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Unread 08-22-2022, 06:57 PM   #1
pls
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Master bath on concrete slab

I live in Maryland and my son just bought a house in Houston, TX. House was built in 1962. They are wanting to redo the master bath. It is small and has a shower and no tub. We think the shower is in the original footprint. They are hoping to move a wall and make the shower larger. I have never worked on a house with a slab so I am going to start with some questions that will require educated guesses.
1 What might be under the current tiled shower floor? Could it be solid concrete sloped when the slab was poured or is it more likely a mortar bed?
2 Anyone want to estimate how much it would cost to move a shower drain say 18 inches?
All guesses welcomed
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Unread 08-22-2022, 07:32 PM   #2
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Welcome back, Phil.

1. More likely a traditional shower receptor if it's original to the house. Deck mud pre-slope (if done correctly), PVC liner, final deck mud on top with tile.

2. No idea. If it's not a post-tensioned slab, it's not a big deal to move the drain a little. There are situations that could complicate that - grade beams, lack of sufficient fall, etc.), but usually just a bit of brute force labor. I've always done that part of the job myself when required.

Your son is healthy and somewhat capable?

My opinion; worth price charged.
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Unread 09-06-2022, 10:28 AM   #3
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Thanks, I ran out of bathrooms to renovate at our house so going halfway across the country to help our son. The plan is to use a single mortar bed covered with a membrane. I have never made a mortar bed before so I would like to practice. So at my big box stores I can get Sakrete Sand Mix but not Quikrete Sand Top mix. My son can get Quikrete but not Sakrete. Are they similar enough that I can practice using Sakrete but use Quikrete on the actual shower? This is his first reno project so I am helping as much as I can to make it successful.
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Unread 09-06-2022, 10:49 AM   #4
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For your initial practice, Phil, all you need is the damp sand. You can make as many tries as you want with the same bunch of sand. After you've mastered the technique, you could make a real batch of mortar and make you a final example, if you like.

I can't say anything about the composition of the different manufacturers' Sand Mix. Only Quikrete available in my area. You'll just hafta wing it on that issue, or maybe somebody else actually knows and will stop by.

My opinion; worth price charged.
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Unread 10-05-2022, 08:49 PM   #5
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My son has started the demo and ran into something unexpected. The first picture where you see the concrete slab is where the vanity and built in cabinet were located. These areas are below the top of the tile by about 3.5in. Based on the pictures does this look like a mortar bed? The plan is to move the right wall about 2 feet out to make the bathroom larger and the shower along that wall. The shower footprint will extend into areas that are currently the tiled floor. Bathroom floor will also have new tile.
Any suggestions on how to proceed? Do we need to tear out the entire mortar bed and start over or is it possible to remove the existing tile and retile over the existing mortar bed?
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Unread 10-05-2022, 09:13 PM   #6
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That's interesting, Phil. Is the foundation slab in that room lower than in the rest of the house?

I quite commonly dropped the shower area in the concrete SOG when building houses down here (Texas), but never the whole bathroom, and I can't figure why a fella would wanna do that. Especially with the cabinet work sitting down on the slab and the floor raised that high.

If you don't remove the entire mortar bed, you're gonna have some cold joints wherever your new mortar meets the old, which is not such a good thing. Without knowing exactly what you're looking at and exactly what shape the new parts will be, I'd be inclined to say it's best to remove the entire mortar bed and make a new one to fit the new layout. That would assume that you want the new floor at the same height as the current one.

I'm sure the city of Houston would be happy to have the fill material to add to one of their flood control projects.

My opinion; worth price charged.
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Unread 10-06-2022, 12:14 AM   #7
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We've run into that many times where the slab was dropped in the tile areas. Most of the time they would drop it when a thick tile was going in, something like Saltillo. Or, if the tile is unknown at that early stage of the house and just to be safe they lower the slab so any thickness tile can be used. Since you're going to enlarge the bathroom, I'd bust it all out and mud it back, avoiding the cold joints like Cx said.
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Unread 10-06-2022, 07:41 AM   #8
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When I've dropped slab areas for Saltillo, Davy, it's usually a 1 1/2" drop, rather than the 3 1/2" like Phil has. And I'd mud and tile the room before installing the base cabinets and such, unlike what we see in his photos. Have you seen rooms done like that?
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Unread 10-06-2022, 08:27 AM   #9
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I am guessing they figured they could save a couple of bags of mortar mix by not filling those areas.
I will be back later with more questions. Was not expecting to be using a mortar bed for the entire room.
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Unread 10-06-2022, 05:02 PM   #10
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I agree, Kelly. The drop was usually 1 1/2 inches.
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Unread 10-11-2022, 06:24 PM   #11
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Just when I thought I knew what I was doing I discover that my son's bathroom is going to need a mortar bed over the entire floor and I have never done a mortar bed so I have lots of questions. Bathroom is roughly 6ft x 8ft with a shower along the right wall so there will be a 6ft curb. I will be there for a week in late Oct to help get the project started.
1 Would order of operation be tile shower walls (minus bottom row), install curb, mortar bed shower floor then mortar bed bathroom floor?
2 The concrete slab will not be flat or level. How do we install the curb, we will be using a foam curb? Do we build a small mortar bed under the curb to create a level surface?
3 After installing the mortar bed for the shower how long do we have to wait before we can install the membrane and then tile?
Thanks so much
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Unread 10-11-2022, 07:30 PM   #12
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1. You could do that, I suppose, but then you'd be walking over your new mud floor while finishing your shower. I'd likely do the shower and then place the mortar for the bathroom floor and tile it.

