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Old 03-10-2019, 11:55 AM   #1
Carla C
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1957 bath floor deflection

Hello, it's been a long time since I've posted but I'm so glad this forum is still here!

We are renovating the baths in our 1957 home. We recently bought it from the original owner, who built it and never changed a thing. We have a pink bathroom and an aqua bathroom, leaking and worn out. We'll totally gut, replumb, etc.

I'm making materials choices and want to make sure things are in order with floor deflection. The floor joists are 9" x 1 5/8", 16" oc, span 12'3". Deflecto says that's 472, good enough for tile but not stone. But deflector didn't even ask about subfloor!

The subfloor is 1x6 set on a diagional. I'm guessing I'll need to tear that out and put in 3/4" plywood, no matter what else I do?

The tile I'd like for the hall bath floor is Emser 12x18 porcelain in a terrazzo style. It's very thick.

In the master bath I was hoping to use stone on the floor, but I could be persuaded to use porcelain if needed.

I'd appreciate any feedback about the plan so far and how I should proceed.

Thank you!
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Old 03-10-2019, 12:18 PM   #2
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Welcome back, Carla.

You could treat that subfloor the same way we recommended back in 2017 and add a layer of minimum nominal half-inch plywood and your tiling substrate of choice. The tile industry standards require that for a sawn board subfloor of 3/4" thickness, but that presumes the boards are laid perpendicular to the joists and are T&G style. In your application I would recommend you increase the plywood to nominal 5/8ths", but that's not in the book.

Or you could, as you suggest, remove what you have and start over with nominal 3/4" plywood and the tiling substrate of your choice. That would also give you the opportunity to bring the joist tops into plane for the very flat floor you'll need for those large format tiles.

I would not recommend natural stone given your joist deflection, but if you elect to do that anyway you'll need to add a second layer of plywood before your tiling substrate.

My opinion; worth price charged.
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Old 03-10-2019, 01:08 PM   #3
Carla C
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Oh, good, it sounds like I could just use 3/4" plywood, ditra, and then the porcelain? That would put my height very close to the adjoining hardwood floor.

How would I bring the joist tops into plane? And if I have everything torn off above the joists, maybe the joists will rebound up a bit, compared to putting them under the weight of the built bathroom? So how do I know what is "in plane" when the joists have no load?
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Old 03-10-2019, 04:00 PM   #4
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Joist tops may already be in plane, Carla, can't tell from here, eh? You want to get the longest straightedge that will fit across the joists (perpendicular to them) to check that. Just lay the edge across the joists in several places and ensure that all the joist tops touch the edge. Also good to check along the length of the joist to see that they are flat on top.

If not, you can sister some 2x6 material against the joists to make them all be in plane, and even level if you care about that. Your tiles don't, but they do care about flat. Bigger the tile, more they care.

My opinion; worth price charged.
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Old 03-12-2019, 02:50 PM   #5
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Thanks!
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Old 05-17-2019, 09:43 AM   #6
Carla C
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A question about deflection and subfloor

I've been searching posts about deflection and I've been to Deflecto, and I'm finding info about the joist size and spacing. I'm not finding much about subfloor specs. My subfloor is 1x6 planks set on diagonal (not t&g, maybe shiplap?). My deflection comes out at 672 for 2x10 joists, 16" OC, 12' span. I'm planning to tear the subfloor out and install 3/4" exterior grade plywood, then ditra, then 12x24 porcelain tile. I'm replacing subfloor to keep total height close to the adjoining 3/4" oak floor over 1x6 diagonal planks. Am I going overboard? Is there a better way that avoids tearing out subfloor?

Thank you.
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Old 05-17-2019, 10:04 AM   #7
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The only other option I can see, Carla, is to go over the 1X6 with a layer of 1/2" plywood, screwed to the planks (and after you screw the planks to the joists). But that will put your finished tile floor above the adjoining hardwood flooring.
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Old 05-17-2019, 10:36 AM   #8
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I've combined you with your original questions on this subfloor, Carla, and our recommendation isn't likely to have changed much.

A single layer nominal 3/4" T&G plywood subfloor over joists on 16" centers will meet the minimum requirements of the manufacturers of all ceramic tiling substrates of which I'm aware.

Schluter Systems makes a Ditra XL, which is taller than their Ditra and was designed at least partially to meet the very application needs you have in trying to match the height of adjoining hardwood flooring.

Depending upon your tile thickness, you might also consider using a 1/4" CBU as your tiling substrate.

My opinion; worth price charged.
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Old 05-17-2019, 11:02 AM   #9
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It might not feel like it while you're working. But the results of the extra work are worth it to most folks who value smooth transitions.

But do take a look at where your joists are...they may not fall in a very convenient place to allow a full subfloor removal.

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Old 05-17-2019, 11:03 AM   #10
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Thank you.
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Old 06-07-2019, 09:18 PM   #11
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I got the 3/4" plywood in. It's pretty stiff but maybe not as solid as floors where I've done plywood over existing planks... so I'm a little nervous about it. But Ditra says it's ok for ceramic. My handyman put it in with nails but I'm not sure what kind. If they are ring shank it's fine, right? If they are not, I should go back and add screws? Schluter doesn't give specific screw spacing for 3/4" subfloor like it does when you are putting 1/2" plywood over a subfloor, does it matter?

The tile I want to use in one bath floor is a really thick cement(?) terrazzo. Would that be more like tile or stone?

Thanks!
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Old 06-08-2019, 05:32 AM   #12
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Hi Carla,

I’d have expected the subfloor that was installed directly over the joist to be glued and screw with 12”-15” spacing.

Personally, I don’t like using nails since they have a tendency to walk out over time especially if installed without adhesive.

I’d go ahead and install 2” grip right deck screw every 12”. Leave the nails but make sure they are flush top to top with the subfloor.

How did you attach the plywood over the old subfloor?


Sorry, but I can’t answer your question on the tile type; I’ll leave that to one of the site pros.
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