Adding new sub-floor over old particle board

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Auggie
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Joined: Sun Apr 07, 2013 8:36 am

Adding new sub-floor over old particle board

Post by Auggie » Sun Apr 07, 2013 8:48 am

I just bought a 1991 manufactured home that is on a permanent foundation with permanently attached garage (the park is manufactured home park and not a mobile home park).

Most of the flooring in the "wet" rooms have been damaged so my plan is to properly cutout and replace all damage and mold, then overlay the entire house with new 3/4" T&G OSB because there are many soft spots in the living room, dining room (both adjacent to the kitchen) and master bedroom (which is open to master bathroom). All carpet and vinyl flooring is unserviceable and I want to replace all trim anyways so the only additional work is shaving/replacing doors.

I posted a question of this process in a DIY forum and someone has been strongly opposed to "adding" an entire new sub-floor over the existing one because he explains that the frame and outriggers cannot handle the additional weight and will eventually cause the frame to buckle. He qualifies his statements by saying he's "worked in the MH industry for years." Thus, he recommends I cut out the entire sub-floor around the walls and "sister" in 2x's and blocking to support the ends of the new sub-floor. Whew, that seems like a LOT more work.

On other forums, I've read numerous advice from others that overlaying a new sub-floor over an existing one is recommended many times over.

So who is right? Who am I to believe?

David Oxhandler
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Re: Adding new sub-floor over old particle board

Post by David Oxhandler » Sun Apr 07, 2013 7:04 pm

Overlaying already compromised particle board decking is a mistake, because once particle board absorbs moisture the decking will continue to decompose until the wet portion is cut out.

When we renovate homes that were built with particleboard decking, I prefer replacing only the damaged and "soft spots" in the floor decking with new plywood. Overlaying all the floors will probably not create any support problems but it seems to be a bit of "overkill" and over expensive.

If you want some protection for the particleboard in the unaffected "dry" areas it will be a lot less expensive to paint the existing decking with a marine paint, Kilz or other top grade oil based paint that will prevent interior moisture from compromising the decking.
David Oxhandler
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Auggie
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Re: Adding new sub-floor over old particle board

Post by Auggie » Mon Apr 08, 2013 6:36 am

Thanks for the advice, especially coating the existing sub-floor.

The reason for my initial plan of overlaying the entire house is because there are just too many "spongy" soft areas in the dining room, living room, and master bedroom. So instead of trying to target patch all the suspect areas I want just do it all to give everything a solid feel with no worries for future issues. I will make my final decision once I pull all the finish flooring and carpet to visually inspect the suspect areas.

I just want to clarify that I DID explicitly state that I AM going to replace any damaged wood any traces of mold; but it seems everyone always jumps to conclusion and believes I'm trying to cover up the damage. (sigh)

David Oxhandler
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Re: Adding new sub-floor over old particle board

Post by David Oxhandler » Mon Apr 08, 2013 9:43 am

I had not considered a "cover up".

You must cut out any areas that are even slightly effected. Particleboard is like a sponge and once it absorbs moisture, and the damage continues to spread like cancer, until it is cut back to solid, "uninfected" decking....

That said ... you do need to target and patch all the effected areas, regardless of what you do next. The critical skill here is to avoid humps and dips in the finished floor... getting the "patches" to have the same top elevation as the existing good floor decking so that you can install new floor covering of your choice.

In areas where you will install carpet this presents little difficulty. In areas where you intend to install vinyl or tile or other coverings that requires a perfectly flat deck, that wont show seams, we overlay with quarter inch plywood. This leaves none or minimal problems with door bottoms, etc.

The overlay gets counter screwed (head of screw below the top). Seams and screw indents are skimmed with floor leveler product you can find at any home improvement store. Pay attention to the installation instructions, especially when your plans calls for vinyl. Some wood filler and floor leveling products will bleed through vinyl over time leaving ugly stains in your new vinyl.

Download The Manual for Manufactured Home Repair & Upgrade. You will find a detailed chapter on floor repair and replacement.
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David Oxhandler
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Auggie
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Re: Adding new sub-floor over old particle board

Post by Auggie » Mon Apr 08, 2013 10:05 am

Even better tips, thanks!

No vinyl will be installed: just carpeting and tile (kitchen, bathrooms, and laundry room). I am going to put down 1/2" cement board for the tile; I'm assuming this would be in lieu of 1/4" plywood that you suggested for vinyl floor covering.

trmimo
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Joined: Tue Sep 12, 2006 9:54 am

Re: Adding new sub-floor over old particle board

Post by trmimo » Tue Apr 09, 2013 5:14 am

David's advice is good. If you are worried about it you can use the 1/4" plywood throughout the house. This is a great way to make the marriage line smooth.

Auggie
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Re: Adding new sub-floor over old particle board

Post by Auggie » Tue Apr 09, 2013 7:53 am

Yes, I've been now thinking of going to 1/4" plywood throughout, with 1/2" cement board instead under tiled areas.

karen123
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Re: Adding new sub-floor over old particle board

Post by karen123 » Wed Oct 14, 2015 3:50 am

We got an education in subflooring when we tiled our bathroom recently, too. We were expecting particle board when we pulled up the carpet, but found OSB instead–a term I’d never heard before (I always thought of that stuff as “that gross kind of particle board with, like, all those things in it?”) This post is making me extra relieved that that’s what we have; it’s ugly, but you can tile over it! Good luck, and good choice hiring someone for part of the job :)

GeneralManager
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Re: Adding new sub-floor over old particle board

Post by GeneralManager » Mon Nov 02, 2015 4:32 am

i think when we renovate homes that were built with particleboard decking, I prefer replacing only the damaged and "soft spots" in the floor decking with new plywood.

Electrical repairs

GeneralManager
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Re: Adding new sub-floor over old particle board

Post by GeneralManager » Mon Nov 02, 2015 5:35 am

i think when we renovate homes that were built with particleboard decking, I prefer replacing only the damaged and "soft spots" in the floor decking with new plywood.

Electrical repairs

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