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-   -   Tub to shower (https://www.johnbridge.com/vbulletin/showthread.php?t=129477)

gcc 07-10-2020 06:21 PM

Tub to shower
Hey all,

I’ve been searching but just can’t seem to find the answer so I apologize if I am asking something that has already been asked numerous times. I’m going to remove a tub and just make the space a shower. It’s Florida, slab on grade. Just a few questions while I am planning:

1. Does the Schluter offset tray fit this scenario? The drain will be really close to the wall since it is for a tub at this point. I am wondering if the offset tray would work well in this scenario and allow me to keep the drain in place as is.

2. For the curb, if I don’t use the Kerri curb, can I make the curb out of 2 x4’s tapconned into the slab, then putting cbu over that and wrapping it in Kerdi? Just wondering.


jadnashua 07-10-2020 07:43 PM

If the drain will line up, yes to both of your questions. In fact, you can use drywall on the curb instead of cbu if you're going to wrap it with Kerdi if you prefer. Or, build the curb out of pavers, then wrap it with Kerdi...probably better over a slab than wood. Or, use some Kerdiboard. You can laminate sheets together if you wish and use that.

Lefteris 07-10-2020 08:00 PM

Hey I'm on a pretty similiar boat. Any reason you are looking at kerdi over the preslope, cement board and 'redguard' method?

gcc 07-10-2020 08:25 PM

Only reason is the shower tray. Doing a slope that long across the shower seems intimidating. I’d be tempted to move the drain to center it and that means busting up concrete. Still, I haven’t decided yet.

I’d really like to just do one slope and use redguard on the pan as well, but I’m not sure how to connect the drain in that scenario.

Sent from my iPhone using Tapatalk

Lazarus 07-11-2020 08:53 AM

Unless you are using a linear drain, "one slope" isn't gonna work. Best result will be to move the drain to the center, pack one mud bed and Kerdi the whole thing.

Build the curb out of brick or masonry and you can extend the Kerdi up and over it.

gcc 07-12-2020 08:51 AM

So there is no way to use the schluter offset tray in this scenario? I am sure there is a box out for the tub drain and I know I'll have to convert to 2" pipe. I was hoping to avoid busting out concrete but if I am going to bust it out I may as well center it. Was hoping to avoid that.

I may still go the schluter route on this. By the time I end up framing out a bench and a niche, and a curbs, it may be a whole lot faster to use the schulter products and get it done that way. The last two projects I did were done traditionally - one was a shower and one a tub, both used poly behind cbu.

If I go Schluter/Kerdi, is there ANY benefit at all to keeping it cbu instead of drywall? In my head, if there is a leak or even if some water somehow finds its way back there, cbu would be better. But drywall would be so much easier to work with and logically, if it is waterproofed, it should be fine. Kerdi board would be great but a 4 x 8 piece of drywall is around $13 down here and a 4 x 8 piece of kerdiboard is around $100, so I am not doing that. So any benefit at all in keeping it cbu?


cx 07-12-2020 09:36 AM

Greg, I would always recommend centering your shower drain. You'll see all the benefit come time to tile the shower floor.

I would also recommend you make your own shower floor of deck mud to precisely fit your shower footprint and drain location and have the proper slope with a level perimeter.

Fearing drywall behind the direct bonded waterproofing membrane because you might one day have a plumbing leak would mean you'd need to install CBU in all the walls in your house where any plumbing is installed, including behind your refrigerator.

If it makes you more comfortable to use CBU behind your Kerdi, by all means do so, but it's not necessary.

My opinion; worth price charged.

gcc 07-13-2020 06:36 AM

Thanks CX - My hesitation for drywall may also be my own fear of screwing something up and thinking that CBU would be slightly more forgiving if any water got through :) But that's probably foolish thinking.

A few plumbing questions:

1. About moving the drain...I assume I would cut the riser pipe as low as I can in the box out, put a 90 degree fitting on it as low as possible to be able to put a horizontal straight piece of pipe into it, and then another 90 where I want the drain to be and put a riser on it. At some point a fitting of some kind would need to take it from 1 1/2 to 2 inch pipe. If that sounds right, does the pipe need to slope at all downward from the new drain riser pipe back to the original placement? My concern would not only be the height but also the fact that it would put the new riser pipe at a slight angle, making it impossible to make the drain level. I'll know more after demo, but just want to be prepared.

2. When it comes to relocating supply pipes, is there anything wrong with transition from copper to cvpc? It would be easier to sweat on a transition piece and then just plumb out the rest in cvpc for me. Or is this just personal preference?

3. The reason I ask number 2 is that the toilet is on the same wall as the current shower / tub plumbing. I don't really want to put the bench on the same wall as the plumbing, but if we put a bench on the other side, that leaves very little room for entry into the shower. (Between toilet and bench) We could always go with the triangular bench but was trying to do one that spanned the width of the shower. Any thoughts?


cx 07-13-2020 07:28 AM

1. Greg, the only place where you can reduce from a 2" drain to a 1 1/2" drain line is at the shower drain fitting.

While it's not generally necessary to change from 1 1/2" drain line to a 2" drain line for a tub to shower conversion, it's a good idea to do so, 'specially if you're gonna move the drain anyway. To do that you must replace the 1 1/2" drain line all the way to wherever it connects to the larger drain line in your system. You must not reduce the drain size anywhere along its course.

Regardless whether you change the drain pipe size, you want to remove the existing P-trap and put a P-trap immediately below the new drain location.

All drain pipe 2" and smaller must slope a minimum of 1/4" per foot along its entire course. Your riser to the drain must be perpendicular and you should have no difficulty making that happen while connecting the trap and riser to the horizontal pipe.

