the odds. About 9 in 10 showers are built wrong - maybe yours will be the lucky one!

The thing to consider is time. How fast can you waterproof with a mudded out wall verses cement board. That is where cement board excels in the Which is better debate.

    Bookmark   March 20, 2015 at 5:57AM
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