Curbless Shower On Concrete Slab - Remodeling


Ok, this is my first post so bear with me. I'm still a little new to this whole internet as a means of having professional questions answered hah.
I'm a tile sub on a remodel in Houston, Texas, the client is having a bathroom remodeled. Part of the remodel is taking an existing coffin shower and creating a curb-less shower in it's place. The shower is going to have a 1/4" slope per foot spanning 60 inches. Here is where the question comes in. The sub doing the shower work is going to cut the slope out of the foundation, I've never seen this done on a on commercial site. Is this the normal way you would go about putting in a curb-less shower? It is by all means easier on me doing the tile work to have it done this way but the residential foundation is only 6 inches thick on a single story home like this.
I just don't want an inspector to come through here and say it isn't up to code then the contractor or owner expect me to redo all the tile.
Any help is appreciated!

Sounds like you're on the right track!

Your post was very helpful!

Do what Tom says, then.
- Bob

I'm sorry for asking but I'm curious. What kind of problems could arise from cutting the slab instead of refilling it with the slope? Would it be a problem structurally or a code problem? I know code is different everywhere but you're welcome to chime in with hypotheses anyway.

Do you know what style drain is being installed and its location relative to the existing? Most cureless showers are a single slope at ¼" in 12". If it is going to be a new lineal drain a replumb will be needed, might as well cut the floor.
You can mortar a pre sloped pan or a dry pack over the existing. Problem I see with this will be the drain.
If it is a multi slope, the floor can be ground to meet the (assumed) center drain. It will still need to be ¼" in 12".
No matter how it is done, make sure you waterproof the pan.

No code issues either way that I know of as long as the pan is waterproof and passes a 24 hour test.

Good point, it's going to have a linear trench drain at the wall of the shower under the fixture.

Make sure it isn't a post tension or pre-stressed slab before cutting into though.

I doubt with a house this size (1500 sq ft max), and age is prestressed. Don't those have service holes usually?

They have some seriously tensioned cables in them. I've seen one cut that rolled back right through the concrete. Lucky no one got killed.

Usually there is an stamp embossed into the garage slab if it is a PT slab.

Forgive me if this is OT, but why would a slab have tensioned cables in it$ I'm not familiar with that.

I've never really seen it done in residential construction, although calling a buddy he says that it's actually fairly common. With Houston having shifting clay soil, putting tension on the concrete will help prevent it from cracking.
I'm not really well educated on foundations, but it is very interesting.

Whoa guys... there's no reason to grind the slab, or repour the slab or even use any concrete at all.
I've done several curbless showers and there are systems that you can buy to do this. The one I use is rather expensive because it has a stainless steel drain which can be as much as 6 feet long. The slope is created by a pre-sloped honeycomb mat that takes less than 20 minutes to install. You simply cut the mat, fill it with thin set, then cover it with Schulter Ditra or equivalent . The slope is perfect every time and there is no grinding or chipping or anything. The drain comes with a piece of water proof fabric already attached so the floor materials simply overlays.
You will however have to provide for the drain and of course the waste pipe, but the shower floor only takes minutes. I don't use Ditra very often because the expense and because I just don't care a whole lot for it, but inthis application, it's mandatory to cover the pre-sloped mat.





Here's a video that shows how it works.

I would not remove part of the slab for this installation. Though I have never worked in Texas, I would expect that this is a monolithic slab/footing, and as such the slab can be considered structural.
Why not just over lay the slab to get the elevations/drainage you need?

Not a single one of these guys would approve of you shaving an inch and a half off of a few floor joists to make this work on the second floor of a home, and yet from what I read....It's ok as long as it is not a post tension slab.
Treat the slab as an area not to be disturbed. I'm sure it is easier and faster to build upon it, than it is to grind it down and come back up.

How would you go about putting the honeycomb down when the floor is on grade with the drain? Is it all incumbent on having the drain be on the "front" of the shower?

As the tile guy, I would recommend not doing that, first, the bathroom isn't that big so you would notice the slope from the door to the shower, secondly, there is a small room with the toilet in it that would need to either be raised to grade, or have a slope in the entrance. This would all be difficult with the type of tile they are using.

I'll do a seperate thread on how to build this shower. There are some things you may want to know so you don't make some of the mistakes I made.

Please do! I'm wondering if something like that would work for this job since it kind of only has 1 glass wall, it's a really open shower concept.

Overlay pre slopes were mentioned earlier, with their pitfalls and considerations.

I have no problem dropping the depth of a floor joist. Sister another next to it, happens more often than you think. It's the ones where no thought is pout into the structure that cause the problems. Just like when joists get cut moving a toilet, just crappy workmanship.

There are two different ways to drain a curbless shower. One, is to cut down against the back wall so that the floor slopes away from the glass and second is to slope the floor toward the glass without cutting out ANY floor.
The key is the drain. When draining back toward the glass without cutting out the floor, the drain HAS TO BE long enough to reach from wall to wall or water will bypass the drain and run out on to the floor on the ends.

Ok.. remember now... this thread started as a question about a slab, so when I'm answering questions it based along that line. If you have a joist system, you have more options, but if you start cutting joist, then you have created a LOT MORE WORK than you have to...
Let me explain.... If you start cutting down on joists, then you have to make each joist exactly like the next one and so on, then they have to all be sloped exactly the same. If you want to use a presloped mat where the high side is at the glass and it slopes toward the wall, then you must "build up" the non-shower portion of the bathroom floor. That's easy, just use OSB or Plywood. That way, the high side of the presloped mat is at the glass and the drain is against the wall.
When the drain is at the glass, it's harder to build.

