This is my third time using plywood for a finished floor and I thought I would go into more detail this time than I did before. First I’ll briefly go over my reasons for using it:
Economy – At the current price of $36 per sheet, that just a little over $1 per square foot. When you add in the other costs (excluding labour) to finish it, the price goes up to just over $2 per square foot. Not bad for any finished wood floor.
As important as economy is, even more important to me is the way the product is installed. I will not use any flooring that “floats”, simply because you need to make clumsy transitions from it to another type of floor. A humped threshold from the hall to the bathroom, for example. That absolutely kills any kind of laminate flooring for me.
Additionally, the main floor of my house has infloor heating and that may be a problem for a traditional hardwood floor due to expansion and contraction. A softwood like pine may work better, but is double the cost of the plywood without any real advantages (other than to say: “look at my beautiful pine floor”). Also, you normally can’t (or wouldn’t want to) face nail hardwood, so you’d have to be very selective and careful where you drive the long staples that hold it down to avoid hitting a pipe.

The plywood itself is 1/2″ thick pine that is sanded smooth on one face. This is “AraucoPly” brand (no endorsement) and I believe it is manufactured in South America. As you can see from the picture, the face grain is very uniform and is relatively defect free. The plywood also appears to be void free, or at least I haven’t found any:

The first step in the process is to rip the 4′ x 8′ sheets in half to make them more manageable. I did this with my brother Don’s help on the table saw, but a hand held circular saw with a saw board would work as well:

I will say that I think the quality of this plywood has dropped since the first time I used it in my last house. When I did the plywood floor there, the sheets were much flatter and overall had fewer defects. I’m not sure if this decline in quality is a condition that will continue, but for the most part it doesn’t have much of an impact on how well the floor turns out. I had to use a few more nails to hold it flat to the floor and I had to cut out a few more defects in the face grain.

Here’s a better look at the edge. The face veneer is somewhat less than 1/8″ thick, but will still allow a lot of sanding before you break through to the layer below. The plys under are of the same wood, but lower quality and the glue bond is strong between layers – I’ve seen no signs of delamination on any of the sheets I’ve cut:

After the sheets were cut in half, I ripped them into strips that are nearly 4″ wide. This will give me 12 strips from a full sheet with no waste:

While I cut, Don chamfered the edges slightly with the trim router. The same can be done with a sanding block, or a block plane:

It doesn’t take long for the strips to stack up. The ends that butt together in the floor will be trimmed off and beveled slightly as well:

With enough strips cut to get started, we set up in what will be my office. As you can see, the floor is interlaced with PEX tubing that provides the heat for the room. I laid this on top of the existing floor, then infilled with 5/8″ OSB. The white and brown squares are thin aluminum plates that help extract the heat from the pipe. I made these from roof flashing and made a simple jig to bend them to fit snuggly around the pipe:

One major drawback with infloor heating is the ever present threat of accidentally puncturing one of the pipes. Sure enough, I did it while laying my first board:

I was filming at the time, and can blame that distraction for my blunder. Still, very lucky that more of the floor wasn’t down, since quite a lot of water leaked out and I had to stop for a day to let it dry out. I would have had to tear up and throw away any of the plywood that got wet.

The repair is simple with PEX, just add in a coupler and chop out the floor a bit to fit it in. I have no concerns about this ever leaking and the slight flow restriction doesn’t make any detectable difference:

The strips are laid tight to each other and are actually glued down to the sub floor using polyurethane construction adhesive. This can be done, since plywood does not expand and contract with seasonal changes like solid wood does:

Along with the glue, I used 18 gauge brads to hold it tight down to the sub floor. I drove these through the face and only used as many as I needed, since it’s the glue that makes the permanent bond. The holes from driving the nails were filled with a filler that matches the natural colour of the plywood, making it difficult to see them after the floor is finished.

Speaking of finish, here’s what I used: a mix of clear oil based polyurethane with an oil based tinted urethane called “PolyShades”. The colour of the Polyshades is “American Chestnut” and I mixed 1/2 of that one liter can to the full 4 liter can of clear:

I used this same mix before on the red pine floor I installed in my last house and it worked great there. I also used it on the plywood floor in my basement with excellent results. Unfortunately at some point the manufacturer changed the formulation of the clear finish (to use a different solvent, one that is not on the VOC ban list, but no less harmful) and the dry time for the product changed as well. Combined with the infloor heating making the floor warmer than ideal, it was VERY difficult to paint this on and maintain a wet edge. More on that later.

LATER NOTE: I now recommend the Minwax clear oil based poly for floors, as it has a longer dry time which lets you maintain a wet edge. It also doesn’t have the heavy smell that the Varathane product has, making it much more pleasant to work with.

The resulting colour is a very pleasant nut brown with that is not overly dark. It’s important when using a mix like this to get the colour right for the first coat – repainting to darken will produced streaks and appear more uneven:

I used a 3″ brush coating two board widths at a time to try to maintain a wet edge, but it was difficult. It looks pretty good in the photo, but if you look closely you’ll see how it’s slightly darker at the joint of every second board. That ‘s the overlap that a wet edge will prevent:

Given what I know now about this problem, I would have changed what I used. In particular, I would have changed to all water based products just to avoid the mind killing fumes from the solvent based finish. That would have been time consuming to find a colour that I like in a water based stain, since they don’t have the same “wet” look as the oil based ones. Still, I’d settle for a less ideal colour in favour of a more even coverage and more pleasant experience.

How it looks after that first coat. It was a lot easier to keep a wet edge in the smaller area:

The next day, I lightly sanded the floor and gave it the second coat, but this time I used just clear oil based urethane. That second coat did make the colour look A little bit more even.

Two days later, after that second coat had fully dried, I switched to water based satin polyurethane for the final two coats. The overall look is very nice, but you can still easily see the lines every second board where the finish overlapped. Nothing that is noticeable in a furnished room, though, and not really anything that looks bad. The camera actually doesn’t show it exactly as it is – it looks better in person:

A top down closer look. Not many would guess that this is actually plywood:

When that room was complete, I moved out into the hall and currently have just the colour coat and one coat of clear on that. I’ll put the two final coats on after the other floor areas are finished.
When painting this one, I turned off the infloor heating and tried harder to avoid overlaps. The results are not perfect, but certainly a lot better:

After the hall, the master bedroom, and I just finished laying the floor in there at the time of this writing. Next step will be to apply the colour coat and that should turn out much better.
Notice the grain patterning that all but disappears when you paint on the first coat. Of course, a clear finish alone should retain that, but then the floor would be lighter in colour than I want:

I made a detailed video going through the installation and finishing process:

To sum up, I will say that you need to do this for the right reasons – getting a cheaper floor may not make up for the work involved on its own. For me, the fact that it is solidly attached to the sub floor and eliminates raised transitions between floor types (wood and ceramic, for example), make this option well worth the extra time and effort. I also end up with something that is fairly unique and more or less looks exactly the way I want it to.
Also, as good as the final result looks, it’s less precious than an expensive solid wood floor and will likely be treated like a floor should be. After all, it’s only a very recent expectation that floors should be home and garden magazine perfect – most older houses, even the fancy ones, had modest floors.