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Unread 05-21-2020, 08:02 PM   #16
Kman
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How many square feet will be tiled?
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Unread 05-21-2020, 08:51 PM   #17
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Kman,

About 175 ft^2

Jim,
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Unread 05-21-2020, 09:15 PM   #18
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I would go with a floor sander unless you just have a small area to sand down. Working that floor down with a belt sander will wear you down very quickly.

I'll also echo Jim's suggestions about sinking the nail and screw heads before you start.
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Unread 05-22-2020, 08:48 PM   #19
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I think I had a different idea of sanding when I was talking about
sanding the high spots. I was thinking of just sanding the high spots
mostly caused by the cupping in the planks, maybe 1/16 max.
The floor dips down about 3/8", that would be a LOT of sanding to
take 3/8" off most of the floor.
I was thinking of filling in the low spots with shim material, then
putting the plywood down. Or just putting the plywood down and
then filling in the low spots on top of the plywood with a motor
based leveler. I am guessing that either of these ways would work.

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Unread 05-22-2020, 10:41 PM   #20
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If you're taking off just 1/16", a belt sander would work. I imagine you're just hitting the joints, not the center of the boards.

I wouldn't use shims. Just secure the plywood with screws and use a leveling compound on the plywood if using a tile membrane, or on the cement board if that's your choice of tiling substrate.
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Unread 05-23-2020, 11:27 AM   #21
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If you follow the fastener spacing recommended, that will generally pull the plywood down to the surface beneath, so if it isn't flat, that will follow. If things are way off, a thicker ply may work out better as there are limits. You're trying to do two things: isolate the solid lumber from the tile, and help add strength. You don't want a point load to be an issue if it's not supported underneath unless it's strong enough on its own to enable tiling.

If the planks are cupped, they may split or bend back once you add the screws...see what it looks like once you've refastened everything before adding the new ply.
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Unread 05-25-2020, 11:13 PM   #22
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I am starting to figure out what I need/want to do with
my floor. After more research and influence from Sal DiBlasi's videos,
I am going with a decoupling membrane, probably Ditra.
And not going the cement board route.

Now back to the plywood, I got several questions, and searching
the internet I feel I got information overload and sometimes it
is hard to tell what is the most correct thing to do. It seems that
there is really convincing information and videos that have less then
a 10% change of lasting more than a year. Then there is a lot of
information and videos that have around 80% chance of lasting,
but with many variables. I have a hard time finding that information
that has a 99% chance of lasting for years to come.

Anyway, should I post me plywood questions here, or start a new thread?

Thanks,
Jim
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Unread 05-25-2020, 11:18 PM   #23
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Please keep all the project questions on this thread, Jim.
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Unread 05-26-2020, 09:25 PM   #24
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The current plane is this
1. put 1/2" plywood over the plank subfloor.
2. flatten the floor with a cement based leveler.
3. apply a decoupling membrane(eg. Dirta).
4. Apply tile.

1. Since I am covering most of the plywood with
a leveler and then a decoupling membrane.
Will CDX 4 ply 1/2" be ok? Or do I really need BCX?

2. No adhesive between plank subfloor and plywood?

3. Space between sheet, I read nothing, 1/32, 1/16, 1/8,
what should the space between plywood sheets be?

4. Perimeter spacing, how much if any space should be left
between the plywood and walls?

5. Put the seam over the joist, or make sure the seam between
plywood sheets is off the joist a few inches?

Thanks for any help.
Jim
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Unread 05-26-2020, 09:49 PM   #25
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1. No, you do not want to use any ply with a D-face...that means it can have voids...you don't want any weak points.
2. No adhesive, but lots of screws not into the joists.
3. In a subfloor, spacing is needed as the building is likely open to the weather. Some carry that forward with underlayment, but the plywood institute says no, but a gap won't hurt.
4. 1/4-1/2" is fine...whatever you need to still let the baseboard cover it...same with the tile on top.
5. Ply ends at 1/4-span the space between the joists. That helps to isolate any jacking that may occur over them at plank ends from transferring through the underlayment.
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Unread 06-07-2020, 04:00 PM   #26
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I was able to get a good measurement of the beam deflection using a dial indicator.
That being said my reading was well under half the deflection of what the L/360 would be, and much less then what was calculated for the beam.
This is not surprising as there are 7/8" plank subfloor and 3/4" hardwood over the beam. So a large amount of the load would have been transferred to the
adjacent beams. And unless I removing everything down the the bare beam,
I can't get an absolute measurement of beam deflection.

