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Old 09-15-2011, 09:29 PM   #1
Mike K
 
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1/2" BCX glued over uneven floor.


I need to glue and screw 1/2" BCX plywood over my existing 3/4 bathroom sub floor to make it stronger and flatter. One joist is about 5/32 lower than the rest and Im not sure how to prevent the new 1/2" plywood from following the same low spot. Is there a gap filling glue I could spread thick in this low spot? Or shim it with 1/8 and then glue? Vinyl flooring will be installed over the new 1/2".

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Old 09-16-2011, 02:55 PM   #2
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1/2" BCX glued over uneven floor.


SLC, self leveling cement

Adding plywood in the hopes of removing the valleys and making the entire floor flat does not work.

You will be able to install the new flooring over the SLC without the need for more plywood if the present subfloor is in otherwise good condition.

Vinyl flooring in the bathroom huh.

Jaz

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Old 09-16-2011, 05:46 PM   #3
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1/2" BCX glued over uneven floor.


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SLC, self leveling cement


Vinyl flooring in the bathroom huh.

Jaz
SLC.. Thanks..

I had tile before and it failed because it was masticed onto the plywood. Grout cracked and allowed moister to sag the plywood after 40 years.
Your saying I should thinset CBU the floor, then add more thinset on top to the low spots to level the large tile I previously dreamt about Jaz? I dont want lippage. Seems to me CBU wouldn't conform to my plywood creating a hollow unsupported area over the low joist.

I have 3/4" T&G on 2x10's 16" oc 12' span. And a kerdi shower kit.
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Old 09-16-2011, 08:38 PM   #4
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1/2" BCX glued over uneven floor.


Quote:
I had tile before and it failed because it was masticed onto the plywood. Grout cracked and allowed moister to sag the plywood after 40 years.
I'm not surprised. What you describe is all wrong. It probably failed within the first year.


Quote:
Your (you're) saying I should thinset CBU the floor, then add more thinset on top to the low spots to level the large tile I previously dreamt about Jaz?
That is not what I said above, but then we were talking about vinyl. However you're close. If you go with ceramic tiles that method can work, but it's more work. Alternatively, if your subfloor is in good shape using the SLC is all you should need. Then tile over that.

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Seems to me CBU wouldn't conform to my plywood creating a hollow unsupported area over the low joist.
Actually CBU will conform more than plywood. But we don't use either to flatten the floor.

Please decide whether you want vinyl or ceramic. The answers to your questions will be a little different for each.

Jaz
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Old 09-16-2011, 09:10 PM   #5
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1/2" BCX glued over uneven floor.


Gluing down the plywood is a bad idea.
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Old 09-18-2011, 08:42 AM   #6
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1/2" BCX glued over uneven floor.


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Alternatively, if your subfloor is in good shape using the SLC is all you should need. Then tile over that.

Jaz
The subfloor is stained, but feels solid.. But when I lay a straight edge on it it looks like it's seen better days.

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Please decide whether you want vinyl or ceramic. The answers to your questions will be a little different for each.

Jaz
I would like tile. But I'm hesitant on anything other than concrete after reading and seeing first hand the failures on plywood.

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Gluing down the plywood is a bad idea.
Can you elaborate on that a bit? Wouldn't it be stronger? I mean, plywood is strong because the veneers are glued together..
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Old 09-18-2011, 10:35 AM   #7
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1/2" BCX glued over uneven floor.


Quote:
Can you elaborate on that a bit? Wouldn't it be stronger? I mean, plywood is strong because the veneers are glued together..
Rusty is right, since most people use construction adhesive from a tube to glue the top layer. The thick beads can create slight voids. However, if you can spread thin wood glue to cover 100% and get it down and fastened before it dries, go ahead and laminate.

Quote:
The subfloor is stained, but feels solid.. But when I lay a straight edge on it it looks like it's seen better days.
If the floor was once flat, but it's now warped, it can't be solid. We hear "solid" all the time, I don't know exactly what it means.

Quote:
I would like tile. But I'm hesitant on anything other than concrete after reading and seeing first hand the failures on plywood.
We don't recommend tile direct over plywood. Use a concrete backer or a matting such as Ditra. Tile works perfectly well over a wood framed base as long as you follow the rules.

Jaz
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Old 09-18-2011, 08:21 PM   #8
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1/2" BCX glued over uneven floor.


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The thick beads can create slight voids. However, if you can spread thin wood glue to cover 100% and get it down and fastened before it dries, go ahead and laminate.
If the floor was once flat, but it's now warped, it can't be solid. We hear "solid" all the time, I don't know exactly what it means.

Jaz
The plywood is.. sound. The plywood doesn't sag or warp. It's the joists which are slightly different dimensions. I measured 3/16" difference in joist height in my low spot. Must have been a monday or friday when they ripped my joists.

I do want tile, but need a flat strong floor. I have a deflection of L / 522 which say's good for tile, but not natural stone which suggests to me its boarder line.
http://www.johnbridge.com/vbulletin/deflecto.pl
How would you proceed Jaz?

Thanks
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Old 09-19-2011, 06:21 PM   #9
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1/2" BCX glued over uneven floor.


OK, so the joists are not in plane with each other. Were they always this way? Joists usually have a crown on one side, the crown goes up. Maybe one has a split and it dropped. Take another look under there.

If the floor is in otherwise good shape you can continue. Several choices: Either flatten the floor and then install Ditra. Or install a concrete backer then flatten the floor.

A deflection of L /522 is not border line for ceramic tile. It's well above specs. Remember this figure applies only to your joists, not the subfloor. So we believe you're at least halfway there.

Jaz
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Old 11-05-2011, 08:52 PM   #10
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1/2" BCX glued over uneven floor.


No splits. Just inconsistent joist dimensions.

I found a good tile installer who has suggested Ardex, Custom, Henry, or Mapei floor patch to fill in the low spots, and then add 5/8" plywood and ditra, or 1/4" hardieboard and tile. He is concerned that using slc may not level well since I want to continue the same tile.http://www.ceramicasantagostino.it/en/collezione/61
Throughout the rest of the home.

Is one of these floor patch materials a acceptable method?

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