I'm starting the design process for a small truck camper, and I'm considering using a plywood/foam composite panel for the structure. I've found a lot of build threads using this method, but not a lot of info on constructing the panels or how to epoxy the structure together. Is there a thread detailing the process that I am missing? Thanks
Foam composite panel construction techniques?
- Thread starter ToyoTitus
- Start date
You should look at the Foamies section at tnttt.com/
rruff
Explorer
It's my understanding that you can't rely on foam alone in the cavity unless it is foam that is designed specifically for this. And that foam is $$$.
I've built and am about to build a camper using panels with wood stringers spaced ~1ft apart in addition to hardware store extruded polystyrene. Marine plywood for the exterior skins. PL Premium seems to work well for the foam and wood both. The foam needs to be scuffed up first to get a good bond.
rruff
Explorer
I've done some more investigating and the heavier XPS foam should be strong enough for this application, so long as you don't expect too much from it. Like Foamular 600 or 1000. Or Dow Highload 60 or 100. I haven't found a source for heavy Foamular unless you buy huge quanities, but this place sells Dow Highload. Should cost ~$40 for a 2"x2'x8' sheet. http://www.whitecap.com/shop/Search...&pageView:grid&minPrice:&maxPrice:&pageSize:&
ski_bike_camp
Ski_Bike_Camp
I am part way through the process. You need to use a structural foam like Corecell or Divynicell. 
rruff
Explorer
There is at least one place making foam and fiberglass structural sandwich using Dow XPS foam. http://www.styromax.com.au/category/products/#styromax-panels
Silverado08
Observer
Looks like great product,,too bad its too far away to shop,,for me anyway,,
is there any dealer in NA selling these panels?
Thnx
Victorian
Approved Vendor : Total Composites
We are in Victoria. On vacation right now but back in the office on Thursday.
goatherder
no trepidation
Making your own panels is easy. You do need to scuff the foam boards for good bond. I'd use a sanding block w/ 60 grit. You can get some epoxy off Ebay or from a composites supplier like Rev-Chem. These guys have a house-brand glue that is reasonably priced. You don't need to pay boat store prices for West System. You want a medium hardener, not fast or slow. You also need a thickener like colloidal silica, and some microballoons. The supplier will set you up.
I'd sand the foam sheet, then vacuum out all the dust. Lay the foam sheet and your plywood down on a flat shop floor on some plastic sheeting. Mix up some epoxy, I'd start with a pint. Using a small paint roller, I'd roll pure epoxy onto the plywood. Let that soak in for a while. This "primes" the wood and keeps it from sucking all the glue out of the joint when you mate it with the foam.
Then I'd mix a little silica into the rest of the pint, and start adding microballoons. Don't breathe these. Add microballoons until you get a mayonnaise-like consistency, then spread it all over the foam using a notch-trowel. (like you would for carpet glue)
Then flip the plywood over onto the foam, lay some plastic sheeting over it, and lay a piece of 3/4" plywood on top of that to evenly compress the sandwich. You could add more lumber and weight if desired; it's important to weight it evenly. After cure, flip it over and do the other side.
FYI - epoxy doesn't stick to plastic sheet, clear packing tape, or grey duct tape. These can be used as release materials. Microballoons are NOT to be used in a structural bond, but when bonding to foam they make the epoxy go further and the glue mix is still far stronger than the foam it's bonding to.
Panels can be connected using fiberglass tapes. These can be made by wetting out 2 or 3 plies of fiberglass cloth between two layers of plastic; squeegee the glue around until the cloth weave disappears. Then cut strips on a 45 degree angle. Peel off one side of plastic, apply the tape to the joint, squeegee all the air out and then peel off the outer layer of plastic. Outside corners need to be radiused, inside corners need a fillet of epoxy thickened with silica to a peanut-butter consistency laid into the corner before the cloth tape is applied. Smooth the fillet with a tongue depressor for consistency, apply the tape, squeegee out the air. You can wait until after cure to remove the outside plastic from the tape.
I'd sand the foam sheet, then vacuum out all the dust. Lay the foam sheet and your plywood down on a flat shop floor on some plastic sheeting. Mix up some epoxy, I'd start with a pint. Using a small paint roller, I'd roll pure epoxy onto the plywood. Let that soak in for a while. This "primes" the wood and keeps it from sucking all the glue out of the joint when you mate it with the foam.
Then I'd mix a little silica into the rest of the pint, and start adding microballoons. Don't breathe these. Add microballoons until you get a mayonnaise-like consistency, then spread it all over the foam using a notch-trowel. (like you would for carpet glue)
Then flip the plywood over onto the foam, lay some plastic sheeting over it, and lay a piece of 3/4" plywood on top of that to evenly compress the sandwich. You could add more lumber and weight if desired; it's important to weight it evenly. After cure, flip it over and do the other side.
FYI - epoxy doesn't stick to plastic sheet, clear packing tape, or grey duct tape. These can be used as release materials. Microballoons are NOT to be used in a structural bond, but when bonding to foam they make the epoxy go further and the glue mix is still far stronger than the foam it's bonding to.
