Introduction: Repairing Holes in Kitchen Plywood Sub-Floor

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First, the problem.

The previous owner had remodeled the kitchen and left a variety of holes in the wooden sub-floor where he had removed and or moved heating registers, plumbing and wiring. His patch jobs were amateurish and sloppy at best. Since he had covered his mess with a ‘click to install’ laminate flooring over an underlay/padding, his ‘work’ was effectively hidden from sight until we decided to remodel using a vinyl sheet flooring which would ‘telegraph’ his rough edges and gaps through to the surface of the new vinyl flooring.

So, each of the holes he had patched up or that were left when we changed the cabinet layout and removed a Dishwasher Island, had to be repaired so as to leave a smooth surface wherever we intended to glue our new vinyl floor covering.

To repair each opening, a new piece of sub-floor of the same thickness as the old sub-floor plywood had to be cut to fit the holes exactly – as tightly as possible and effectively ‘tied’ to the existing sub-floor so as to withstand the daily foot traffic expected in the kitchen.

Step 1: Gather Ye Tools


1/2" top bearing flush trim pattern bit

Drill Driver - I like the Craftsman 19.2 volt C-3 with clutch (Not shown)

Shop Vac (or use the wife's)

Sharp Knife - I used one of the retractable types with break away blades (not shown)

Heavy weight - I lucked out finding a 4 x 6 x 8" block of steel years ago that does the job perfectly

Saran/Plastic Wrap

Paper towels

Wood Glue - water proof if you've got it!

Four wooden boards cut to fit largest opening to be patched (I used 1/2" thick material cut as wide as half the diameter of my router base - use hardwood or hard plastic if you've got it)

Wood putty / wood filler - I like the Rock Hard stuff shown and it goes a long way - the container shown is at least twelve years old and I have some left!

Wood screws long enough to fasten the wooden boards (above) to the wood floor you are working on.

Screwdriver or small pry bar.

Step 2: The Inspiration - Was a Router Table Insert

I had learned to cut an opening in a wooden table top that would accept a rectangular router base years ago when I made my first router table.

You take the rectangular piece you want to insert and use it as a pattern to route an opening of the same size using a flush trim, top bearing router Pattern Bit.

You lay the piece you want to insert on the surface of the wood it is to ‘go into’ and ‘frame it’ with four boards the router base will rest upon while the interior edges of which will serve to guide the pattern bit that will cut the opening exactly the same size as the pattern piece used.

Step 3: Make Your 'pattern Piece'

Cut a square or rectangular piece of (in my case plywood) of the same thickness as the plywood flooring to be patched so it is at least (IMHO) a half an inch larger all around than the hole to be patched - more is better, of course.

Although it does not need to have perfect 90 degree corners - I shot for such perfection.

Step 4: Position Your 'pattern Piece' and Frame It!

Center it over the opening/hole to be patched.

Then, one at a time, add each of the guide boards screwing each down before adding the next.

Note the pattern of the guide boards. One 'end' of each guide is flush with the respective side of the previos ly installed pattern piece. The extra length of each guide serves to help locate the next.

Because, if you do this properly, the pattern piece will be held rather tightly by the guides, adding two screws into the pattern piece (driven only part way in) serve as 'handles' to help remove the pattern piece so you can move on to the next step.

Step 5: Set Up the Router

Forgive me, I forgot to take a picture to help illustrate the following.

You have to set the depth of the router bit before you can rout out the opening for your patch.

The correct depth is equal to the thickness of the patch material PLUS the thickness of your guide boards.

So, turn your router upside down and take your patch and one of your guide boards and lay them together on the router base.

Then, adjust the depth of your router bit so that it is EXACTLY the same as the the two pieces are thick. Since your patch material is exactly as thick as the flooring material you are cutting into and the router rides on top of the guide material, you will cut out just the thickness of the top layer of your sub-floor - no more.

Step 6: Rout the Opening for the Patch

Place the router such that the bit is in the hole you want to patch and turn it on.

Move the router slowly toward one of the guides.

When the bearing contacts the guide edge, move the router slowly along that edge in a CLOCKWISE movement until you contact the next guide at the first corner.

Continue moving the router along the next guide CLOCKWISE until you return to the point of beginning along the first guide.

Hold the router steady and turn it off.

After it stops, lift it up and out of the opening.

Remove the material in the center. You may have to take a sharp knife to cut it free, leaving some slivers which (IMHO) may serve to help glue the patch in place - so leave them as I did or remove them as you see fit.

The patch fits side to side, but (step 7) ...

NOTE: Some may prefer using a PLUNGE BASE on the router and setting several depth stops, This is (in my case) a rather heavy (deep) cut to be making in a single pass. I suspect quite a few furniture makers would want to make two or three passes using as many depth stops on the plunge base. In my case, I felt it would serve me better if I only went round one time. And, In my case, it seems to have worked just fine.

Step 7: Round the Patch's Corners

As I suggested, your patch has perfect 90 degree right angle corners but the opening you cut has perfect 1/2" diameter round corners! Curiously the same as the diameter of the trim bit employed!

So, take a drill guide or similar 1/2" template and mark each corner of the patch to guide you when sanding the four corners of your patch to match - poetry!

If you sand carefully, your patch will fit nicely and precisely into the opening you made with your router and you will be so proud of yourself. (Ask my wife how I know this)

Step 8: Install the Patch

Get your Wood Glue and apply a generous line around the edges of the opening you routed and, then a bead along all for edges of your patch and press it into the opening.

Cover the patch with a sheet of cling film (Saran Wrap, or use a plastic grocery bag).

Cover that with a few thicknesses of paper toweling.

Cover that with your CHUNK OF STEEL weight. Or whatever dense material you can find that distributes the weight on the patch piece without touching the surrounding floor. If the base of your weight is larger than your patch, use a piece of material equal to or slightly smaller than your patch piece to elevate the weight(s) so they only weigh your patch down.

Let the glue dry as long as you have patience, then add a hour or so to be safe.

Step 9: Finishing Touches

Remove the weight and paper toweling and cling film to reveal your work.

I took a belt sander to remove the glue and generally smooth the patch and surrounding floor. Go lightly! You just want a smooth and level surface - don't create a depression!

Then I filled any openings and screw holes with Rock Hard Water Putty. Let it dry and, the next day, sanded off the excess putty. (oops, forgot to take a picture first!)

In all, I patched about seven openings this way.

Looking good.

Step 10: