Bathroom Number the Second One

[Platypus]

Hello again,

First, another final thanks to everyone for all the advice on bathroom number the first one ("Bathroom Fiasco"). It came out very well, and is holding up perfectly.

Now, however, break time is almost over and I'm beginning to plan the second one. First question comes up immediately:

I'm planning to build a seat in the shower this time, and I've read the thread about how to do this -- it goes completely inside the cement backer and pan membrane... got it. However, I do have a question about the instructions given by the legendary founder:

JB indicates that as you build up the "block" for the seat, you fill all the voids with deck mud. I want to do it slightly differently, however. Please tell me if I'm going to do something naughty.

I want to use cinder blocks for the bench seat base The bench will be 16" deep, approximately 37" wide, and about 18" tall. As you all know, cinder blocks are 16" long, which is a perfect size for this. I can make two rows high and fill up the spot in the stall almost perfectly. Then cap with a concrete slab and cover with tile as normal. All of it bound together with mortar, just as you would do with a masonry wall, only two blocks deep instead of just one.

I do _not_ want to fill the voids in the cinder blocks unless I have to. Here's why: Filling the voids will create a thermal mass of several hundred pounds. This will serve to cool off the shower space pretty much continuously, and the seat will always be cold. Mrs. Gerry won't like that at all, and Mr. Gerry isn't crazy about the idea either. You'd have to run hot water in there for hours to warm up that much mass. So I'd like to leave the voids unfilled. Is that going to create a problem? If there's nothing in there for mold to grow on, why wouldn't you just leave the voids empty? I will even spray it all down on the inside with a generous borax solution before I seal it up.

So, is it going to cause tears and agony later on down the road if there is air space inside the bench?

[Bodie Powers]

I'm wondering if applying Kerdi Board to the bench seat would work? It does have insulating properties and Schluter shows it being used in a bench application. Here's a link: http://www.schluterkerdiboard.com/ You might want to call Schluter tech support with questions.

[Davy]

Hi Gerry, I build all my shower seats out of concrete blocks and fill them like JB talked about. I also mud the top and face to make a flat tile surface. Not sure how you will do that without filling the holes. I'm not sure how much difference the temp will be, still a lot of concrete there.

I wonder if you can use Kerdiboard or Wediboard for the seat. Maybe someone else will chime in about that, I'm not sure.

[Lazarus]

Seems to Moi that the cinder blocks will reach room temp and be no colder than anything else in the room. Built many of them and never had a complaint.

[Davy]

I was thinking the same thing, Laz. Maybe it would be cooler if was installed against an outside wall. But, looks like the hollow blocks would be cooler against an outside wall too.

[Platypus]

Right, I guess I should have just asked why the monument is supposed to be a solid block, or to put it in negative terms, why can't it be hollow?

What about filling the voids with some sort of foam? Maybe the same kind of stuff that the Noble bench blocks are made from?

[Davy]

From what I read, there's nothing in concrete blocks or the mortar to allow mold to grow. I don't know if adding foam would change that. As far as the temp goes, I've built hundreds of concrete block shower seats, even in steam showers where folks sit for a while and I've never had a complaint about the seat being too cold.

[Platypus]

Decided to leave the bench un-filled. Will soak the inside cavities with strong borax solution a and hope for the best. I don't care about the thermal mass anymore, but I really just don't want it to get waterlogged and stay that way, and I think a hollow bench will drain faster if any water gets in there (and it will, because it's not waterproofed). Would love any further feedback about this, however. I'm stubborn, but not stupid (or is it stupid, but not stubborn?). So far, I haven't gotten a good reason to fill it with mud, other than "that's how you do it". Hardly compelling.

So, moving on:

Next, I am cosidering how I will do the pan. I have the benefit of a concrete slab, so i can get started without any sub-floor foolery. However, there is a good 4" gap/leave-out around the drain pipe that i will need to fill after I connect the drain.

I still can't decide whether to go with traditional membrane and two layers of mud, or try a liquid waterproofing over a single slope. I used RedGard before, and it worked well, but that was in a tub surround, and a floor is a little more "scary". Would use fabric reinforcement if I go this way, of course.

However, I don't quite understand divot drains yet. I've seen pictures, and they look simple, but there's another consideration: I want to try a concealed drain. The Missus has already picked out the floor tile: one-inch brown stone squares. I like them too; they're a nice non-slip surface and should make the layout really easy. These also lend themselves to a concealed drain... Oh, boy, heeeeeeeeere we go.

I was thinking of just getting a 4" x 4" x 1" thick (or so) block of granite and putting some holes in it and then bonding a small patch of the floor tiles to that. I would need to leave an appropriately-sized depression in the floor for this, of course, and thought I would just make a blank out of wood that is a little bigger and mud it right in, then remove it when the mud dries. This depression will need to be above the waterproofing, of course, with a lip or ridge that will keep the fabricated stone "grate" from putting pressure on the plumbing too. I can figure all that out, but I'd like some input from someone who's done a hidden drain as to the pan considerations and anything else thay be less than obvious.

Or, is there a special kind of drain made specifically for this, and if so, what is it called (and can I have a brand name or two, please)?

Does this lend itself better to a membrane or divot pan system, or does that have any impact? Is this the right way to do a hidden drain?

Thanks,

(edit) - Now that I think about it, I think this will probably not work. As the granite rattles around from being stepped on, it will wear on the bottom and sides of the depression. This could eventually result in a leak. I left the post as-is, however, so that others can learn from my stupid idea. Would like to hear the proper way to do a hidden drain.

