Foam Question

[tdale4]

I'm planning a Truck Camper Foamie build and had a few questions for y'all

I can get the 2" Foamular 150 4x8 sheets at Home Depot, my understanding is that Foamular 150 is 15 PSI strength and it's about $43 a sheet, but I'm wondering if the added cost of the 60 PSI Foamular 600 sheets would be worth it, I think I can get them for around $100 each

I'm planning to use 3 or 4 layers of 6oz Fiberglass and Epoxy to skin the camper inside and out, but some of the videos I have seen make me wonder/worry about delamination, would delamination be less of an issue with the 60PSI foam vs the 15 PSI foam?

Other than sanding the foam or using a dog brush to put in a lot of pin holes, are there any other methods to increase the layer adhesion between the foam and fiberglass?

Apricate and advise or insight y'all have

Thanks,
Tim

[Pmullen503]

I wouldn't worry about it. The foam is there to keep the skins apart and for a stressed skin composite structure. 3 or 4 layers of 6 oz cloth is overkill on a camper. All that will give you is more dent and puncture resistance (and a lot of weight).

I'd suggest you do a test: take some 15 psi foam (1 ft x2 ft is what I'd use) and cover it, both sides with 1,2 and three layers of epoxy/cloth. Let it cure fully (a week or two) and test them for rigidity and dent/puncture resistance. You may decide you need less fiberglass than you think. It will also give you some practice if you've never done epoxy/cloth.

[twisted lines]

Had to look up the 600;
Thanks Wish I could walk in and buy it for that.
Are you building a Yeti Bed

[QueticoBill]

15 psi is over 2000 pdf. I believe even EPS - as low as 10 psi - would work fine.

[tdale4]

I wouldn't worry about it. The foam is there to keep the skins apart and for a stressed skin composite structure. 3 or 4 layers of 6 oz cloth is overkill on a camper. All that will give you is more dent and puncture resistance (and a lot of weight).

I'd suggest you do a test: take some 15 psi foam (1 ft x2 ft is what I'd use) and cover it, both sides with 1,2 and three layers of epoxy/cloth. Let it cure fully (a week or two) and test them for rigidity and dent/puncture resistance. You may decide you need less fiberglass than you think. It will also give you some practice if you've never done epoxy/cloth.

Thats a good idea, I will do some testing

I can get the Foamular 150 and 250 locally and they cost about the same,

My main concern is not so much the strength of the foam, but the lay adhesion and potential for delamination

[tdale4]

Had to look up the 600;
Thanks Wish I could walk in and buy it for that.
Are you building a Yeti Bed

Just planning a build for a truck camper that will go on a Tacoma

[tdale4]

15 psi is over 2000 pdf. I believe even EPS - as low as 10 psi - would work fine.

Agreed, My main concern is not so much the strength of the foam, but the lay adhesion and potential for delamination

I will test out some Foamular 150 and 250 so see if layer adhesion is better for the 25psi foam vs the 15psi foam

[Pmullen503]

Sanding is a must. The hot wired surface of the foam does not give very good adhesion.

Also, the stamped lettering is often recessed enough that it may show through the covering. What I did was to use a hot iron and a wet towel to steam the lettering back to nearly level. Then I sand with 80 grit on a long flat board to make sure everything is level.

You don't have to sand all of the surface away but all the surface has to have scratches. Epoxy (or glue/paint)does not penetrate very far into the foam. You'll never get the kind of adhesion you get on wood. But there's so much surface area you don't need that much.

You will have to add recessed wood for any fasteners (think doors, windows, hinges or any interior things like shelving).

[tdale4]

Sanding is a must. The hot wired surface of the foam does not give very good adhesion.

Also, the stamped lettering is often recessed enough that it may show through the covering. What I did was to use a hot iron and a wet towel to steam the lettering back to nearly level. Then I sand with 80 grit on a long flat board to make sure everything is level.

You don't have to sand all of the surface away but all the surface has to have scratches. Epoxy (or glue/paint)does not penetrate very far into the foam. You'll never get the kind of adhesion you get on wood. But there's so much surface area you don't need that much.

You will have to add recessed wood for any fasteners (think doors, windows, hinges or any interior things like shelving).

Appreciate the advice

I was planning on using wood inserts like you suggest, Originally I was planning on using plywood inserts that would be 2" thick, and epoxy them into the foam, but then I read this may be a bad idea because the rate of expansion on plywood is different from the foam, so it can cause delamination.

Is there a preferred method for installing the wood inserts? Like say use 3/4 inch plywood on the inside of the foam if I am mounting something on the outside of the foam? or would it be better to have the insert on the same side as the item that is being attached?

My thought process is that it might be better for the wood insert to be on the opposite side that way it would be more difficult for it to pull away from the foam like might happen if it was on the same side as the fastener.

Maybe I'm overthinking all of this, but just wondering if there is a consensus on the best way to install a wooden insert

[Pmullen503]

Lots of ways to add hardpoints foam. When I did uprights to carry the load of roof racks down to the frame I made "I" beams. 1/2" ply faces with a solid wood core. The faces were about an inch wider than the wood core and channels were routed in the foam to accommodate. This helped maintain alignment mostly, but does give a little more glueing area as well. If practical, a full depth insert is stronger, especially "flanged" as described above.

Foam does have a higher thermal expansion coefficient than plywood but not so much than you have to worry about delamination. Plywood and Epoxy/glass are pretty close so no worries there.

With PMF (canvas) the foam to wood joints on my trailer were visible after a couple years but after a decade of living outdoors, there isn't significant delamination. I would expect epoxy/glass to do better.

Epoxy/glass over foam is used for boats and aircraft which have MUCH higher loads than a trailer or camper. The forces just aren't that great. If you plan to do a lot of off road travel you should design to resist racking: strong corners and bulkheads or gussets to spread out the loads.

BTW, you'll have a much easier time with fiberglass if you radius all your external corners. Glass doesn't like to wrap around sharp corners. For 6 oz cloth I'd shoot for a radius of 1/2" on your external corners. If you are careful (and vigilant during the cure) you can get away with 1/4" radius without too much trouble.