I know I'm a newbie here but I've been looking into SIPs (Structural Insulated Panels) for a while. I found a web forum that has a lot of info including a thread on building these at home. Most of the users are interested in house construction, but much of the info would apply to a trailer wall.
http://www.sipweb.com/forum/topic.asp?T ... e=SIP+Talk
I was interested in building a cold weather trailer for winter use. These panels are high R and light weight. There are two types.
The first is a glued system where the wood or other material is bonded to a sheet of foam. This sounds easy but the pressure required is immense. It takes at least 5 psi to get a good bond line so big hydraulic presses are used. A 4 X 8 panel is 4608 sq. in. so you need over 11.5 Tons of force to press the panels.
Of course another way is to vacuum bag the panel. Just suck the air mostly out of the bag and you have most of the 14.7 psi atmospheric pressure doing the pushing. Still it take a big vacuum bag and a pretty strong pump (although a strong shop vac gets about 3psi suction).
I know a guy in Alaska building panels this way with epoxy and using cement blocks to apply pressure.... a fraction of the advertised required pressure. He says it's working so maybe the pressure is not as critical if you use the expensive epoxy instead of the polyurethane cements. I only have his account and no first hand knowledge but he is building a pick up camper this way.
The second type of sip is the polyurethane sip where foam is injected between two panels and expands to fill the void. The polyurethane bonds directly to the panels. These have slightly better r-value. This usually take a very expensive machine to spray the hot foam and maintain the dimensional stability of the panels.
All these panels use 3/4" OSB so they are too heavy for trailer applications.
I have experimented with home building these type panels but by using two part pour polyurethane foam. This is the foam the pour into boat hulls for flotation. The two liquids when mixed expand to about 20-30 times the initial volume.
I first built a frame to hold two 12" X 12" sheets of 5.2 luan. Aligned vertically I poured the foam down into the cavity and allowed it to expand to fill the space. I made it about 2 1/2 inches thick ( R-15). The results were good but since I had nothing holding the faces of the panels the pressure of the foam did push the center of the panel faces out slightly… perhaps 1/8” I'm not sure how much force would be neede to hold the shape but it doesn't see like that much. . The working time on the foam once the two parts are mixed is about 60 seconds so you have to work fast. The form sticks perfectly to other foam so you can pour the cavity in several lifts so the pressure is less.
The completed panel weighed about 2 pounds per square foot. The expanded foam weighs 2-3 lbs. Per Cu. Ft.
I next built a 2 X 2 panels three inches thick. I basically built the walls on a frame and poured foam into the cavity between the “studs”.
The results of all panels so far are good. I cannot pull the luan off the foam without breaking the wood.
My next step is to build a 4 X 8 test panel.
The two part foam is pretty expensive but a good source is:
80 cu. Ft. ( 5 gals each part A and B) is $ 260
I think it may be possible to get a professional panel Mfg. make to special make some 2" luan faced panels if we could get a large enough run...but thats just a guess. They may not be interested and it would be pricey. In the spirit of this group, it would be fun to DIY somehow.
I need to sucessully build a 4 X 8 panel before I can commit to this technology as I and doing it "homebrew". I would like to build a few panels and the destructive test them.
If the pour foam doesn't work I will try the baging technique.
I am out flying but if anyone is interested I could post some pictures of my small test panels when I get home Friday.
Sorry this is so long.