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Old 04-19-2013, 11:36 AM   #1
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Under plywood


Hi all, I have a question about my subfloor. Currently I have pine planks on top of the joists for the first layer. I would like to tile this floor so am adding 3/4 cdx on top. My question is can I lay down some 2x4 on the planks and then add the plywood on that instead of directly on theplanks? I have various reasons I want to do this... Also this is small room probly 10-15 sq feet floor ..


Last edited by busyhammer; 04-19-2013 at 11:39 AM.
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Old 04-19-2013, 12:37 PM   #2
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Ayuh,.... Donno if it'd work or not,...

Yer raisin' the floor, 4, 1/4", vs. 3/4", 'n the plywood will have more flex, due to the space, insteada full support from below...

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Old 04-19-2013, 12:46 PM   #3
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Originally Posted by Bondo
Ayuh,.... Donno if it'd work or not,...

Yer raisin' the floor, 4, 1/4", vs. 3/4", 'n the plywood will have more flex, due to the space, insteada full support from below...
I've got the plywood down and there's really no flex at all.. I think it's because I'm keeping the plywood sheets relatively small.. 40x40 at most... Also the 2x4 are spaced fairly evenly throughout..

Not sure about 4 1/4 number... I am raising the floor by 2 inches .. The plywood will be there no matter what... I have to do it this way because there is some plumbing in the floor and I don't want plywood touching pipes
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Old 04-19-2013, 01:04 PM   #4
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Originally Posted by busyhammer View Post
I've got the plywood down and there's really no flex at all.. I think it's because I'm keeping the plywood sheets relatively small.. 40x40 at most... Also the 2x4 are spaced fairly evenly throughout..

Not sure about 4 1/4 number... I am raising the floor by 2 inches .. The plywood will be there no matter what... I have to do it this way because there is some plumbing in the floor and I don't want plywood touching pipes
Ayuh,.... Yer layin' the 2x4s down,... 1, 1/2" + 3/4" is 2, 1/4"

3, 1/2", 'n 3/4" is where I saw the 4, 1/4"s... stood on edge...

yer gainin' alota inches of support by layin' 'em flat too...

Probably need a Tiler to really answer ya, for sure...
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Old 04-19-2013, 01:11 PM   #5
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Quote:
Originally Posted by Bondo

Ayuh,.... Yer layin' the 2x4s down,... 1, 1/2" + 3/4" is 2, 1/4"

3, 1/2", 'n 3/4" is where I saw the 4, 1/4"s... stood on edge...

yer gainin' alota inches of support by layin' 'em flat too...

Probably need a Tiler to really answer ya, for sure...
Reason I feel ok with this is the old floor i took up was done that way with the only difference being that it was 1x2 vs 2x4 .. And it was pretty solid
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Old 04-19-2013, 01:17 PM   #6
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CDX should not have been used under tile, it's full of voids in the core.
Why would you use 40 X 40" pieces Now the floors full of unsupported seams.
It should have been full sheets of T & G plywood underlayment rated or Advantec with constrution adhesive on top of the 2 X's.
There also should have been screws add to those old floor boards before any thing went down.
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Old 04-19-2013, 01:30 PM   #7
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Originally Posted by joecaption
CDX should not have been used under tile, it's full of voids in the core.
Why would you use 40 X 40" pieces Now the floors full of unsupported seams.
It should have been full sheets of T & G plywood underlayment rated or Advantec with constrution adhesive on top of the 2 X's.
There also should have been screws add to those old floor boards before any thing went down.
I could still do this since I have not nailed or screwed anything yet. Two questions..

1) it's a small space so I will have to cut the plywood to fit.. Is cut t&g the way to go then? I can't find advantec anywhere around here..

2) so the 2x4 is ok as Long as its glued as well as nailed to the ply?

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Old 04-19-2013, 01:41 PM   #8
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First check to see if the old floor is flat, if not that needs to be fixed first.
Add screws to the old subfloor.
Form a border with 2 X 4's around the outside of the room so all the outside edges get fully supported.
Add 2 X 4's on top of each floor joist, just use 3" ring shank nails or ceramic coated decking screws.
Add T & G plywood set in constrution adhesive.
Once again used ring shank nails.
Any lumber yard, Home Depot or Lowes I've ever been in carrys Advantec.

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Old 04-19-2013, 01:53 PM   #9
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Quote:
Originally Posted by joecaption
First check to see if the old floor is flat, if not that needs to be fixed first.
Add screws to the old subfloor.
Form a border with 2 X 4's around the outside of the room so all the outside edges get fully supported.
Add 2 X 4's on top of each floor joist, just use 3" ring shank nails or ceramic coated decking screws.
Add T & G plywood set in constrution adhesive.
Once again used ring shank nails.
Any lumber yard, Home Depot or Lowes I've ever been in carrys Advantec.

Please go back and add your location to your profile.
Just go to Quick links to edit.
Great info joecaption I really appreciate it.. I will try to do advantec but otherwise t&g ply if I can't find it. The pine planks are in good condition as they are newly added as part of this project., the old planks had some water damage so we decided to start fresh.. I'm just north of Chicago and been to lowes menards and hd but no luck with advantec.. No one in the stores has even heard if it..
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Old 04-19-2013, 03:29 PM   #10
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Quote:
Originally Posted by joecaption
First check to see if the old floor is flat, if not that needs to be fixed first.
Add screws to the old subfloor.
Form a border with 2 X 4's around the outside of the room so all the outside edges get fully supported.
Add 2 X 4's on top of each floor joist, just use 3" ring shank nails or ceramic coated decking screws.
Add T & G plywood set in constrution adhesive.
Once again used ring shank nails.
Any lumber yard, Home Depot or Lowes I've ever been in carrys Advantec.

Please go back and add your location to your profile.
Just go to Quick links to edit.
Hi joe quick question.. For the nails... I'm assuming they would be galvanized... And also does the thickness of the nail matter? Thanks againg for all the help
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Old 04-19-2013, 05:23 PM   #11
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No need for galv., 8 D will work as long as there ring shanked nails.
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Old 04-19-2013, 05:34 PM   #12
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Quote:
Originally Posted by joecaption
No need for galv., 8 D will work as long as there ring shanked nails.
Is no galvanized ok if the room is small bath ?
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Old 04-19-2013, 05:39 PM   #13
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If you do the rest of the job right those nails will never see water.
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Old 04-19-2013, 05:47 PM   #14
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Quote:
Originally Posted by joecaption
If you do the rest of the job right those nails will never see water.
True, so galvanized for the cbu but not ply, makes sense to me.
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Old 04-19-2013, 06:20 PM   #15
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Originally Posted by joecaption View Post
No need for galv., 8 D will work as long as there ring shanked nails.
8d through a 2x?

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