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Ran D. St. Clair · 11-08-2009, 12:15 PM

I have a crush on foam

My plan for the floor is to put ½” R-MAXX foam board on top of the original wood truck bed, and then ½” plywood on top of that. It’s not as much insulation as the walls or ceiling, but I figure heat rises, so it should be enough to keep the heat in when it is cold out. I suppose it might not be so good for keeping the cold in, like when I am parked over hot pavement or when the generator is running and dumping a lot of hot air under the floor of the truck bed. Then again the floor is 1 ½” of wood, followed by ½” of R-MAXX, Followed by ½” of plywood, and then vinyl flooring. Some of those things aren’t the best insulators, but it all adds up.

I plan to lay down ½” by 2” strips wherever the plywood joins, and also around any openings in the floor, like the safe, or the air inlet registers. I will also lay such a platform under the flooring under the toilet, but for the most part the plywood flooring will float on top of the foam. I figure the foam can crush or deform a bit to accommodate the irregularities in the original truck flooring and give me a relatively flat floor without a lot of filling or sanding.

One concern is whether the foam will stand up to the long term pressure of me and everything else in the truck trying to crush it flat. To alleviate that concern I took a chunk of scrap foam that happened to be about 1 foot square and carefully measured it for thickness with calipers. Now foam is springy and hard to measure so I made 50 or so measurements around the outside edge and put the data in a spreadsheet.

I then placed the foam flat on the kitchen floor with a chunk of ½” plywood about 18” square on top. I then jumped up and down on it for a while, taking care to keep my weight centered on the plywood and foam sandwich. I am sure I could crush the edges of the foam if I were to point load it but I wanted to see if it could handle the distributed load.

I then made another 50 or so measurements around the outside edge of the foam with the calipers and entered the data. It’s not a long term test, but the results are encouraging. After the test the foam was slightly thicker (obviously not) but there was no measurable crushing. The foam does seem to vary in thickness quite a lot just as it comes from the factory though.

I think I can reasonably move forward with my flooring plan.

To be Continued…

11-08-2009, 12:15 PM	#131
Ran D. St. Clair Senior Member Join Date: Apr 2009 Posts: 212	I have a crush on foam My plan for the floor is to put ½” R-MAXX foam board on top of the original wood truck bed, and then ½” plywood on top of that. It’s not as much insulation as the walls or ceiling, but I figure heat rises, so it should be enough to keep the heat in when it is cold out. I suppose it might not be so good for keeping the cold in, like when I am parked over hot pavement or when the generator is running and dumping a lot of hot air under the floor of the truck bed. Then again the floor is 1 ½” of wood, followed by ½” of R-MAXX, Followed by ½” of plywood, and then vinyl flooring. Some of those things aren’t the best insulators, but it all adds up. I plan to lay down ½” by 2” strips wherever the plywood joins, and also around any openings in the floor, like the safe, or the air inlet registers. I will also lay such a platform under the flooring under the toilet, but for the most part the plywood flooring will float on top of the foam. I figure the foam can crush or deform a bit to accommodate the irregularities in the original truck flooring and give me a relatively flat floor without a lot of filling or sanding. One concern is whether the foam will stand up to the long term pressure of me and everything else in the truck trying to crush it flat. To alleviate that concern I took a chunk of scrap foam that happened to be about 1 foot square and carefully measured it for thickness with calipers. Now foam is springy and hard to measure so I made 50 or so measurements around the outside edge and put the data in a spreadsheet. I then placed the foam flat on the kitchen floor with a chunk of ½” plywood about 18” square on top. I then jumped up and down on it for a while, taking care to keep my weight centered on the plywood and foam sandwich. I am sure I could crush the edges of the foam if I were to point load it but I wanted to see if it could handle the distributed load. I then made another 50 or so measurements around the outside edge of the foam with the calipers and entered the data. It’s not a long term test, but the results are encouraging. After the test the foam was slightly thicker (obviously not) but there was no measurable crushing. The foam does seem to vary in thickness quite a lot just as it comes from the factory though. I think I can reasonably move forward with my flooring plan. To be Continued…