That being said, I was more wondering about the relative change or stiffening
of the beam (floor joist), as I added things to stiffen the floor.
First I added 23/32 plywood to both sides of the beam, but only for about 1/3
of the beam length, mostly in the center of the beam.
The beam sagged about 1/2" in the center so I put some upward pressure on it with a jack post, taking out about 1/4" of the sage before sistering on the plywood.
I let it sit for a few days before removing the jack post and measuring again.

I was a little disappointed when my measurement did not show any improvement in the beam deflection, I got about the same numbers. I then
took measurements at each end of the beam a few inches from the seal beam, to make sure there was not much movement at each end, and there wasn't. I really think that adding the plywood would have stiffened it some.
The only thing that I can think of is that by jacking the beam up a little that
now there is some small upward flex in the subfloor and that now much less of the load is being transferred to the adjacent beams.
Also, nothing was done to the adjacent floor joists yet.

But I went one to my next phase. I placed Simpson CS14 across the bottom
of the beam (floor joist). I used a good bead of PL Premium and used the Simpson nails(they fit snugly into the holes), about every 4". These was plenty of squeeze-out and was messy. I had to clean up after about every
nail I put in, I went through lots of paper towels.

So, now I am letting that cure for a few days and will then see what the measurement shows. Although I did use the jackpost again when I put on
the strapping.

Thanks,
Jim
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Unread 06-07-2020, 04:32 PM   #27
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Jim, you can go to whatever length you like trying to measure your joist deflection, but it is much simpler to stay with the design deflection calculations based upon your known structure.

Adding plywood to the side of a dimension lumber joist does little or nothing to reduce deflection. If you look at the plies in your plywood that are oriented in the proper direction, I think you'll recognize that you're adding something close to nothing at all, 'specially when you consider that you can't sister any more than 8 feet of your 13+ foot joist. That's not even the absolute minimum of 2/3rds of the center of the joist.

But again, your wheel has long since been invented. If you want to stiffen the joist structure, there are know effective methods of doing that. If you want to try something else, that's up to you, but I think you're mostly spinning your wheels, to further torture the metaphor. Perhaps your metal strapping will help, but I'm not sure you'll ever actually know, 'specially in the long term.
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Unread 06-07-2020, 05:01 PM   #28
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I was at first hesitant in using 1/2" plywood, because of thickness added.
But now I calculated the deflection of 15/32 plywood
and 19/32 plywood and, well, by the numbers 19/32
looks to have half deflection as 15/32, so twice as strong
so to say.

What is your real world experience, does 19/32 seem to
be significantly stronger then 15/32?
How strongly would 19/32 be recommend over 15/32?
BTW. This is covering a 7/8" plank subfloor.

Thanks,
Jim
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Unread 06-07-2020, 05:28 PM   #29
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Over planks, the main reason for adding plywood is to isolate the tile from the seasonal movement of solid wood materials, not for additional strength. The industry says 1/2" nominal works. So, maybe if your planks are on the diagonal, the thicker ply might be useful, but otherwise, it's your call. You could split the difference and go with 5/8", which all by itself, is sufficient for a subfloor with a ceramic tile when installed properly.
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Unread 06-07-2020, 05:41 PM   #30
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Some people have laminated 2x material to the bottom of their joists, sort of like the configuration of an I-beam, but only on one side. That lowers the ceiling below, though, and may not be a great idea.
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