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Unread 09-12-2019, 09:35 AM   #1
tile_n00b
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Expand mud bed for bathroom floor or rip it out?

I've got an ~7' x 6' tile bathroom floor I'm planning to redo as part of a whole bathroom remodel, and have hit a bit of a snag after demolition.

The existing floor is two layers of tile over a mud bed bonded to the 3/4" plywood subfloor with metal lath. The previous owners put 12" x 12" ceramic tile over the original 1987 install of 4" x 4" tiles. My original plan was to remove both layers of tile, and reuse the existing mud bed for new 12" x 12" porcelain tile. I am not changing the layout of the bathroom. However, the original mud bud does not extend under the location of the original vanity cabinet. I am replacing the vanity, and the new one does not exactly match the footprint of the old one. I was expecting to tile all the way to the wall and put the new vanity on top of the tile, but now I'm not sure how to proceed.

The existing non-original vanity was installed by the previous owners. They laid some 2x4's in the open area of subfloor and tiled over them to support the vanity. I removed the 2x4's and don't plan on using that approach for fear of the tiles cracking.

I've considered these options:
  • Rip out the mud bed and use Ditra. I did this in my master bath, but it's a lot of work because my joists are 24" o.c., requiring the install of an extra layer of plywood over the subfloor.
  • Expand the existing mud bed under the vanity area and tile over it. My thought here was I could demolish a few inches of the existing mud bed, overlap new metal lath with the old, and bond the new mud bed section to the old with thinset.
  • A third more creative option?

This section of floor will be mostly covered by the new vanity, but not entirely. If the tile cracks at the edge of the old mud bed, it will be visible right in front of the vanity.

Here's a picture of the area. I can take some better/closer photos and upload later today.
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Unread 09-12-2019, 09:58 AM   #2
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Ryan,

It seems to me that removing the existing mud bed (you'll be removing both layers of tile in either case) and covering the whole floor with a new layer of 3/4" ply would be about as much work are trying to reliably tie a new mud bed into the told one, which may - or may not, work.

Easy choice for me, and I'd sleep better without worrying about that cold joint, but I ain't the one doing the work. You'd also get a better look at the subfloor to check for any issues, and be able to secure it to the joists with screws if it isn't already.
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Unread 09-12-2019, 12:08 PM   #3
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Mud it

Chances are the original installer chose mud bed because floor had up and down and was off level. That original floor the subfloor , is still there is still R&R so mud it with tar paper and wire and deck mud. simple

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Unread 09-12-2019, 05:02 PM   #4
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Easy decision, I'd bust it all out and mud the whole floor. It's only 6x7.
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Unread 09-13-2019, 10:12 AM   #5
tile_n00b
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Thanks for all the input so far.

I guess I could re-mud the whole floor...

Is there a typical thickness I need the mud bed to be for 12" x 12" porcelain tile with a subfloor that's 3/4" T&G plywood on TJI joists 24" o.c.? The joist span under the bathroom is only about 8 feet.

My main concern there was getting the mud bed nice and flat/level on top so that the tile install doesn't look crappy. The only mud work I've done is a 4' x 5' shower pan in my master bathroom.
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Unread 09-13-2019, 10:19 AM   #6
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you can use a screed that goes wall to wall, like a straight 2x6 or something.

put a level on it or even screw level strips on the walls as a guide.
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Unread 09-13-2019, 10:46 AM   #7
ss3964spd
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Unless the floor is way not flat, and or way not level, I'd throw down a couple sheets of 3/4" and be done with it. Admittedly though, my opinion is based on having effectively zero experience doing a quality mud job.
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Unread 09-13-2019, 05:47 PM   #8
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So you got some mud experience, Great you are ahead of the game. Minimum thickness of a unbonded mud bed is 1 1/4 in. And you can do as mike suggested and nail up perimeter screeds and screed off of them or you can set your perimeter height then tap in some screed sticks either way works, just depends on the layout of your bathroom. The benefits of mudding is that this a one and done ready to tile floor that is as flat as you can get. If I could set tile over mud every day I would be in hog heaven.
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Unread 09-13-2019, 06:30 PM   #9
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Run mud screeds around the perimeter and fill in the middle.
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Unread 10-07-2019, 03:33 PM   #10
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Thanks everyone for the advice!

I finally got around to pulling up the two layers of old tile this weekend with an air hammer. The top layer put down by the previous homeowners was attached with mastic, and a real pain to remove. The original tiles below were put down with thinset and mostly popped off nicely. Unfortunately the original mud bed was pretty thin in a few areas and started crumbling when I pulled up the tiles. So I decided to just rip the whole thing out down to the plywood.

