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Luxman 04-15-2021 10:21 AM

Master Bath Complete Tear Out
5 Attachment(s)
Hello All,

Like many I found my way to this great resource while researching my own job. Thanks for being here! As mentioned in the thread tile I’m remodeling our master bath, removing tub and stealing a little extra space from a adjacent hallway closet giving me more space for walk-in shower. The home is built on a concrete slab. The desired layout dictated that I relocate/move the tub (now shower drain) and toilet flange about 15”.

That’s been done and I ended up removing a large section of the old cast iron mainline and tying in PVC. All remaining lines up have also been changes to PVC including vent to roof. This has been inspected and passed by the City along with electrical rough-in. I was present for these and the City Inspector seemed to be very thorough.

My question or concern comes from the shower area build and of course it’s water proofing. The area framed out including wood frame bench and curb. Shower pan pre-slope established and Oatey 40 mil pan liner installed. Aquabar B has been stapled to the studs and Hardie Backer on top of that. The Hardie Board seams have received mesh tape and joint compound, they used VersaBond Fortified thin set. All screws were also covered then all surfaces treated with RedGard.

The installer has planned to have the Hardie Board buried in the deck mud and after discovering this I told him this was not correct. The deck mud should be done first then the Hardie Backer which should then be at least 1/4” away/above the mudded shower floor. So so tear out and redo needs to happen and this being the case I thought this a good opportunity to post here for comments and advise.

BIGPHIL 04-15-2021 12:08 PM

First, welcome to the board, Don! I'm going to let others answer about your question regarding removing the HardieBacker board and general construction of the pan liner.

I actually have a question for you...what is the second Grohe Rapido SmartBox going to be used for that is so high on the wall? I also find in interesting that whoever installed the lower SmartBox kept the second mounting plate attached. The directions from Grohe leave a lot to be desired and are confusing to say the least, but that second plate is to only be used when mounting the SmartBox from behind the wall. In an open stud bay rough-in like you had, the plate should have been removed. It is NOT for depth guidance...the white lines around the circumference are for that and provide you with 1 3/16" of area in which your finished wall is to fall within. In your picture with the RedGard applied, I can still see a blue square which indicates a problem to me. I see no way they could have properly applied the sealing collar that comes with the SmartBox in the manner in which they've installed the unit. That, coupled with the fact that the second flange is still on the SmartBox with no obvious waterproofing, water may certainly find its way down the wall and end up behind that area.

Another thing...the bench looks dodgy to me. From the second picture it looks as though there is no solid surface under the pan liner which would allow water to pool there. I can see obvious dips where the liner is falling in-between the framing of the bench in the second picture. Is it even slopped to drain at the required minimum of 1/4" per linear foot?

Luxman 04-15-2021 12:27 PM

Hello Phil,

thanks the reply, I’ll answer the bench question first, the bench top does now have a piece of plywood on its top. It’s also pre-sloped.

The upper Grohe rough valve a Grohe Multi-Function rain head, inner and outer spray patterns can be turned in independently of both at once.

As for the lower valve you are correct, Grohe’s instructions are pretty crappy. As for the mounting square you refer to I will research and bring this up to the GC now. Things like this are exactly why I (and I assume others) make these threads to start with thank you.

cx 04-15-2021 04:23 PM

Welcome, Don. :)

If your contractor intended to waterproof the interior of the shower using the direct bonded waterproofing membrane (RedGard in your case), he should not have installed the Aquabar behind the backer board. This is especially true when using Hardiebacker, which is a Fiber/Cement board rather than a real CBU (ASTM C1325). Trapping moisture in the Fiber/Cement board between two vapor retarder membranes is not a good idea.

How does he intend to finish the curb? Hopefully not the same way he finished the bench.

My opinion; worth price charged.

Luxman 04-15-2021 06:00 PM

Hello CX,

yes, I understand no need for both Aquabar and RedGard and is therefore not correct. Having spoken to the GC it’s seems he’s subscribed to the idea of more is better without understanding how products work or enter act with one another.

Having done some reading on Hardie Backer seems what’s produced today might be different than what was available several years ago. I see the “moldblock” printed randomly, just marketing BS or?

