Subfloor Repair

"How-To" information for repairing a subfloor

Need some help with subfloor repair?

While there is some skill work involved with this procedure, it's something that anyone can do with the right tools and a little bit of patience.

The main aspect of the job is to remove the old, damaged stuff so that you can get at your specific repair area and see what exactly needs to be done. It can get a little dirty, so be sure to use your protective wear, especially considering you're going to be handling dirty, splintered, and rotted (possibly moldy) plywood (or something else if the house is real old) for your subfloor repair.

Out With The Old, In With The New

tools and materials for subfloor installation

Tools an Materials
You will need a pry bar and a hammer for doing the demo work, some 2" x 4" stud pieces to use as joist supports, some flat-head coated sinker nails (1 3/8") to secure luan underlayment, coarse drywall screws (1 1/4") to secure OSB flooring repair piece.

The good news is, you will be getting the worst part out of the way first. It's always easy to tear out something, but you need to be careful in the process as you will have to handle rotten wood filled with old nails and wood splinters everywhere. So it's probably a good idea to wear leather gloves to protect your hands. It took a while for me to get this (safety step) into my head, but after jamming splinters into my hand for umpteenth time, I figured it was, after all, a good idea! Oh, and wear some safety goggles too.

picture of old asbestos vinyl tile

Use the pry bar and hammer to remove the old stuff such as any shoe mold and baseboard that might happen to be there. Some people don't like to do this: I prefer to demo this way because it allows you to remove everything, and basically allows you to start with a clean (debris-free) area to work with. Then, when you have the base and shoe gone, remove any old vinyl and /or tile that may be present (like what you see pictured).

At this point you might be kicking up a lot of dust, so it's probably a good idea to wear a respirator type mask (see above protective wear link for more details) to keep from breathing fine dust in the air.

You will, at any rate, uncover the damaged subflooring. When you do, you will most likely be able to pinpoint where the rotted flooring is, and basically be able to simply pull up the damaged material rather easily with your pry bar. This step will also enable you to see where exactly the floor joists are are, and how you can go about the process to to configure your exact repair measurement.

Proceed to remove the rotted part of the floor.

Note
If you have to cut only a portion of the floor, do the following:

Determine where the rotten wood ends, and the stable wood begins and proceed to the next available floor joist to use as your repair support.

Take a hand power saw, and set the blade depth to the height of the subfloor itself. This will only allow you to cut to exactly the depth of the floor, and nothing else.

Cut the floor down the middle of the floor joist (using guide marks drawn on the floor or wall) to reveal half of the floor joist. You will then add another 2"x 4" support piece.

Make sure to pull out all the old nails and staples that might be still attached to the floor joists. Rub your hand along the top of the joists, in the corners and along the edges (where the base and shoe mold were) to see if there are any nails still embedded. When you're done with that, vacuum the entire area.

Add 2" x 4" Support Pieces
Nail or screw 2"x 4" support pieces into place. Make sure they are exactly flush with top of the floor joist. The purpose of this step is only to provide something substantial to nail into, but to also allow the subfloor repair piece to rest firmly and solidly without the threat of sagging at some point in the future (which is what happened here in this particular repair scenario) thereby rendering you're repair useless.

picture of subfloor repair

Secure Subfloor Repair Piece Into Place
You will need to determine the thickness of the floor to see what you'll need to install. Some floors are 3/4 inch, while some may be 1/2 inch thick. When that has been determined, purchase the flooring at your local home-improvement store.

Tip
I prefer to use OSB flooring. This acronym stands for Oriented-Strand Board, this a fancy name for manufactured flooring material made out of shredded wood fiber. The good thing about it is it's ability to retain it's "flatness", as well as provide a really strong, solid base. And, I think it's just easier to work with than ordinary plywood. Plus, it's cheaper.

After measuring and cutting your repair piece, begin to secure to floor joists. Before you do this step, however, mark either on the wall, or on the floor (or both) where the joists are located. Mark down the centerline of the existing joist, along with center of the add-on 2" x 4" support pieces. This will enable you to have enough solid support area to secure to, and locate exactly where to do this. Place fastener (screw or nail) every 10 - 12 inches.

picture of subfloor repair

Install Luan Underlayment
I like to use 1/8" luan material as a nice smooth base for subfloor repair upon which to lay vinyl tile flooring (or any vinyl for that matter such as by the sheet, or the peel and stick type). Once nailed into place, the smooth solid surface easily accepts the vinyl tile pieces resulting in an unseen, but very substantial subfloor repair.

Use 1 3/8" coated sinker-type nails (pictured) with flat heads to prevent vinyl from laying perfectly falt onto the floor surface. Space your nail pattern every 6 to eight inches apart to prohibit the floor from buckling as a result of temperature changes, water damage, and other mishaps.

picture of subfloor repair

Subfloor Leveling
This step is similar to applying putty to small cracks in woodwork. Take your putty knife, and spread some floor leveler over any exposed cracks, splits, and minor depressions caused by excessive hammer whacks (which I do a lot!), and other things as a result of the subfloor repair installation process.

Don't be surprised if you use a fair amount of floor leveler in your subfloor repair work, as it's just a normal part of the process.

Do your best to fill all cracks as you want to have as solid a foundation as possible. Spread this leveler out to a smooth texture showing no ridges.

Allow the leveler to stand and dry for at least four hours. That's what the directions say for the type I use, which can be found at most any home-improvement store. I do, however, prefer to let something like this set-up and dry overnight, especially if it's a little heavy in areas. Don't be in too much of a hurry, or you'll just be wasting your time.

Well, that about does it for subfloor repair.

The thing to keep in mind in subfloor installation, is to clean up the finished luan area really well so as to keep the new vinyl to be laid from pitting and tearing as a result of dirt, pellet-sized debris, nails, etc., from finding it's way under the new floor as you are doing the installation. After doing all that work, all you would need is for something to try to poke it's way out of the newly installed vinyl. I've seen this happen before.

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