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Unread 06-26-2020, 10:03 AM   #16
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Nick, you can use the 1x4 boards in that application but they're a bit narrow for my liking and more prone to splitting. I favor rips of 3/4" plywood five or so inches wide for the application. Glue and screw from the top half of the strip under the edge of the installed panel, then glue and screw from the top the next panel when installed. Even with your 1x4s and a little splitting you'll have more support than any factory T&G edge.

Be sure to cut your strips shorter than the between-joist span so they don't touch the joist on either end.

My opinion; worth price charged.
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Unread 06-26-2020, 10:24 AM   #17
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Thanks CX. And since I'm stubborn (not going with SOG as you'd prefer) does that BCX plywood I linked look ok?

I'll use the plywood strips as you suggested, btw.
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Unread 06-26-2020, 11:18 AM   #18
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Look for an actual grade stamp on the panels, but that is probably an exterior glue BC grade plywood and would be a good choice for your subfloor.

(There is, to my knowledge, no BCX grade of plywood)

My opinion; worth price charged.
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Unread 06-27-2020, 06:09 AM   #19
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Be mindful of your screw lengths also, Nick. With "construction" screws, even deck screws, the longer the screw is the longer the smooth portion of the shank is. For fastening those plywood strips you don't want much of the smooth portion of the shank of the screw extending into the strip. Since the strips will be backed up with glue (I'd use wood glue, fully spread, not construction adhesive) I'd think 1.5" screws will work fine. For the plywood to joists use construction adhesive and 2" screws.
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Unread 06-27-2020, 05:10 PM   #20
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Thanks CX and Dan. I find this forum amazing--I log on to ask a question and somehow the answer is there waiting for me!

But a couple of additional subfloor fastener questions:
1. Is typical screw spacing ok (6" on edges/12" in the field), even though I'm just laying ditra and then tile over the 3/4" ply?

2. What exact type of 1 1/2" and 2" screws should I use for fastening the plywood (i.e., do I need to worry about alkali resistance, special threads?)

3. Is there a good size/brand of construction screw to use for blocking joists?

Thanks!
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Unread 06-28-2020, 06:43 AM   #21
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Nick, I'd probably tighten up that fastener spacing a bit; 8 ish inches in the field, 4 to 5 at the seams. I like to off-set the fasteners at the seams so that no two are directly across from each other.

No need to worry about alkali resistance or special threads. I used Grip Rite screws, labeled as "construction", from Depot. They work well and come with a star drive bit in each box. You could use similar screws for treated lumber but those are over kill.

Drive them so that the heads are juuuust below the surface of the plywood. Watch out for screw jacking.
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Unread 07-12-2020, 09:20 PM   #22
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Some of my joists have a slope!

Hello I'm wondering if anyone has any guidance on how to address my joist situation. I was so focused on sistering that I've just now realized that about one half of the room has about a 1/8" per ft slope at the tops of the joists. I'm attaching a sketch here showing the cross section view of the joists.

Essentially there are two adjacent ~6 foot wide sections of the room that are both essentially flat. One is level, and one has a slope to it.

I'm inclined to proceed with my plan to use small format ceramic tile, since both halves of the room are flat. But I thought I'd check with you all here if there was something I'm missing. If I tried to flatten the joists across the entire room, I'd end up having to take off a good 3/4" from the tops of the joists on the side of the room opposite from where the slope is.

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Unread 07-12-2020, 09:54 PM   #23
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Nick, I'd first wanna know why the situation exists. Does this appear to be something intentionally done? Or has one part of this floor settled that much for some reason?

Can't tell what part of the floor was being sistered, but you could bring all the low joist tops into plane with some sistering. Never a good idea to cut down the joists. And the sistering for this purpose could just be some 2x6 material where you don't need the structural addition, just the leveling.

My opinion; worth price charged.
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Unread 07-13-2020, 12:27 PM   #24
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Yeah, I can't figure out an explanation for it, CX. Does not seem intentional. The vanity and entrance to the bathroom make up this sloped section-maybe the heavy traffic sunk it over 40 years???
I can't find another part of the house that is not level, not directly below on the first floor or next to it on the second floor.

So you'd recommend 2x6's sistered to bring it flat/level with the rest of the room?
They will be about 3/4" proud of the existing joists at the lowest point at the far edge of the room-is that okay?

And you're definitely saying that I couldn't make it work as is? By making sure I had a tile seam at that point where the two flat sections meet, I thought I would be okay...

Also, can I change the name of the thread to something more generic like "Nick's Master Bath"?

Thanks
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Unread 07-13-2020, 03:33 PM   #25
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Quote:
Originally Posted by Nick
And you're definitely saying that I couldn't make it work as is?
I am absolutely not saying that, Nick. I'm only suggesting a way to level the floor if you want it level.

