Strong and light. Hybrid cabinet construction thoughts.

[dbhost]

I am not sure how many here are interested in, or follow the DIY RV / Camper build crowd, but they have a technique that looks interesting that might work for my camper van cabinet rebuild project...

They use lumber framing, typically 3/4 plywood and inset 3/4 or whatever size they wish to work with, XPS foam board, coated with Titebond II, and wrapped in typically recycled bedsheets or canvas depending on the builders whims. This is known as PMF, or Poor Mans Fiberglass.

While I would not use it for any surfaces facing the user I.E. visible parts of the cabinet with doors etc... closed, I could easily do this for things like dividers, and, well any bits that can be then veneered.

The idea is the PMF build is radically lighter than a traditional all wood build. The drawbacks are you have to insure anywhere you want a screw to hold securely BETTER be where the wood is, bits of foam get everywhere while you are working with it, and you pretty much MUST paint or veneer it...

Since my camper van is a 3/4 ton and not a 1 ton, I am wanting to be careful with weight, especially since I am replacing the missing 10 gallon water tank with a 20 gallon unit, and if I can find space, a 10 gallon wastewater tank. Since fresh and waste are never full at the same time, lets assume between the drinking water tank, and the toilet fresh water which has its own supply are full, that is 25 gallons of water, so roughly 200lbs of water I will be carrying, plus cast iron cookware, and a privy tent since the camper is too small to have its own internal shower... and... well it all adds up.

I am not sold on this idea yet, but definately pondering it, along with the idea of Poplar Ply and pine bead board construction with a stain finish and epoxy sealed to make the shine pop and protect for potential water intrusion.

I think Prefer the look of actual wood, but I like the light weight of PMF.

Have any of you taken on a project like this? If so how did you approach it?

[capncarl]

Instead of Titebond why not go ahead and use fiberglass (polyester) resin? No more than you will use the higher price of polyester resin will not be significant. It’s a lots easier to use like this because of its fast cure time. Any weight you save is valuable.

[dbhost]

Polyester resin eats XPS foam like Cookie monster goes through Oreos... However Epoxy resin is fine, and a consideration since Epoxy resin isn't horrid...

[mpc]

PMF is new to me. But another way to make a strong sheet panel is to sandwich foam core with thin plywood on both sides. Similar to how hollow-core doors are formed with thin panels sandwiching corrugated spacer stuff. A band of real wood along the edges of the foam core also sandwiched by the plywood layers (again similar to hollow core doors) gives screws, tenons, etc. something solid to bite into. My gut feeling is that such panels would be not much heavier than PMF but would be easier to build, less messy to build, and would not require yet another layer of veneer to have a nice appearing surface.

Small metal "L" brackets inside the cabinets, reinforcing the corner joints, add next to no weight but do add a lot of strength. Since most pickups do not have rigid frames - especially in torsion - some "flex" in furnishings is probably advisable so they don't get torqued apart. Screw joints, compared to mortise and tenon joinery, allow a little flex. Larger than normal gaps between cabinet doors, sloppier drawer fitting, etc. let the main cabinet flex/twist with the truck while preventing doors from jamming into each other, drawers from binding, etc. Look at pickup bodies: there is a fairly large gap between the "cab" portion and the front of the "bed" portion. That gap exists so the cab and bed don't crunch into each other when the frame twists (in torsion) or bends (like a banana).

mpc

edit: Some light aircraft are built using thin plywood over foam core with wood ribs assuring proper airfoil shapes. Some aircraft, and many large model aircraft, use traditional fiberglass over a foam core. The core provides the basic shape when "laying up" the fiberglass and adds some overall strength. It is cut with a "hot wire" gizmo:a stiff 3-sided frame with the 4th side being a wire carrying a low voltage but high amperage current (adjustable) so the wire gets warm but not red-hot; this buzzes through blue foam core material like a hot knife through butter and allows for airfoil shapes to be cut on a tapered wing. Not too difficult; I did this decades ago. Sanding the outer fiberglass surface to be aircraft-smooth took the most time. The result was a lightweight wing panel, fairly stiff, and pretty strong. But not as strong as a typical kitchen cabinet - leaning on the wing could snap it.

[cwsmith]

Is this something you buy or you have to fabrication material you have to construct yourself?

I searched for PMF on the internet and only could find political or organizational references as in Professonal Management Foundation... obviously not the correct reference.

Not know exactly what it is, it seems like a lot of messy work. Not knowing exactly what you are trying to build, I think my approach would be to either make any cabinets out of pine, and reinforcing any areas that might be stressed with framing stock. Of course I don't know what you are striving for, as far as look and style is concerned.

What I do know, is that working with fabrication materials like fiberglass, graphite, etc. is laborious and smelly, often requires the building of mold (a pain for singular one-off projects.

CWS

[capncarl]

I don’t think there are any molds in PMF, just stretching some fabric tight and smearing some Titebond on it to saturate it and stiffen it when it finally dries. I suggested fiberglass resin because it dries in minutes rather than days. Neither sounds like a good option. I’d suggest 16 gauge aluminum sheet metal and a cheap harbor freight sheet meal break and a sack of rivets first!

[capncarl]

DB, had you considered building some parts of the cabinets out of metal? Everything doesn’t have to be wood. You can still use wood doors, shelves, the frames can be wood.

[dbhost]

For those interested in PMF, the forum talking about it mostly is Teardrops and Tiny Travel Trailers (tnttt.com) as it is mostly used in the DIY camper community, although there are folks that use it for DIY boats as well...