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Unread 02-17-2019, 10:36 PM   #46
cx
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Quote:
Originally Posted by Renee
We all know this contractor is not capable to achieve leveling by dry pack mud
Your floor needn't be level, Renee, but it needs to be flat. If he can't do it using mud, you can learn to do it yourself in a room that small. If not on your first try, likely on your second.

If your contractor can't make a flat floor that size for you using deck mud, I'm not real confident he can do it using a self-leveling compound. You might wanna start practicing with some deck mud on your own.
Quote:
Originally Posted by Renee
...material is ACX EXTERIOR grade 23/32” thick...
Let's get your terminology straightened up here. The grade of that plywood is AC. If it says Exterior on the grade stamp, that is the exposure rating. You want either Exterior, EXT, or Exposure 1 as your exposure rating. The 23/32nds" thickness makes it nominal 3/4" plywood. What you describe is fine for your first layer of subflooring.

But with your joist spacing, you'll need a second layer for a ceramic tile installation. The second layer must also be exterior glue plywood with no face of grade lower than C, but can be square-edge rather than T&G.

You'll also want to evaluate your joist structure and we can't help with that without knowing the species, grade, and unsupported span of the joists. You can enter your information into the Deflectometer in the dark blue bar near the top of the page to get an initial go/no go rating.

If you are removing all your subflooring, you should be able to bring your joist tops into plane such that you don't need self-leveling products at all.

If you plan to use a CBU as your tiling substrate, you must install that first if you plan also to use a self-leveling material.

My opinion; worth price charged.
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Unread 02-17-2019, 11:08 PM   #47
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Hi CX, thank you.

Current tiny powder room is flat now with leveling, when I asked him about usage of primer prior to self leveling, he swore that he used it, so even tough the floor is not level, the surface itself is now flat,then instead of taking out whole thing( though there is absence of roof felt, he put metal lath and thick concrete(dampy, so not technically dry pack mud), primer and self leveling is what current floor is at, I can and will ask him to leave a gap between floor and the wall 1/8”-1/4”. Is this okay? I think some of joist are not level( slight 1/4”) so even we take out whole thing, I feel like still need some SLC IF I WANT THE PERFECT LEVELING but I’m starting to comprise that this floor is flat enough to put tile over. if you think my contractor is not competent enough to achieve perfectly level floor with existing subfloor and 1/2” plywood on top with SLC then mind as well leaving things where it is, you migh wonder why I’m sticking with him.. well 1. Cost to hire new contractor who will charge a lot for demo 2. Hate to send him home paying for just demo portion. ( my conscience will pressure me to pay him twice much then it’s almost cost of complete installation.

I calculated and this is what I got
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Unread 02-17-2019, 11:14 PM   #48
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Self leveler usually needs a minimum thickness. It’s not meant to have a feather edge. So you typically can’t use it in just one spot, it needs to be a pour over the entire area with the thickness over the highest spot in the substrate equal to or greater than the manufacturer’s min thickness.

You can’t install cement board over a self leveler, the fasteners used to install the board would crack the leveler.
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Unread 02-17-2019, 11:14 PM   #49
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I missed plane the joist suggestion part, though it’s a very good suggestion, hoping to get some feedback if my alternate plan is okay as well. To sum up, keep the existing work, leave a gap by wall and tile over, of course I’m leaning toward this route but if any of pro doesn’t like the sound of it, willing to re-do. Thank you

Lou, noted, thank you, totally make sense!
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Unread 02-17-2019, 11:54 PM   #50
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If you're using cbu, you do not want to install SLC first...the fasteners you use to anchor the cbu tend to crack up slc. If it is needed, install it after the cbu is installed.

Some slc can be installed over ply even without a primer (Ardex's LiquidBackerBoard is one), but the vast majority want both a primer AND, over a wooden subfloor, a thicker layer. LiquidBackerBoard is an exception to that general rule.
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Unread 02-18-2019, 12:30 AM   #51
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Jim, noted with thanks!

I tend to babble, so let me try to be more precise.

Current situation:
1. 23/32” thick AC grade exterior plywood
2. No roofing felt
3. Metal lath
4. Dampy concrete( completely dried following morning)
5. Primer
6. SLC
7. No gap FLOOR TO THE WALL-will make 1/8-1/4 gap for contraction and expansion
8. Floor is not level but flat
9. Will do two coats of redguard
10. Thinset and grout

If the current situation doe not sound good,
1. Demo dampy concrete
2. Check plywood is well screwed into joist( the grain is sits on perpendicular, witnessed that)
3. Add AC grade exterior 1/2” plywood( staggered to plywood underneath, do not fastened to the joist for movement) Edit-upon CX’s direction, deleted glueing part
4. Attach 1/4” cement board with thinset, put alkali tape on seams
5. If desired, pour SLC(prime first), All over, but if after cement board looks flat but not level by 1/4”, then option of omitting is possible
6. Two coats of red guard
6. Set tile with thinset
7. Grout


Prefer keeping the current floor but willing to redo, if it’s redo situation, please coonfirm that I have all the steps?

One more question, would it be more preferable if full plywood is used instead of seam? My powder room is so small, I know one 4x8 sheet can cover( currently my installer put seams on center of the room( toilet flange is located in center by back side of the wall)thank you!
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Unread 02-18-2019, 08:55 AM   #52
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Renee, Now that we know your joist spacing, your single layer subfloor does not even qualify for a properly executed mortar bed. Entirely up to you, of course, whether you want to tile over what you have.
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Unread 02-18-2019, 09:24 AM   #53
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Question

CX, this is what I want to hear to push myself for re-do, thanks CX, will redo with cement board
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Unread 02-18-2019, 09:29 AM   #54
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Eliminate the part where you try to glue the second layer of subflooring. Mechanical fasteners only.

My opinion; worth price charged.
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Unread 02-18-2019, 09:35 AM   #55
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Thank you!
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Unread 03-03-2019, 02:02 PM   #56
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Hi everyone,

Little bit of update here, so the tiler left the job halfway doing demo the mortar bed on the first day he came back, I just had to recover from whole ordeal and wanted to completely mortar bed to be out before I come back here asking advices. I’m so glad that I took everyone’s advices from here, i found out why one powder room floor after mortar bed was so high, the tile installer cut plywood around toilet flange too big, he took out plaster wall(!) to take some 1/4” thick wood lath to put around toilet flange so that screws will have some area to mount on, you would think he would take some cues from the first powder room to work on the second, but astonishingly, same story but this time he filled the 1 1/4” gap with spray foam around the flange,




With all mortar bed being demoed, here are some pictures of joist conditions.
2x6 around cast iron waste pipe is cut so deeply I’m surprised it lasted this long, my question,

Since there is no room to sister the joist, I’m hoping I can add 2x6 in the center of 24” O.C joist (instead of sister right next to the joist due to lack of space), is this okay practice to strengthen the joist?

Any advice from the pictures below would be appreciated,
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