But if you wanna do all your mud work at one go, you'll just need to let that bathroom floor cure for at least a day and then protect it with some plywood or similar.

2. You mean one of those too-big and not properly sloped foam things? They're usually bonded to the floor with thinset mortar. With some of the non-sag mortars, you could have thicknesses of half an inch or more. How far out of level and flat is this concrete floor in that area?

3. Technically, you don't need to wait at all. But unless you've developed your troweling skills to a fine edge, and you can reach all parts of the shower floor without getting on it at all, I'd recommend you cover it with polyethylene sheeting and let it cure for at least a day. Any mistakes in your troweling over a fresh mortar bed or in applying your membrane, and you'll know immediately whether that was a good idea for you. It is not a good eye-dee for me, I assure you.

The tile industry says 20 hours is the minimum cure time for a "cured mortar bed," but longer cure times are recommended. You'll want that surface to be free of loose sand and debris before trying to trowel on thinset mortar and apply that sheet membrane.

My opinion; worth price charged.
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Unread 10-14-2022, 10:26 AM   #13
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Maybe a change in design. Does "whatever she says" still apply when it is your daughter-in-law
She wants a curbless shower. When demo is done we will have concrete slab that is at least 2in lower than the bedroom slab.
1 How would you do the mortar bed when there are two sections, the sloped shower area and the rest of the bathroom floor? Can they be done days apart?
2 The main floor will be 5ft x 6ft. In the videos I see them set screed sticks on walls of mortar and set those to be level to screed off of. As beginners I could see this taking us a while to do and end up with a mortar bed that is drying out. Are there any suggestions on how screed sticks could be set up ahead of time like using a 1x4 cut to about 2in wide and set on edge on the concrete floor and somehow shimmed to be level?
3 Once we pour the mortar mix out, about how much time do we have to work with it?
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Unread 10-14-2022, 04:27 PM   #14
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Quote:
Originally Posted by Phil
Maybe a change in design. Does "whatever she says" still apply when it is your daughter-in-law
Well, I think you might better axe your son about that one, Phil.

1. Yes. You'll almost certainly want to have a movement accommodation joint where the floor meets the shower and a cold joint in the mortar there would be fine.

2. Two of you can easily mud a 5x6-foot area. If you want to use some sort of screed sticks along the perimeter, that's fine, too. We'd normally put some SilSeal or similar foam around the perimeter before placing the mortar and just hard-pack a mortar screed a few inches wide to work from. But putting some 1x wood strips around the perimeter would be OK, too. When you finish, you'd wanna remove the strips, put some foam down in the groove and fill it with mortar. You'll find the narrow strips won't be terribly helpful while actually screeding the floor flat as your necessary back-and-forth motion of your screed won't allow you to stay on the wood strips. The wood strips can be helpful in repairing and re-packing your mortar screed strips, though. And don't forget that you need to firmly pack your mortar before shaping. No need to beat it into submission, but smack it smartly with a wood float or piece of 2x material

You're planning a bonded mortar bed or reinforced mortar bed?

3. You'll have 30 to 45 minutes open time to work that mud, and with two of you to mix and place, you should be able to handle that. Pre-mixing dry material in buckets and having them staged in the work area can make it even easier. Doing that with a Bucket Mortar Mixer and a pre-measured water container makes it even easier. How many buckets would be determined by how thick you intend to make this mortar bed.

My opinion; worth price charged.
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Unread 10-14-2022, 06:18 PM   #15
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Thanks that was very helpful. Can you explain what a movement accommodation joint is? Do we need to put something between the two mortar beds.
Thanks
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