The shower floor including curb is to be floated. I had already discussed and was told they fold wire over the curb profile and float it along with the pan. I was also told it will have the required slope inward toward the shower floor.

Lou_MA 04-15-2021 06:15 PM

CX - I’m drawing a blank. How should benches be handled with a pvc liner?

cx 04-15-2021 06:36 PM

As well you might, Lou. There really is no good way to handle a wood framed bench in traditional shower receptor construction. Most commonly a liner would be installed, a moisture barrier installed on the walls, the walls would be mudded, and a masonry bench would be constructed within the confines of that waterproof envelope. Same could be done with CBU walls, of course.

My opinion; worth price charged.

Luxman 04-16-2021 08:58 AM


having a little trouble navigating ASTM C1325, not finding verbiage that clearly states this. It’s likely I’m not finding the correct reference or missing something else.

Luxman 04-16-2021 09:43 AM

So how does this tie into the conversation, if at all?


cx 04-16-2021 10:02 AM

Don, that ties into the conversation by pointing out that Hardiebacker is a Fiber/Cement board (ASTM C1288) rather than a Fiber-Mat Reinforced Cementitious Backer Unit (ASTM C1325). The two are commonly lumped together when referring to CBUs, but they are different and the difference is even recognized in the NTCA's published methods of using CBUs in shower walls.

My point was that the accumulation of water within a C1325 panel might do nothing at all while the same accumulation in a C1288 panel might cause deterioration due to the presence of the organic fibers. Do I know that for a fact? No, I do not, but I'm always inclined not to create environments where moisture is trapped anywhere in a residential structure, and especially when the application is better served and the construction is easier and less costly without creating such environments.

I am aware that James Hardie now makes a panel they say is waterproof. I've not seen it or touched it nor do I know anyone who has, so I can't comment on the use of that product and I don't think that's what was used in your shower.

The world is free, of course, to take my opinions with whatever number of salt grains they might think appropriate, eh? :)

Lazarus 04-16-2021 01:42 PM

I'm just a tad curious as to why you have a door, apparently going nowhere in the back of your shower as seen in the first picture.....:scratch:

Luxman 04-16-2021 02:23 PM

Hello CX,

please don’t take my comments/question as not trusting your knowledge or advise. I’m just trying to understand as many aspects as possible. As I mention above I was/am having trouble finding (let alone making sense) of ASTM C1288 or C1325. I do have a copy of the TCNA Handbook, to your knowledge is this any of this sort of thing mentioned in this handbook? I did find the section that specifies how different types of wall boards should or shouldn’t penetrate the deck mud.

ss3964spd 04-16-2021 02:39 PM

I'd guess that's a closet/linen closet, Laz. ;)

Luxman 04-16-2021 02:42 PM

Laz, ever hear of the Winchester Mystery House? LOL, that space was a rather large walk in hallway closet that was accessed through the door you see. We’ve stolen some space for the shower and making that a smaller closet, 24” deep. Hopefully these additional images will help.




cx 04-16-2021 05:56 PM


Originally Posted by Don
please don’t take my comments/question as not trusting your knowledge or advise.

Don, you needn't apologize for questioning any advice given you by people not known to you who you've met on an Internet site, including this one. We do pride ourselves on giving out sound and correct advice, and when any one of us strays from that path, one or more of us will be quick to point it out. In my particular case, you can count on several people knocking one another down to do so. :D

You don't need to understand everything in C1325 or/and C1288, you just need to know they're different and the different products tested under those standards behave somewhat differently. The true cement boards (C1325) have no organic materials in their core constructions. The Fiber/Cement boards, as the name implies, do have such material in their core. For most applications you don't care at all about that portion of their construction. For some applications, those involving moisture, exterior installations, and freeze/thaw conditions, you might.

The shower construction methods published in the TCNA Handbook are a good example of where the difference is worthy of consideration. You will not find any discussion in there about sandwiching various CBUs between multiple waterproofing or vapor retarding membranes because that comes under the heading of "why would anyone wanna do that?"

What you've got may or may not cause you any problems. If it does, you'll not likely know for years. Maybe a lot of years.

My opinion; worth price charged.

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