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Unread 10-07-2019, 09:53 AM   #31
cx
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I think not so bad, Jesse. Without actually seeing the situation it's difficult to say for sure, but if I had the option of installing two layers of nominal 3/4" plywood subflooring and had to cantilever 6" of it past a perimeter joist, I think I'd still be comfortable tiling over it. Unless there's significant foot traffic in that area, which I think unlikely, I don't think it will be a problem. I have no data with which to back that up, but I'd even be inclined to do that in a customer's house were the situation to arise. My warranty information is below.

My opinion; worth price charged.
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Unread 10-07-2019, 10:16 AM   #32
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I’m not sure I follow you. Just to be clear.
The joists in the field of this room are 18” away from the parallel perimeter wall leaving the next joist 6” past the walls. So I’d be cantilevered approx 18” of new sub floor , granted if I leave the 1/2” under it won’t technically be cantilevered.
Hope This makes sense.
Are you saying I should be fine you’d be ok leaving the existing plywood and doubling up plywood over it?
Me and my guy are literally standing around and are about to pull the trigger on this. Lol
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Unread 10-07-2019, 11:19 AM   #33
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Well, gut instincts is telling me to rip out the plywood, block , and start fresh.
Thanks Cx for taking the time to help me out .
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Unread 10-07-2019, 11:55 AM   #34
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Clearly I misunderstood the situation. Yes, if your cantilever is actually 18 inches, Jesse, I would agree that new support of some kind under the subflooring at those edges would be necessary.


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Unread 10-07-2019, 12:14 PM   #35
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Sorry I wasn’t as clear as I should of been.
I am going to use 4x4 hangers under the obstructed floor for ease of installation to tie in a double stack of 2x4 on to the top chord. And simply toe screw the accessible side of the block to the adjacent joist. Looks do-able.
Thanks again.
I’m sure I’ll be back with more questions.
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Unread 10-08-2019, 11:41 PM   #36
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Ok so, blocks are in and spaced out 16” o.c. Between joists that are 24” o.c. .
The original height of the floor was 2” (1.5” concrete and .5” plywood)
And I was thinking of not including the 1/2” plywood for the height and just doubling up 23/32 bcx , putting in some ditra , with the mortar and tile making up the difference for an almost flush transition.
I just received a 2018 TCNA handbook and also 2017/2018 TCNA Reference manual and have a few questions I would like clarity on.
In the reference manual in chapter 2 / substrates , it’s talking about Interior Horizontal installation of tile over Exterior Glue Plywood (EGP) .. it does reference f-142 & f-143 which do not exactly apply to my criteria but, still confuses me (which some may argue that it’s easy to do) . So , on line #5 it states “plywood (which I presume it’s talking about the subfloor) must be securely fastened to the floor joist with 4d ring shank nails spaced 6” o.c. Yada yada yada..Underlayment plywood SHOULD NOT be glued to subfloor.”
So the question is, WHY not?

Now in the handbook sec F147 for joist max. 24” o.c. / plywood sub /plywood underpayment/ uncoupling membrane it states;
“Subfloor- min 23/32 tongue and groove.”
1. Would it make a difference if I use straight edge bcx? I mean considering it’s blocked heavily ?
2. If I do use 23/32 bcx for subfloor , should I glue (PL adhesive) and ring shank nail it or screw it to the joist and blocks?
3. The 23/32 bcx underlayment, should I glue (titebond) and screw avoiding joist and blocking?
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Unread 10-09-2019, 12:07 AM   #37
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The reason for no glue between subfloor and underlayment is that unless it's a full spread of glue, meaning it covers the entire sheet evenly, it will potentially create voids between areas of glue. Those voids allow for vertical movement, which a tile installation can't survive.

1. If you use straight edge panels, then every seam that runs perpendicular to the joists must have blocking to join the panels. There are several ways to do that, but that's the general idea.

2. I prefer deck screws for most every application. They hold better without backing out, but if you do need to remove one or more for whatever reason, you can do so easily, and reuse them. Not so with ring shank nails.

Definitely use glue between the joists and subfloor.

3. Again, no glue between subfloor and underlayment. You could use 1 1/2" or even 1 5/8" screws and not worry about the joists. If you use screws longer than that, you'll have to intentionally avoid the joists and blocking.
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Unread 10-09-2019, 12:38 AM   #38
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Hi Kevin.
Thanks for replying.
That makes sense . I just thought it meant no glue of any kind.
1. Regarding the straight edge plywood, that also makes sense. I better make sure my 16” o.c. blocking will actually coincide with the joints. Thanks for pointing that out.
2. Yes I usually exclusively use torq head decking screws but, after reading this article it made me think if there was a technical reason that I didn’t know of for the slightly less fastening power of ring shank nails. The way i see it is (and I’m sure I’m wrong but, learning) that if I’m glueing the subfloor and mechanically fastening it then if there is still a need for spacing between plywood butt joints for expansion and contraction then maybe there is a possibility for subfloor assembly movement isolation from the joist via nail movement. Lol
3. So a full spread of wood glue?
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Last edited by Yes si; 10-09-2019 at 12:45 AM. Reason: Misspelling correction
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Unread 10-09-2019, 12:52 AM   #39
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Yes, you'll need a small-notched trowel, I don't know that there is actually a recommendation for what size.

Something like a 1/8" square notch, or a 3/16" v-notch. Just make sure you cover the entire board quickly, and cover it quickly. You'll probably want to pre-drill the screws beforehand so you can get it cinched down before the glue starts to dry.

A helper would be a good thing to have for that job. But at the minimum, have two drills on hand. One for drilling and one for driving screws.
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Unread 10-09-2019, 01:19 AM   #40
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Sounds like a plan. I thank you sir. I better get a few hours of sleep to bang this out in the morning. Have a good night.
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Unread 10-22-2019, 09:14 PM   #41
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Quartz floating corner bench advice needed

So, I ended up cutting out the old subfloor, installed an excessive amount of blocking. Glued and screwed 23/32 bcx to joist and blocking, laminated on another layer of 23/32 bcx and screwed in the appropriate pattern with 1 5/8 decking screws.
Now I’m working with a 3x5 tub to shower conversion.
I’ll be using Kerdi over drywall . 2 sides are type x fire rated drywall because it’s at a common wall of a condo . I have blocking in the corner for a traditional bolt on corner bench but I read here that I can slot the tile to use the actual tile to suspend the bench.
What I have is scrap pieces 2cm quartz that I am planning shaping and polishing to use for the corner bench, curb top, and floor transition.
4x9” ceramic tiles will be used.
** My question is , will I have a problem with the shear strength of the tile, tile to Kerdi adhesion?
Will the drywall hold up in this application?
The long side framing is 16” o.c. With 5/8” type x drywall & the other wall has a stud every 7.5” this wall has 1/2” drywall (extra studs for niche framing) plus the blocking of coarse.
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