Ballroom Dance Deck

My wife and I are ballroom dancers, and fond of lessons and dances at the Regent. Then COVID-19 hit, and it seemed like an end to the hobby. Fortunately, the Regent Ballroom started lessons and dances via Zoom. Just one problem: our downstairs was all carpet. We had planned to have hardwood floors installed in the spring, but with COVID-19, that was no longer an option.

So after the first night of dancing on carpet, Amy said to me "We're going to be doing this for a while." We looked at buying a portable dance floor, but reviews said it was like dancing on plastic. So we designed our own 12'x8' floor using three sheets of plywood. Plywood is NOT a first choice for flooring, but people report success using it. We figure the floor only has to last a year.

First step was blocking out a floor plan in our living room.:

The little ⊗ symbols mark screw locations. More about that later.

The computer area is where I work from home, so now I work from a ballroom. The fridge in the living room is an accident of timing. While our kitchen was being remodeled in late 2019, we did all our food prep and eating in the living room, and cleaned dishes in the laundry room sink. We planned to take advantage of a program where the electric company would pay us to haul off the 1994 vintage fridge, but when the epidemic struck, minimizing grocery trips became important, so we kept the fridge.

The parts list came in at about $350, including $65 to have the lumber delivered. 4'x8' sheets of plywood do not fit in a Prius V. We chose "HPVA" pre-sanded maple plywood. I'm pretty sure designer plywood is not recommended for flooring, but hopefully it will last a year until we can get a real hardwood floor installed, and provides a nice smooth surface.

During construction, we continued to dance in the playroom, with red masking tape marking a 12'x8' area equivalent to our future dance floor.

First step was finishing the boards. To keep the boards clean, we put them over 8' "2x2" furring strips that we ordered with the boards. We used a clear satin water-based polyurethane coating for floors, applying two coats on the bottom of each board and four coats to the tops. After the first coat, there was the expected "grain raise" effect, so we sanded with #150 sandpaper before the second coat. Before the last top coat, we sanded with #150 and #220 sandpaper, vacuumed, and wiped down with tack cloth.

Next we cut the rug, using a box knife on the old thick wall-to-wall carpeting that came with the house in 1994. The red line going under Amy's knee is red yarn that we strung like a chalk line between two small nails hammered into corners of the future floor.

Carpet was easy to rollback after cutting. Underneath was a foam pad -- we pulled lots of staples holding it to the subfloor.

We brought the finished boards in from the garage and laid them out. Worried about cutting too big a hole in the carpet, we had been conservative in cutting and found that we needed to recut around the boards. This time we used sewing scissors, a wedding present from my Aunt Clotilde, an expert sewing author, who's probably rolling in her grave that we used the scissors on carpet. In our defense, we have never committed the sin of using them to cut paper.

Our 36 year old subfloor was less than perfectly flat, and buckled in places because the house builders evidently did not sufficiently "gap the boards". We put the finished plywood aside, and remediated the problem as best we could by retroactively cutting some gaps between boards with an oscillating saw, replacing some of the nails to joists with deck screws, and sanding.

We also painted the subfloor with KILZ primer to protect it from spilled water. We didn't have enough to cover the entire subfloor, so we skipped parts that would be under centers of our finished plywood sheets.

The original plan called for 6 screws on each side of a seam, on 16" centers, same as the joists. But later flooring information I found indicated that the top floor should not be screwed to the joists, hence the design switched to using 7 relatively short screws on on each side of a seam, on 15" spacing that misses existing subfloor nails. Given the non-flat subfloor, we ended up not just screwing down seams, but all long edges the centerline of each board, for a total 21 screws for the middle board, and close to that for the north and south boards.

Using a counter-sink drill bit, we drilled holes through the boards into the subfloor and screwed them down to the subfloor with #8 1-1/4" stainless steel wood screws. We used stainless steel since the smallest box of screws had more than enough no matter what material, so might as well go with the best, and the leftovers can be used for just about any application.

Here is the finished floor. It was too smooth on first go. We were able to restore traction by putting down rosin for Amy's violin. Lessons and dances are delivered via Zoom on the Macbook Air, hooked to the TV.

Hustle works much better on finished plywood than carpet. Now we're learning how do a "12x8 waltz". Spin-turn, reverse-twinkle, chasse, reverse-twinkle, fall-away, ....