Interior Prep and Subfloor

My ProMaster was owned by a rental company for just over one year. So while in good condition, its use as a rental vehicle left it a little scratched up on the inside. Knowing that condensation and rust can be a problem, I wanted to start by eliminating concern over the scratches lining the floor and wall. So objective #1 before doing any build was to do some light sanding of those areas and repaint it with white, rust-resistant paint. Objective #2 was to lay some beams and insulation on the floor. And Objective #3 was to cut out and lay the actual subfloor.

I'm still refining my process for doing things right (better) and there's a lot of give and take (mistakes), so I'll be sure to expand on those below.

Supplies Used

• Cordless screwdriver, bits, and wood screws
• Cordless jigsaw with wood blades
• Caulking gun
• Utility knife
• Brown construction/builders paper roll
• Blue painters tape
• Respirator mask, eye protection, and gloves
• 3 cans of white paint-primer
• 80 grit sanding sponge
• 5 strips of 2x2", 8' pine
• 1 strip of 2x2", 8' cedar
• 1 can of construction adhesive
• 2 sheets of 1 inch, 4x8' polyisocyanurate (polyiso) insulation
• 1 roll of 10x12' moisture barrier material
• 1 can of adhesive spray
• 4 (originally got 2 - see below for mistakes made) sheets of 19/32", 4x8' OSB (type of plywood)
• 2 cans of Great Stuff Gaps & Cracks insulation foam

Cutting Floor Templates

While I needed to prep the van for laying insulation and a subfloor, I also wanted to be efficient with my Satuday. So I first started by creating subfloor templates to cut my OSB plywood while the repainted scratches dried. Using a roll of construction paper lined up against the wall, I cut out portions where the wheel wells and other irregularities impacted a straight line. This turned out to be difficult on two fronts: 1) Wind coming through the side door was annoying when dealing with paper. Who would have thought? So I closed the door. It wasn't a difficult problem to solve. 2) Simply put, the irregularities are really hard to cut out properly. So I had some bad lines... but nothing extra paper and painters tape couldn't solve.

You can see in the video and pictures a little bit of this process and making fixes. The moral or the story for me was to go slowly next time and cut sections out incrementally. Also, tape and extra paper are your friends and work great to fix the little (big) mistakes.

Sanding And Painting Interior

After finishing my templates, I got to work sweeping and cleaning up the inside of the van. I watched a lot of people remove rust and repaint the areas to protect it going forward, but I didn't really have rust so I wasn't planning on doing anything. Then I saw Into the Mystery do some sanding and repainting inside one of his conversions and it made sense to take the extra step to protect small scratches against developing rust.

80 grit sanding sponge in hand, I got to work on the floor and portions of the wall that needed it. The sponge made quick work of things and within 30 minutes I'd sanded areas with scratches and exposed the metal. It was way easier than I anticipated. I also had to use a T-40 socket bit to take off the tie-downs that were screwed into the hull interior too. There were 8 in total, but one by the sliding door had been stripped and couldn't be removed. After sweeping again and washing down the floor and walls with warm water, I let it dry for 10 minutes and got to painting.

Originally I bought one can of Rust-Oleum paint-primer, thinking that would cover the surfaces needed. That ended up being false as I coated it thickly and ran out 2/3 of the way through. I also wanted to do a second coat, so I quickly went to the True Value hardware store down the street and picked up two more cans. Using all three cans, I was able to finish covering most of the floor and patches on the walls with two coats. I let it dry for just over an hour while I cut the floor, but I should have waited longer before laying down the support beams, which I'll highlight below.

Cutting Subfloor OSB

While letting the paint dry, I put my template for the driver side on my full size 4x8' OSB, traced out the lines with a permanent black marker, and made my first cut. It was very exciting. It was even more exciting after finishing those cuts to realize it actually fit well, with very little gap where it met the wall. So then it was on to the passenger side piece...

I'll note here that I had originally pegged the rough measurements of the floor under 6' wide and 10' long. So with a confident heart, I walked into Home Depot and bought two 4x8' OSB pieces and had one cut in half lengthwise. I figured 4x8' + 2x8' will cover my back portion width and then I'll have another 2x8' section for the remaining 2x6' top portion of the floor... But, as it turns out, a rough measurement and willing heart don't quite cut it.

I traced my template for the passenger side and used the jigsaw to make my cuts. But when I put it in the van, there was a little over an inch gap between the left and ride side pieces. This was because I was cutting off small portions and, again, because I didn't measure properly. That's when I also realized my other 2x8' piece wasn't wide enough for the top portion either. Clearly, measuring is a weakness of mine I need to immediately correct. 

So I needed to get two more 4x8' pieces of OSB for both the passenger side back and the top section. Because it was getting later in the day though and there were other base level things to accomplish, I left that task for Sunday morning and moved on to the insulation and floor beams. The next morning I went to Home Depot, got my OSB, made more accurate measurements for both the passenger side and top (using a new paper template), and made the cuts. This time I was more conservative and figured I could sand down areas that weren't fitting into place, which turned out to be a great way to get a perfectly snug fit for all three pieces.

