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Community and Q&A

Fixing Swollen Subflooring

Tapcon | Posted in General Questions on

Although Advantech and Legacy panels were used as a subfloor, there has been more than 2 months of rain and a really difficult time to get someone to install trusses and roofing. As a result, there are a lot of panel seams that have swollen. Can the seams be sanded with a belt sander to address the issue? If so, what grit — 60 ?

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  1. Expert Member
    BILL WICHERS | | #1

    Once the panels have dried, you can sand any raised edges. Make sure to check first though -- panels that are severely delaminated should be replaced.


  2. Expert Member


    Sand, or if the fasteners are sunk deep enough you can use a power planer. See how 60 grid does. You might want to get more aggressive and save time.

  3. Moderate | | #3

    This is a common issue with OSB floor sheathing. A remedy we have found to work well is to sand the entire floor using a rented, walk behind, rectangular oscillating floor sander. We do this after the drywall texture coat has been applied, just before priming the walls. The walk behind sander is much easier on the knees than spending a day bent over a belt sander, makes quick work of flattening the seams, and cleans any residual drywall mud off the floor as well. These sanders are very forgiving for this type of application, so use an aggressive grit, like 40, and your seams will be flat and clean in no time.

    1. Expert Member
      BILL WICHERS | | #4

      Have you had any issues with those sanders grabbing the edges of OSB and ripping out chunks? Just curious.

      BTW, it's recommended to seal any cut edges of OSB to protect against swelling if the sheet gets wet. I think many crews skip this step. If you seal the cut edges of panels when putting the subfloor down, it should help to limit how much edge swelling you get if you have any surprise rain before you have a roof up.


      1. Moderate | | #5

        The size and complexity of the projects we're on typically means a sublfoor may see an entire winter of weather before being dried in. Other than some swelling at the seams, the Advantech Edge Gold product works as advertised and performs better than any other material I have seen. Once it does dry, a few hours with the sander results in clean and flat floor. The rectangular walk behind sanders (typically 14" x 20" and also referred to as a floor buffer if you're using them with a buffing pad instead of sand paper) are gentle in their operation. They just oscillate back and forth, but with the weight of the machine and the aggressive paper, they act like a supercharged palm sander. The wide footprint of the machine results in a very flat seam, while knocking down any other little humps and bumps that may have developed, you just let the machine linger over the seams and other areas that need more attention.

        1. Tapcon | | #6

          Along the same lines as the previous commenter, would you have to check every inch of every seam to insure there are no screws above surface or only slightly below which would also rip the heavier sanding machine? (The guy that messed up the job to begin with put quite a few screws down that did not hit the joists. And those are sitting with heads just barely above the surface.)

          1. Moderate | | #7

            The rectangular floor sander/buffers utilize a thick cushion pad between the base of the sander and the paper, this allows them to move over the floor without snagging or catching. The sanding paper is quite thick, with a rigid backing, (especially in the heavier grits, like 20 or 36) so I would be surprised if a near flush screw head would have any effect on them.

            As an aside, screws that completely miss a joist are a minor nuisance and could likely be left in place if they are not sticking up enough to affect your flooring or underlayment, but errant screws that have made only partial contact with a joist could be a source of future squeaks once things dry out.

        2. evergreenhomes | | #8

          Does the manufacturer of your machine sell the sand paper? What model of machine do you use?

          1. coopersbuddy | | #9

            Typically wherever you would rent the machine (all the rental yards around here have them) would also sell the paper and backing pad. The style machine we use is shown in the attachment.

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