2. Better you should continue the plumbing in copper or PEX, but you could change to CPVC if you wanted and your local code compliance inspector agrees. It's still legal as far as I know.

3. Don't understand the problem.

My opinion; worth price charged.

HooKooDoo Ku 07-13-2020 09:16 AM

Sounds like you need to make sure you've checked with local codes.

"Typical" residential building codes allow tubs to have a 1-1/2" drain, but require a 2" drain for a shower unless the shower head can not produce a flow rate greater than X gpm (and it's been too long since I worked on my bathroom to recall what X usually is for building codes).

So as CX points out, if your building codes require a 2" drain for your shower, you'll have to make the drain 2" from the shower to the main drain line.

{I recall this building code requirement in general because my contractor stubbed in a down stairs bathroom with a 1-1/2" drain, so when I went to finish the bathroom myself, that building code requirement caused me to install a tub/shower rather than a shower only. I seem to recall the reason for the difference had something to do with the fact a tub has the volume to allow water to accumulate and then drain slowly, where as a shower pan doesn't usually have the volume to allow water to accumulate and drain slowly later.}

cx 07-13-2020 09:58 AM

Don't think you can exceed the 1 1/2" drain capacity with a single shower head setup these days, Joseph. See my warranty information below.

OP still wants to verify the requirement with his specific code compliance official, though.

My opinion; worth price charged.

gcc 07-13-2020 02:03 PM

1 Attachment(s)
Hi all,

Thanks. Code allows for 1 1/2" trap but a 2" drain, if I am reading the attached section from the plumbing code correctly.

Just so I am clear....I need to dig out the old P-trap for the tub no matter what. Then evaluate if that is where the tie in is to the main drain. If so, I can switch to 2" pipe and run 2" pipe to the new location, with a 2" P-trap. If this isn't where the tie in to the main drain is I would have to use a coupler to attach new 1 1/2" pipe to the pipe that is there and run it to a 1 1/2" P-trap at the new location, and use an adapter for a 2" riser pipe. Is that correct?

I guess I am fuzzy on what I will find when I dig up the existing 1 1/2 P trap for the tub.


jadnashua 07-13-2020 05:57 PM

In many places, they want buried pipe to be at least 2"...so, if you're lucky, you only have a 1.5" trap for the tub, but it changes to 2" right after it. You won't know until you dig into it a bit more.

gcc 07-16-2020 10:43 AM

Makes a lot of sense now that I went to HD and looked at the P-trap. I have to physically interact a lot of times to finally get an understanding. Thanks!

A few questions as I decide on the construction method. The shower will have a bench of some sort - possibly a rectangular bench. The plumbing for valve is on the same wall as the toilet - it's a typical toilet next to tub placement with it being a few inches away. There might be a small knee wall there as well. Also, going to have a few niches. Because of those I'd like a surface membrane instead of poly behind the cbu. To be honest, using kerdi board is almost the same price as using drywall with kerdi membrane by the time you by the membrane around here, so I may go that route. Other option is redguard or aquadefence over cbu in a traditional receptor.

Since I have to move the drain I can try to center in in the shower. If I use the kerdi tray and get the 38 x 60 tray, I'd have to trim that down or I could just do a mud bed. But if I go that route, I may as well save the money and do a traditional receptor and redguard the walls and save some money. So as I decide, I am wondering a few things...

1) If I do traditional receptor with redguard on the walls, could I frame the bench before I do the mud bed out of wood and attach to wall framing/slab, then redguard it? (SOG foundation) Would I just run the liner up to the same height as I do the walls? Or is it necessary to to do the entire pan first and then build it out of cement block later? OR would either work?

2) The curb - The liner is supposed to go over the curb. If I am redguarding the entire shower but have a traditional receptor, is it still required to build the curb using lath and mud over the liner? I want to say it is, but want to confirm it. I saw Sal Diblasio uses cbu over the liner at the curb. If it is redguarded and seamed, I can see how it could work, but I'm inclined to think I would need to do it the old fashioned way with lath and mud. Please correct me if there is an easier way.

3) SInce it is a slab, do I need to put down Sil Seal or tar paper under any framing that touches the slab if I use regular 2 x 4s? It is on grade, not below grade. I'm thinking of using a few tapcons for this.

4) Thinking of kerdi....I'm sure it would be better to do a mud bed for the receptor, but just so I know, if I were to use the 38 x 60 kerdi tray and cut it, how off would the line around the shower really be? It's a tub to shower conversion. I can't really push the width of the shower much further than the tub is now, which is a total space 32 inches, or it starts to encroach the toilet. Leaving a 4 inch curb, that would mean the tray would be 28 inches - cutting the tray back by 5 inches each side running that direction. If I shorten the 60 inch length by about a foot - or 10 inches - by adding a 10 to 12 foot bench - that would make it about 48 or 50 inches, that means I am cutting about 10-12 inches off that direction as well, or 5-6 inches on each side in that direction. Assuming I move the drain to the center of that area, would it be pretty level and would that work?

Thanks all,

cx 07-16-2020 01:21 PM

1. It is theoretically possible to do a wood framed bench that way, but after you've tried it you'll understand the theoretical part. And you'll see why folks elect to use the "monument bench" method when making benches in traditional shower receptors. Or using something like the Better Bench.

2. One of the things Sal gets wrong. There is no acceptable method of using CBU to cover a curb in a traditional shower receptor. None.

3. Yes.

4. I suppose there are folks who can see the rationale for going to the trouble to near-perfectly level a subfloor, buy a very expensive foam shower tray that has insufficient slope to begin with, cut off and throw away 35 or 40 percent of it to make it fit the shower footprint and drain location, end up with a shower floor that does not have a level perimeter or sufficient slope and call it easy and convenient. I'm just not one of'em. :)

My opinion; worth price charged.

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