Post tension foundations are very common in residential in north Texas. Actually, probably more than 90% of new residential construction is post tension here. I've drilled into a couple of cables and it's kinda hard to feel the "bump" over the rotary hammer drill action when they let go. Perhaps that is because the cables aren't really stretched like rubber bands. 30,000# on a 1/2" cable 100 feet long only takes a couple of inches out of the cable. Not a big deal. The PT supplier comes out and chips out the fixed end. The "pull" end breaks out at the other end a couple of inches. They drill out the pull end so new wedges can be inserted, swab out the tube, re-grease it, slide a new cable in (repair cable has a slightly different head on it) and pull it to about 75%. The next day they come out and do a final pull.

What IS explosive is a "blowout" on an initial pull. Those aren't pretty. Usually the result of lack of proper concrete vibration at a cable bearing point.

This is what the shower should look like, except there is no wall to the right, that ill extend another 3 feet and have a clawfoot bathtub

My joist response was to a post by "tgeb" a few up.
I see no problem with making the joist the same. I do it all the time in many applications. I know I post pictures of a lineal install on a joist system.
Any grate receiver will cause the area outside the shower to need to be raised to meet the height of the receiver lip plus the grate. As long as it does not affect other floor elevations, no big deal. If it does, the install needs to be rethought.
No matter what you have to cut the slab at some point to install the grate receiver and relocate the drain. Question is, is it easier to remove a 3x5 section and rep our or patch in the trenches?
I do know of the "web" you mention. Tile Shop? Only difference if I would use drug pack instead of thin set to fill between. Thin set is not made to be built up to the thickness the "web" requires.

Bingo... and therein lies the mistake that I made in the shower that's in the pictures posted in this thread. When I did this shower it was the first curbless that I had done and I thought I had it thought out and planned well, but when it came time to install the glass, I realized that I had a potential problem. When water runs down the glass, it hits the shower floor on the non-sloped side of the drain. The glass is flat on the floor and sealed so it's not a problem there, but the door created a whole new challenge. Water ran down the door, landed across the drain and wanted to run out into the middle of the room.
To solve this I installed a small silicone sweep on the bottom of the glass door and it was just enough to save the day. This particular shower was in an extremely small bathroom.... probably the smallest I'v ever worked in, but the client was more than satisfied with the look and was ok with the fact that she would have to replace the sweep every couple of years when it wore out.
The next curbless I built was alot deeper than that 28" shower and I drained it to the back wall. To do this, I simple added a 3/4 plywood to the rest of the bathroom floor to build it up so the top of my sloped mat was level there, and sloped downward to the back of the shower. I did this specifically because I didn't want to have to cut down the joist.
READ THIS---> These drains require that you cut out a section of joist across the entire length of the shower. If you are cutting out part of the joist AND cutting down the joist, you potentially would have to build a sub joist system under the existing joists to maintain proper support else risk a saggin floor or possibly even joist failure.
When in stalling a curbless using sloped mats, it opens up a whole new realm of possiblities. WHY? Because the floor is even from side to side and you can use any type of tile you desire. There are even grates with a tile tray so you can cut tile to fit in the grate.

Here's the problem with this shower... for there to be slope, there has to be a drop off from the glass to the drain, so if there is no wall to the right as you said, there there will be ankle breaker drop off on the other side of the shower too. I can't imagine that I'd like something like this if it were my bathroom....
... or am I hearing you wrong?
And by the way. When I first looked at this picture, I thought the drain extended out from under the glass, but when I blew the picture up in Photoshop, that's an A/C register.

Actually the slop extends to the showers entire length, I guess anything after the glass isn't considered "shower" perse but it makes the slope much more gradual. *EDIT I see what you're talking about, I meant the right of the photo, not the shower itself, there is a wall to the right and glass to the left.

Sound like there is cause for your concern there.
Grinding the slab is done all the time or even demo'ing the slab is done but never the foundation wall without having a permitted plan to address the possible consequences of cutting into foundation.
I am not of much help but what the hell? I am edging in to 2000 posts.

Thank you for the quick reply! I'm nearly positive that if he ends up going this route he will get a permit. The contractor is someone I've known for a long time and have never see him not have proper permits on anything he puts his name too. He's a real by the book ass kicker. I suppose I should leave that up to him since I'm just the tile guy, but what's the harm in asking for a few other opinions?
Anywho, the shower actually won't be on the foundation wall, it will be about 3 feet from it on the highest point, and 8 feet on its deepest point. Anyone else done something like this?

Cut the floor out and replace the concrete with the proper slope. This will allow the drain to be relocated/run properly.
You must waterproof the new "pan".
Don't cut the foundation.

Agreed. KSavar, when you say "foundation" in your original post, do you mean "slab" (rather than foundation wall or footing)?

Forgive me, yes that is what I meant.

Way to go!

I just finished putting in a curbless shower on a concrete slab. It used to be a tub. I used a $15 circular saw from Wal-Mart and a 7" diamond blade. Took me about an hour to cut 1.5" deep lines in the floor every 1 inch. Took a demo chisel from Harbor Freight and the pieces came out like nothing. I cut another set of lines in the middle about 6 wide in the center of the drain line and about 25 inches long. Used the demo chisel and then a sledgehammer to move the drain line. Put in a new drain and filled up the cut with regular quickset concrete. Mixed up two bags of SpeedSlope mortar and had the slope done. I keep the SpeedSlope in the freezer and use ice cold water as the mix. If not it sets up too fast. I went from on-grade 6" thick slab to sloped slab and centered drain in about 3 hours. I did some sheetrock work then came back and RedGarded the floor and walls. It's not hard to do and the SpeedSlope is the key. If you use regular sand mix the RedGard folks say you have to wait 28 days. This way the slope is ready in 2 hours.  I used porcelain tile and epoxy grout on the floors and walls. I can guarantee that shower is not going to leak. 

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