Your tiles don't give a rat's patooti whether the floor is level, they care only about flat. If you have two flat planes and you think you can effectively make an acceptable plane change in your tile installation at the junction, I see no technical reason you shouldn't do that.

My opinio; worth price charged.
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Unread 07-19-2020, 04:14 PM   #26
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I forgot to ask, would you address the change in plane with the subfloor in some way?

I was planning on offsetting the 3/4" sheets of plywood as I fastened them down and the nearest seam on the short sides of the plywood would be ~3 feet away from the change in plane.
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Unread 11-16-2020, 01:04 PM   #27
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Flattening with sistered joists, floor under wall?

I decided I will go ahead and sister the rest of the joists with 2x6's to flatten the floor instead of trying to rely on SLC. I have as much as 3/8" of sag on a couple of joists. A couple of questions on it:

-I used kiln dried DF on the sistering to this point, but is that overkill? Or is green lumber not advisable for sistering?

-I know this has probably been covered somewhere, but I couldn't find it by searching the forum. When fixing joists/subfloor, how do you handle a partition wall that is parallel to, but in between joists (picture below)? The joist adjacent to the wall has about a 1/4" of sag that I'd like to address with a sister, but I'm wondering how to address that last section of subfloor between the original sagging joist and the wall. I can't have the wall floating on plywood that doesn't span joist to joist, but then I'll be left with a ~6" section of subfloor next to the wall that will not be flush with the rest of the room (after it's been raised/flattened by my sistering). This must be a fairly common situation, that I'm guessing you pros have devised a clever workaround for. Any suggestions?

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Unread 11-16-2020, 06:32 PM   #28
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There is no need to use any particularly stiff wood species for sistering if the only function of the sister is to bring the joist tops into plane. I don't know what you might mean by "green" lumber. You're talking about lumber that is fresh from the mill before any drying? If so, I'd advise against that. But any kiln dried lumber should suffice.

The problem at your wall is indeed common and yours is a bad case because your joist is pretty far from the wall. If you have access to the wall area from below, you can install some cross blocking to support the wall if that's not already been done in the initial framing. If you don't have access from below, make some.

If you're not willing to do that (you really should), you've made the situation a bit worse by cutting the existing subflooring in the center of the joist, giving you no really good way to attach that subflooring. Cutting out the subfloor such that the wall is no longer sitting on subflooring that spans at least three joists has substantially weakened the wall support (unless cross-blocking was installed) and lack of ability to fasten what's left makes it worse.

About all you can do from the top is to fill the void that will be left between new subflooring and wall before you install your tile substrate and hope for the best.

My opinion; worth price charged.
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Unread 11-17-2020, 10:44 AM   #29
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Thanks CX. I appreciate your wisdom, as always. That wall is sitting on subfloor that spans 3 or more joists (including some on the other side of the wall), so I think I will be ok. Also, I cut that floor out almost 6 months ago now, and the wall hasn't shifted. I understand it's not optimal but I'm comfortable with it.

Currently the joists are not flat, or level. They are all higher on the exterior side of the room and slope down about 3/8" as they travel ~11' to center beam of the house. Therefore when I need to raise up that small section next to the wall, I see 2 options:

1. Level and flatten the room with my sistering, and then use SLC in that small section by the wall.

2. Only flatten the room with my sistering, and then use some other approach besides SLC to fill that void next to the wall. (Was thinking I could spread a flexible floor patch compound in there, but I'd love any specific suggestion for such an approach). I was hoping this would be possible because I am trying to avoid a tall transition at the threshold that is likely if I level the room with the sistering. But I'm afraid that it might be a tough task to get the subfloor flat enough with my sistering alone, and should maybe just plan on SLC with option 1.

I'd greatly appreciate your thoughts on these options, or anything I'm missing.

In general, I'm really curious if you think it's reasonable to expect my sistering to provide a flat enough surface to meet TCNA standards for large (or even small) format tile. Or, from your experience, just considering standard variation in joist/plywood materials, is SLC most likely going to required?
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Unread 11-17-2020, 04:26 PM   #30
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That wall would make me a bit nervous too, Nick, with it bearing on the plywood that has only 3/4" of edge support on that one joist. But it's yours, so....

Yes, you can create a level and flat floor with those sisters, I did so on my MBR floor which measured roughly 14X7. But unless you actually need to add strength to the existing joists I recommend that you use 2X4's or even 2X3's instead. They will be bendy enough to allow you to push/pull them to the height you want.

When I did mine I basically built frames that would fit snuggly between a pair of joists. Being snug they would stay in place and I could tap them here, lift them there, to get them level before committing screws to them. Once I had them where I wanted I clamped them in place and took extra care to run my screws in straight. Building them as boxes allowed me to securely attach the ends with screws so that the end of the plywood would have support.

Even after all that work I still need to do a little shimming here and there, I used drywall shims. Mine was a little different because I was recessing the 1st layer of ply between the joists.
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