kitchen subflooring question

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Old 09-03-15, 12:01 PM
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kitchen subflooring question

I'm getting ready to install tile flooring in my kitchen and my sub floor is in two layers. Base is aprox 1/2" OSB and 1/2" particle board. It is very dificult to remove the particle board because it has been nailed and glued with what looks like a S pattern down to the OSB. Can I put down a 1/4" sheet of backer board on top of the particle board, or will I need to tough it out and chip away at the 1/2" sheet of particle board? If I do need to remove it, is the sub floor sturdy enough just having 1/2" OSB with 1/2" backer board? Any help or recommendations would be great!
 
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Old 09-03-15, 12:07 PM
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Welcome to the forums.

Get rid of the particle board. Then tell us exactly how thick the OSB is plus the size, spacing and unsupported span of the floor joists.

Ceramic tile or natural stone?
 
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Old 09-03-15, 12:15 PM
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Agree the particle board needs to go to the dump. It is too unstable for tile and the first spill and it swells. To remove, set a circular saw to the depth of the Particleboard. Make a series of cuts directly adjacent to the row of nails holding it down. Then cross cut into 2 foot long pieces. Use a pry bar to get under the particleboard on the side not nailed down pry up and use the leverage of te board as a hinge to pry up the nails and bend them back on themselves. It will save you a tone of time.

Plan on a minimum floor thickness of 1 1/4" before you add 1/4" cement backer board, so add 3/4" to your 1/2". Backerboard is set in a bed of mortar that is mixed from a powder not a ready mix.
 
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Old 09-03-15, 07:03 PM
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Levi,

The particle board belongs in a landfill, where it'll rot away in no time.

Originally Posted by Levi
is the sub floor sturdy enough just having 1/2" OSB with 1/2" backer board?
Absolutely not.

Concrete backer manufacturers (and industry standards), tell you that ⅝" ply or " OSB subfloor grade is enough as the base for their backer or membrane such as Ditra. I would not want just ⅝" unless the joists were @12" oc or less. Of course the thicker the better, so why not trash the PB and install min. ⅝" ply over your OSB, then either " CBU or Ditra which is ⅛" installed.

Before we go any further you should answer stickshift's questions about the OSB and the joists.

Jaz
 
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Old 09-04-15, 07:52 AM
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Okay, the floor joists are 2x10 and they are 16" apart and OSB is 1/2". Ideally I would like to keep the kitchen floor to hallway flooring as level as possible. I am planning on either porcelain or ceramic tile.

The hallway to the kitchen is going to have the original 1/2" OSB and 1/2" particle board with wood laminate flooring which is 8mm (.315").
 
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Old 09-04-15, 08:38 AM
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Levi,

You forgot to include the unsupported span of the joists. Any chance you know their species and grade, do you see any markings? What is the age of the home?

Jaz
 
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Old 09-04-15, 09:06 AM
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When you say unsupported span are you talking about the space between the Joists? If so it is 16". I am not sure as to the type of lumber used. Home was built in 1984.
 
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Old 09-04-15, 09:53 AM
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Unsupported span is how far do the joists run between posts or walls which keep them off the ground (or support them against gravity)?
 
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Old 09-07-15, 06:14 PM
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Levi,

What you described is the spacing of the joists. Stickshift pretty much described what the span means. Let us know when you're back from the holiday weekend.

Being that the house was built in '84, I'm sure the joists meet the min. specs for deflection. But it might be the min. for regular flooring, not ceramic tiles. Just wanna check so you don't have to re do this in 5 years.

Jaz
 
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Old 09-11-15, 09:06 AM
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Okay, I crawled under the house to the kitchen area and I have foundation from one outside wall to the entryway of the kitchen @ 15'. I have foundation at the back door (in the kitchen) to my living room foundation @ 10'.
 
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Old 09-11-15, 11:43 AM
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I guess you're saying part of the framing has 2x10" joists that span 15' 0". They're spaced 16" oc and the joists are unknown species and grade.

Your floor meets minimum building specs for general residential flooring, but it's kinda shaky for ceramic. I'd want the span to be under 13' for most species grade #2. This would take you around 50/20 psf live/dead load that I think is safe for ceramic. Min. code for regular flooring is 40/10 psf.

Not saying the grout will definitely develop hairline cracks or a few tiles might crack, but it's more likely to happen. Is there any way for you to make the span shorter or can you install a supporting beam across the joists?

Jaz
 
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Old 09-11-15, 12:51 PM
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When they built a spare bathroom in the house they reinforced the floor with what looks like a concrete deck block and a pressure treated 4x4. I could possibly do something like that if needed.
 
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Old 09-11-15, 04:46 PM
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Yes, that's the idea to reduce deflection. How does the floor feel now?

Jaz
 
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Old 09-14-15, 12:33 PM
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It felt fine when I had the original click lock wood laminate in there.
 
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