How to Install a Plywood Shop Floor

Article - October 8, 2013

Please enjoy this guest post from Dave Frameli documenting his experience installing a plywood floor in his shop. —Marc

I built a 900sf wood shop on the back of a two car garage and I wanted a wood floor for a couple of reasons. First it’s easier on the body after standing all day and second, and just as important, was the insulation value. I wanted to keep my utility bills to a minimum so along with insulated 2X6 walls, 5/8” drywall and R43 insulation in the ceiling, I wanted an insulated floor. I did some research on-line but most of my plan came from what I read in books.

Getting Started

The first thing I did was fill in the cracks between the block foundation and the floor. My thought was to stop any moisture from getting to the floor and baseboard. I choose a polyurethane caulking made especially for concrete and masonry.

Securing the Lumber

To secure the 2x4s to the concrete I planned to shoot nails with .22 blanks. The first gun I tried wouldn’t drive the nails deep enough so I exchanged it for a gun that could handle a higher caliber blank. I tried this gun and the nail still didn’t go far enough in but this time it actually cracked my concrete. So within just a few hours I was on plan “C”, using Tapcon screws. I wasn’t looking forward to all the drilling but I wanted to secure the floor to eliminate any movement. If the wood floor gets taken out in the future, it will not be hard to fill the holes and cover the floor with an epoxy.

1I started securing pressure treated 2X4’s along the entire perimeter. I ran a good sized bead of decking glue under the 2X4s and smeared the glue as I pressed the boards into position. I used an impact drill along with the bits that came with the Tapcon screws to drill through the lumber and into the concrete.

After the perimeter was complete, it was time to mark where I wanted the 4X8 sheets to lay. Every article I read said it was better to install the 2x4s on 24” centers but I didn’t feel this would be strong enough for all the heavy equipment in the shop so I installed the center boards on 16” centers. I’m glad I did. Everything I read also showed the plywood laying parallel with the 2X4s. I ran this through my head while looking at the floor and there seemed to be a better way. When the plywood lays parallel with the lumber, each sheet is supported by four lengths of 2X4s. If I laid the plywood across the 2X4s there would be seven lengths of 2X4s supporting each 4X8 sheet. So I experimented and laid out two sheets of plywood, one in each direction and sure enough there was a distinct difference in support.

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Foam Insulation

I started cutting the foam boards on a table saw but it really made a mess with foam dust flying all around so I ended up using a jig saw instead. For every 4X8 sheet of foam board there was a 10-11” piece left over. I used the small scraps as a temporary walkway making it safer and easier on the ankles when carrying sheets of plywood into the shop. The leftovers then went into the attic.

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Vapor Barrier

9There’s not much to installing the plastic vapor barrier. I used 6 mil clear plastic from a 100’ roll. Once I laid it out I randomly stapled so it wouldn’t move when I walked on it. I did overlap the next sheet at least 6 inches and I taped the seams with some leftover Tyvek tape but any seal type tape will work. Note: Before you start laying the plywood down, inspect the plastic for small holes made from accidentally walking over the edge. It’s an easy fix, just cover the holes with tape.

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Plywood Flooring

7My initial plan was to use tongue and groove (T&G) plywood to ensure the edges would always remain level with each other even if some boards started to warp. The biggest drawback for the T&G was knowing the shop will go through many changes over the years and if I used T&G I would lose the option of pulling up sections of plywood to run wiring under the floor. I also had thought if a section of floor ever gets damaged and had to be replaced, what a chore that would be to repair it! I’m sure this floor will get damaged at some point along the way. I chose to use 23/32″ sanded plywood sheets that were not T&G. Note: Remember to stagger the plywood; it will make for a much stronger floor overall.

Securing the Plywood

10I used 2” Green exterior screws with T-20 star drive heads to secure the plywood to the 2X4s. Whatever screws you use make sure they can be used with treated lumber. Initially I made a story pole from scrap wood so I would know where to align my screws but I found the fastest way was to use a 4’ rule. Lay it down across the board and seat the screws into the plywood with a hammer about 1-1/4” from the edges and then every 16”.

Note: Do not screw in the corners until the next row has been installed. This helps prevent the corner edge from smashing outward which prevents the next row from having that perfect fit.
For driving the screws in, I didn’t set my drill clutch to leave the screws level with the surface of the floor because I wanted to drive the screws below the surface. This way I would feel comfortable sitting a wood project on the floor or even sliding it without gouging the project.

Finishing the Floor

11Overall the hardest decision was how to finish the floor. Initially I planned on putting down an epoxy but I couldn’t find one that could be used on wood. Then I planned on using a solid stain looking at colors from light green to gray. For these I stained some wood scraps and walked on them for a few days only to discover it would be too hard to sweep and keep clean. In the end I decided to lay down three coats of floor polyurethane.

12I just poured it directly from the can to the floor and I used a 10” 100% lambskin applicator to apply the finish. Between coats keep I kept the applicator on the stick and just wrapped the applicator in a few small plastic bags to keep it from drying. I only sanded after the second coat because I didn’t want the floor to be too slippery. Also using a clear finish showed all the marks in the plywood and even the paint showed along the edges so overall it gives the shop more character.

This project took longer than I expected but much of this was trying things out for the first time and rechecking it as I went along. I didn’t count the hours but I spent no more than (3) weekends and an hour or so each weekday to get it all completed including finish. After about 6 months of making saw dust I am no longer a concerned about the floor being slippery. Also with the finish on it, it is really easy to sweep up.

I hope this makes things easier if you’re deciding if you want to install your own plywood floor. OH, BY THE WAY, MY WIFE HELPED!

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