[Platypus]

here's a pic from the first remodel. This one shows the space, the plumbing and framing "challenges", and the leave-out. I'll describe the space before I ask for some advice. Many of these questions concern space; there's not much space to work with, the room is 5' wide and that area that is bare is about 32" deep, can be made about 40" at most.

Now then:


1) On the left, there is existing plumbing, including the vent pipe for the terlit. It's hard to see, but it's right behind that stud, above where the gap in the sill plate is. It's exactly where I wanted to put the new valve for the shower. Dead center exactly.

2) In the middle of the floor is the existing drain, and a generous leave-out.

3) Off to the right, there is a chase, and some old plumbing in the back right. That's an exterior wall at the back of the chase. That's keeping me up at night.


Taking these in order:

1) I'm most likely going to have to build out the wall on the left, in front of the toilet vent tube, by about 4" to give me room for the valve and plumbing. Actually, I don't have a question about this... there's really nothing I can do about it. I don't like it, but that's the way it is.

2) the leave-out is about 8" deep, and about 3 to 4" around the pipe on all sides. Can this be an advantage if choosing a divot drain? In other words, will this allow me to make a very thin pre-slope? The divot could possibly be a little below the grade of the existing slab? I want to keep the floor of the shower as close to the level of the rest of the room as possible. Just because. This also makes me lean toward a hydroban or redgard waterproofing instead of PVC membrane.

3) I'm planning to remove the chase and cap off the plumbing there. Then, I'd like to install a row of glass blocks high up in the exterior wall. I have brick veneer. That's also where I plan to build the bench in the shower. I'll have a professional mason cut the brick veneer and install the glass block. Is it OK to put CBU up right against the exterior insulation, or should I build out the wall -- put a second wall in front of this one? My concerns are freezing temps, and putting CBU right up against the insulation. There's a moisture barrier on the other side, between the brick and the insulation, and if I put one on the inside, then it will be a sandwich. However, even if I build out the wall, there's still nowhere for any moisture to go, although there will at least be an air pocket between the insulation and the CBU. I'm wondering if that's why the chase was there originally (they left the top open to the attic). What says the collective?

[John Bridge]

Hi Gerry,

You can route the vent around the shower valve and shower head using four large arc 90s and a few lengths of pvc pipe.

[Platypus]

Hi John (Mr. Bridge?)

I had actually already considered re-routing the vent, but was concerned that it would violate code, or it would just be cheesy.

Also, since it sits between two studs, and there's all that other plumbing, I'll like to put a horizontal member between the two studs because I can't put a stud all the way down to the floor. So I would need to reduce the diameter of the vent pipe for that. You can't see it, but it's 5" pipe... in a 6" plumbing wall, go figure.

Anyway, in the detour you describe here, can I also reduce the pipe to about 2" diameter for the new vertical section, so that I can have some room in the wall for a horizontal block or two?

[Platypus]

Poor form to bump, I know... but question 3 above is keeping me up nights. Anyone?

[Platypus]

Started back on this. The chase has been ripped out, and the old plumbing capped off. It's time to get back to work.

I still don't know how to work around or with the exterior wall. Should I install a sheet of 6 - 8 mil plastic as a vapor barrier? I'm still planning on building another wall in front of that exterior wall, but the two will be very close together.

With the plastic vapor barrier, will I still need to vent the air space between that and the cbu?

Thanks in advance,

[Platypus]

I'm prepping for adding a mud bed over concrete and started to scarify the concrete.

Wow, what a pain in the neck! Literally. And other places too.

The concrete slab is smooth like you would see in a garage. I started with an angle grinder and a 1/16" abrasive masonry wheel. Made a few cross-hatch cuts and started chipping away with a hammer and cold chisel. After an hour, I have about 1/4 square foot roughed.

There has to be an easier way. It would be overkill to rent a big gas-powered machine -- it's only about 15 square feet. Can I rent a small hand-held scarifier that will do the job faster than my angle grinder? Would one of the diamond wheels on my 4" angle grinder really make a big difference? I might qualify for a second mortgage to afford one of those, if it's worth it...

Better yet, do I even need to scarify at all? Could I just drive a bunch of masonry nails or tapcons in a grid into the slab, leaving about 1/2" to 3/4" protruding, attach a lath to the heads, and mud over that? I will scarify under the strip where I plan to pour a concrete dam, regardless of whatever I do in the mudded section.

Of course, I'd rather do the whole thing the "right" or "best" way, but considering the amount of work this is, I will settle for "perfectly adequate". After all, if it were a plywood sub-floor, there would be a cleavage membrane, which implies that the mud bed doesn't actually have to bond to the floor at all. A good bond would help me sleep better, but if nobody has ever heard of leaks from mudding over smooth concrete, then I will skip scarifying it. Gladly!

By the way, this will be a liquid-applied membrane, so the mud bed will be a full 1.25" thick at the thinnest point under the drain flange. I will install a lath in the center of the mud slab, just because.

Must I scarify the whole area?

Edit: Just saw another thread that mentioned Mapei Eco Prim Grip for tiling over existing tile. Would that work for prepping a smooth slab to accept thinset and then mud? I'm thinking if it will allow bonding on a vertical surface it would be good for this. Just want to be sure.

[cx]

Gerry, we can't see the condition of your slab, making it very difficult to give you any advice on the need for mechanical scarification. Bottom line, though, is that a clean, roughed-up surface is better than slick concrete. By far.

A diamond cup wheel on an angle grinder can make short work of scarification of a concrete surface in a small room.

If you plan a reinforced mud floor of a minimum 1 1/4" thickness, you really needn't prep the floor at all aside from laying down a cleavage membrane.

Is this part of your second bathroom project?