Panels can be connected using fiberglass tapes. These can be made by wetting out 2 or 3 plies of fiberglass cloth between two layers of plastic; squeegee the glue around until the cloth weave disappears. Then cut strips on a 45 degree angle. Peel off one side of plastic, apply the tape to the joint, squeegee all the air out and then peel off the outer layer of plastic. Outside corners need to be radiused, inside corners need a fillet of epoxy thickened with silica to a peanut-butter consistency laid into the corner before the cloth tape is applied. Smooth the fillet with a tongue depressor for consistency, apply the tape, squeegee out the air. You can wait until after cure to remove the outside plastic from the tape.
fluffyprinceton
Adventurer
Excellent write up! One minor quibble...
"You want a medium hardener, not fast or slow" In hot temps you want slow & in cold temps you want fast.
If you want a "skin stressed structural composite sandwich" http://www.oneoceankayaks.com/Sandcore.htmthe foam needs to have the structural ability to transfer the loads to the skins. Structural foam or balsa in not cheap...You absolutely CAN make "a skin stressed structural composite sandwich" using the method described so well by goatherder - just keep in mind it will be heavier than vacume bonded panels - because without using vacume bonding it takes lots more epoxy to bond to the core material & you'd better make the skins thicker to compensate for the less than optimum bonding pressure. Still going to be the lightest for a given strength of all the DIY building methods.
Most DIY builds use a hybrid composite that rely on a seat of the pants combination of foam, internal framing & structural of non-structural skins. The tnttt.com/ is full of these & they seem to work although if you come from a boat or airplane background you'll be shocked at what they are doing...Moe
"You want a medium hardener, not fast or slow" In hot temps you want slow & in cold temps you want fast.
If you want a "skin stressed structural composite sandwich" http://www.oneoceankayaks.com/Sandcore.htmthe foam needs to have the structural ability to transfer the loads to the skins. Structural foam or balsa in not cheap...You absolutely CAN make "a skin stressed structural composite sandwich" using the method described so well by goatherder - just keep in mind it will be heavier than vacume bonded panels - because without using vacume bonding it takes lots more epoxy to bond to the core material & you'd better make the skins thicker to compensate for the less than optimum bonding pressure. Still going to be the lightest for a given strength of all the DIY building methods.
Most DIY builds use a hybrid composite that rely on a seat of the pants combination of foam, internal framing & structural of non-structural skins. The tnttt.com/ is full of these & they seem to work although if you come from a boat or airplane background you'll be shocked at what they are doing...Moe
offroadkiwi
New member
One approach is to make your light wooden frame with studs/stringers, exactly the same wall thickness dimension as your foam thickness that you decide to go with.
Using epoxy glue and screws, cover the light frame with ply, then fit & glue in foam panels from the inside, then line inside of the structure with thin ply. Thereby making a composite panel in situ. Ply can be attached with any method(screws is best) but it's fairly academic if using epoxy glue, as it is generally stronger than the wood itself. (In some boat construction, glueing 2 plys together, you remove the screws after the glue sets up)
Epoxy is good for the foam too (at least I understand so, I haven't personally used it in foam, but I'm told by another boat builder it was his preferred glue for polystyrene to plywood, and is also it's the duck's nuts for an exterior covering of (Say) 6 oz fibreglass cloth (2 coats, 3 if you want mirror finish).
Doing it this way might be slower than pre-fabbing the panels, but could be less demanding over-all. It also has the immense advantage of an all-in-one build not relying on contact adhesive for corner joins. Wiring can be sorted before the interior lining goes on, so it gives a higher degree of flexibility during the build process with less forward planning required.
I'm considering this approach for a 5-6 ton expedition truck camper, and after building a wooden aeroplane and boats, I can't see many issues. A quick interior coat of epoxy (with no fibreglass cloth) on the ply would also seal off any formaldehyde fumes, and can be just left like that or painted after a light sand and wipe down with methylated spirits on a rag. (wear a mask for all sanding, especially epoxy where there's cloth)
As an aside, the most common problem I see since I have been watching others projects, is where the bottom wall plate is positioned back from the outside wall of the trailer chassis. By keeping the outside edge of the bottom plate in perfect alignment with the outside edge of the trailer frame, you extend the wall ply down past the bottom plate glueing it (also) to the outside of the trailer chassis. (scuff the metal in that area back to bare steel first, the epoxy glue join will stop it rusting).
Water doesn't like going uphill much in my experience, but most rivers are testimony to the fact that it moves freely sideways, however.
Sitting a wall's bottom plate in from the edge on top of the trailer chassis, and expecting moisture that lands on top of the chassis frame, not to move sideways into the wall, based only on sealant, is not a smart idea, and liable to leak eventually.
If you want to keep costs down a little you could waterproof the exterior ply using painters canvas drop cloths in the system know as "poor man's fibreglass", it works well, however for an overland vehicle or 4x4 teardrop camper that will get a very hard time, the fibreglass is an option that offers more rigidity to the walls than PMF.
It can be achieved, but my advice is to steer away from paint only finishes on ply, as ply contracts and expands.., some oil type stains can work, but paint tends to crack and weather on ply...attached fabric helps keep the paint from cracking.
Please feel free to comment, this is just my view... I'm no expert. I made a mistake in '76, must be due to make another....