Subfloor Beams, Insulation, and Moisture Barrier... Putting It All Together

Since I needed to lay the beams underneath my OSB floor anyway, I started working on those Saturday as the wrap up to my first full day on the job. I wanted something to screw my OSB floor into, but again wanted to avoid drilling holes in the hull of the van. I saw how Nate Murphy glued down some wood to the floor of his Transit and decided to go that route. I took four pieces of 2x2" pine and spaced them out in the grooves of the floor and cut a piece off the fifth 2x2" to secure at the front, perpendicular to the rest. Using some Gorilla Glue construction adhesive, my brother helped me drizzle it on the straightest side of the first piece and pressed down for a minute to hold it in place.

At first, it didn't end up having a firm hold because of the fresh paint, the slight curve to the wood, and because we didn't use enough glue. So we ended up being overly generous with the glue and pressed down firmly for a few minutes on each beam (in some instances we employed some kettle bells for weight). The extra glue and minutes applying pressure helped them not pop off the floor where they slightly curved. Knowing they would cure over the next 24 hours, I felt more confident in the probable end result.

Using the OSB cuts I'd made as a guide, paired with better measurement, I started to cut the shapes out of my polyiso foam insulation to fit between the beams on the floor. I used my permanent marker to trace the lines and used the jigsaw to cut them. I heard you could cut polyiso with a utility knife and then snap off the undesired pieces. But for the 1" board, a standard utility knife blade wasn't long enough to go all the way through and trying to "break off" the cut pieces resulted in bad lines. You'd be able to cut the 1/2" polyiso with a utility knife without a problem, but for this I used the jigsaw. It was messy since it caused little pieces of polyiso to get everywhere, but it did cut through it like hot butter. Additionally, minor adjustments were 100% easier and more precise with the jigsaw since you didn't have to muscle your way through the cuts. With all my polyiso pieces cut and ready for permanent placement, it was time to call it a night on Saturday.

On Sunday, when I went to Home Depot for the additional OSB, I also picked up a 8' cedar 2x2" piece of wood to trim the side door step and back doors. At the side door, I glued the cedar down and clamped it, which helped secure it better than my own weight. I didn't glue the cedar piece by the back doors and planned to leave it floating since the OSB floor would screw into it anyway.

So with all my beams in place, polyiso on the floor, and subfloor OSB pieces cut, I was ready to pull it all together. To fill the cracks on the floor and have "complete" insulation, I used Great Stuff Gaps and Cracks expanding insulation foam. Someone recommended getting the pro version and a pro gun since it was difficult to deal with, but I found the standard version to be pretty controllable, especially once you got a hang for how it came out of the nozzle. I didn't worry about spillover since I'd watched a video where someone easily removed extra foam with a flexible hacksaw blade. So I sprayed liberally and made sure to fill every gap, letting the foam expand onto the surface of the floor. I even used the foam to build up areas of the polyiso that weren't as high as other areas due to the ridges in the van floor.

With the foam curing for the next few hours, my brother and I got a quick smoke in... cooking a full chicken and 2 slabs of ribs in his smoker. Sorry, no pics. But it was delicious.

Toward the end of the evening, the foam was hard enough to justify putting the OSB flooring down and screwing it into place. So I used the hacksaw to remove the extra foam. It took maybe 30-45 minutes to cut away all the extra foam around the outer edges, the four main beams, and the two trim areas with the cedar wood. On the back trim, where I didn't glue the cedar, the Great Stuff foam actually worked as an adhesive and secured it in place. So that was an added benefit and I think you could use the foam as a supporting adhesive if you wanted.

(I'll stop here for a moment to say that I was going back and forth about having a moisture barrier between the insulation and my subfloor. After "completing" the floor Sunday, I decided during the week to put the moisture barrier in place because I didn't feel like my insulation was as gap-proof as I'd originally envisioned. So I ended up pulling up the OSB and putting a MoistureBarricade layer underneath before securing the floor to the beams again. I simply cut the film to the shape of the floor and then glued it to the floor using 3M High-Strength 90 spray adhesive.)

With insulation and a moisture barrier in place, it was time to secure everything down. I put the two back pieces in and started screwing them into the beams at the front, working my way all the way back to the cedar trim by the back doors. I left the top OSB piece off so I could see where the four 2x2" beams were lined up and I used a ruler mark where I needed to screw down the subfloor. The two back pieces intentionally met atop one of the beams in the middle so I could secure them together in a sturdy position. The 2x2" pine isn't exactly 2 inches wide, so it's about the thinnest I would go trying to screw together two joining pieces of wood. I wasn't terribly concerned about splitting the wood, but tested it out with scraps just to be sure and it proved to be safe. For the beam where the two met, I alternated the screws about every 8-10" between the two boards.

With my two back pieces screwed down, I put the top board into place, secured it to the 4 main beams, front beam, and cedar trim at the side door, and then I had a subfloor. Dan (aforementioned brother) was super thrilled for me. Aren't you?!