I'm thinking I'll end up putting down a layer of 1/2" ply and Ditra. The reduced height will help with the transition to carpet in the hallway, and I'm familiar with the process. I found doing Ditra for my other bathroom floor was easier than working with the deck mud in my shower pan. Plus the cost isn't much greater since it's a small bathroom.
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Unread 11-25-2019, 05:34 PM   #11
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A new challenger approaches: uneven subfloor!

The subfloor dips down about 1/4" and back up across 4' from the wall to the center of the bathroom (along the length of the level in the photos). So a slope of about 1/8" per foot. The rest of the floor is flat to the other wall. I think SLC is out of the question because the floor is also out of level overall, with the wall the level is touching being the high side. I don't want to raise the height of the floor on the opposite side of the bathroom where the door is any more than necessary. I've already bought the 1/2" plywood and Ditra, so I'd like to proceed with that if there's a viable option to level out this section.

1. Could I screed thinset a bit thicker in this area over the ditra so the tiles are flat?
2. If not, is there another option besides going to a mud bed?

Also I need to correct something in a previous post. The joists are 19.2" O.C. in this part of the house. So the subfloor is 3/4" T&G Plywood over 19.2" O.C. TJI's with a short 8 foot span. The joists run perpendicular to the level in the photos. From the Ditra manual, I no longer need the 1/2" plywood over the existing subfloor.
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Unread 11-25-2019, 06:13 PM   #12
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If you're not going to install the second sheet of ply, and are going to install the Ditra on it directly (it's still a good idea, as the old stuff may not be as good as it would be if it were new), you might be able to use something like Ardex LiquidBackerboard. Unlike most SLC, it can go down without a primer and feather to zero over wood. I'm not sure it will work, but it is easily moved around. Some SLCs are thixotropic, which means that they don't actually self-level - they move when you move them, but stay when you stop. If you choose to use that second sheet of ply, apply that above. If you try to do that then install the second layer, the screws can cause the material to crack off. Thinset will stick to it fine, though.
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Unread 11-25-2019, 06:39 PM   #13
tile_n00b
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Thanks for the info!

I'm definitely in favor of still installing the 1/2" plywood. I already have it on hand and would prefer to have the floor as stiff as possible. I did a quick search on the Ardex LiquidBackerboard and came across their TL Patch Tile Leveler which can be applied to wood subfloors without lath, and be between 1" and feather thin. This would be easier to work with than the liquid since the whole floor will still be out of level, and I only care about making it flat. Could I just skim that across the 1/2" ply in the low area and let it dry, then apply the Ditra on top?

Ardex TL Patch: https://www.elleganthomedesign.com/a...h-tile-leveler
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Unread 11-25-2019, 06:45 PM   #14
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Quote:
Originally Posted by jadnashua
it can go down without a primer and feather to zero over wood
From the data sheet


Wood subfloors require priming with ARDEX P 51 at full
strength (do not dilute). Thickness of Installation
Install at a minimum thickness of 1/8’’ (3 mm) over the
highest point in the floor, which typically results in an average
thickness of 1/4’’ (6 mm) or more over the entire floor.
ARDEX Liquid BackerBoard can be installed up to 1 1/4”
(3.1 cm) thick.
To match existing elevations, ARDEX Liquid BackerBoard
can be tapered to as thin an application as the sand in the
material will allow. If a true featheredge is needed, ARDEX
recommends using ARDEX TL PATCH for transitions.


https://cdn.ardexamericas.com/wp-con...nical-Data.pdf

I am a big fan of ardex,it is my go to for thinset, patch and self leveler they have a bundle of different self levelers


https://www.ardexamericas.com/produc...self-leveling/
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Unread 11-25-2019, 06:46 PM   #15
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Ryan, with a small wood framed floor that needs to be flattened and could stand to be leveled as well, I wouldn't even consider any option other than a mud bed if I had the vertical room for it, which you apparently do. One of the best features of such mud beds is the ability to go from what you have to a level and near perfectly flat substrate for your tile installation.

You could try to level and flatten your tile installation while setting the tiles, but I think you'll rather quickly discover why we don't recommend you try that.

If you do other than the mud bed, I'd strongly recommend the second layer of plywood subflooring, despite Schluter's advertised minimum for their Ditra.

My opinion; worth price charged.
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