Fiberglass Application for a Truck Camper

I realize I'm a little out of place as a landlubber in a boat-building forum, but I'm looking for help with a fiberglass job and no-body knows glass better than you boat builders.

The project is fiberglassing over an ultralight 1/4 plywood skinned, wooden framed slide-in truck camper I'm building. The goal of the glass is primarily for waterproofing and secondly for minimal structural strengthening (using a single layer of 10oz plain weave).

I'd like to keep a natural wood finish and so will not be painting this camper.

My question is, being as this is not a submerged shell, would Polyester resin be an alright choice for my application? Epoxy is more expensive, more affected by UV (more of an issue in my case vs a boat hull), but offers better adhesion to the plywood (supposedly), better strength, and is a little easier to work with in my limited experience.

UV degradation is a big concern for my application, if I use Epoxy I'd use a spar varnish to finish. Not sure what to use over a Polyester though but would imagine it would hold up better to UV?

All help, tips, advice appreciated. Thanks

 

My brother and I made a small plywood and lumber cap for a small Toyota or Datsun quarter ton pickup back in the early 1980s. I think we just painted it. We entually sold it after selling the truck a few years later, but we hit a few regattas with it towing our boats behind it.

The paint provided some protection, but a few more coats might have been better. We didn't reinforce the corners with fibreglass, just the lumber framing. I can see how a large one could be made lighter by building it with a stitch and glue method using fibreglass. I am not sure it would be necessary to skin the sides.

Ideas and comments:
1. By not using the fibreglass, you will save 10oz of epoxy per square yard. You will need a few coats of spar varnish or exterior grade polyurethane over 2 or 3 coats of epoxy, but the epoxy will save you from having to use more coats of spar varnish. On the other hand the glass-epoxy could save the weight and cost of using thicker plywood, and provide more abrasion resistance.
2. I built a CLC rowing skiff and was impressed with how the glass cloth becomes invisible once saturated with epoxy. I am not sure if polyester resin would provide the same transparency. It doesn't provide the same depth of penetration, adhesion, or moisture barrier to the wood, but you could save some money by only using one or two coats over the polyester-glass, before the varnish or polyurethane. You can't use epoxy before the polyester, but you could use epoxy over the polyester.
3. I think spar varnish might not be necessary. It is designed to be more flexible, for spars that flex. You might get the same appearance with the same UV protection with a less expensive polyurethane.
4. For ideas on how to make a lightweight camper trailer using plywood-glass-epoxy you should check out the teardrop trailer at Chesapeake Light Canoes. It is smaller than what you want, but some of the methods should be similar.
http://www.clcboats.com/shop/boats/development-projects/clc-teardrop-trailer.html

 

Much appreciated, Jamie. Thanks for the link too, I'm really liking the design of those teardrops.

 

Welcome to the forum.

A 10 ounce cloth sheathing will clearly show the fabric weave under varnish. To prevent this, you need 4 ounce or less weight fabric.

A 10 ounce 'glass fabric will not add much strength and stiffness to a 1/4" plywood sheet. You need over twice this weight fabric to make any significant gains in this regard.

Have a look at "taped seam" construction methods, which can eliminate many of the internal frames and supports necessary on a 1/4" plywood structure. To make this work, making curves to advantage is very desirable, as they're naturally stiffer and stronger than flat panels.

Polyester can work, but it has some serious disadvantages on wood. First it doesn't stick very well, so seams tend to open up. It's not very strong, especially in thin coats or over thin fabrics. It's not moisture proof, so the wood will eventually suffer. It has better UV resistance, but it too will break down, without a varnish topcoat. As a rule, taped seam methods only exist because of the physical properties of epoxy. Given the size of the project, you're not going to save much between polyester and epoxy resins. Say a few gallons gets it done and you pay full retail, you might save $20 - $40 bucks with polyester resin. Is this enough of a savings to risk it coming apart?

 

Thanks, PAR. I looked into the "taped seam" (same as stitch & glue?) type construction you mentioned and could definitely see using it in my application. I'll have a 2x3" lumber frame regardless however, so I'm thinking more of a Hybrid stitch & glue, with the frame still there but taped seams for water-sealing and some minor additional rigidity.


If glassing just the seams, would a single 4oz cloth layer (exterior & interior) and sufficient epoxy layers be alright? Then just paint the whole thing in a good exterior oil-based stain?

Too, I'm considering an 1/8 lauan plywood instead of the 1/4 standard for weight savings...any thoughts?

 

Yes stitch and glue is one of the taped seam methods and the most common name applied. There are other names, such as tack and tape, etc., but they're all taped seam methods.

You don't need 2x3 framing on 1/4" plywood. 1x2 will be more than enough and will half the weight of your frame. If the panels are arranged properly, you really don't need frames at all. The taped seams will lock the panel edges and it'll hold it shape fine.

4 ounce cloth is just barely adequate for 1/4" seams. The only time I'd recommend this light a seam tape, is on natural finish jobs. On the inside corner of the panel joints, you'll need a fillet, which will be very visible, so in these locations, I'd recommend heavier fabric (8 - 10 ounce).

1/8" lauan (meranti) if purchased at the big box store will not be a WPB adhesive. Used in an exterior environment, without religious encapsulation, it'll delaminate pretty quickly. 1/4" meranti underlayment can be found at these big box stores (Lowe's/Depot, etc.) and it does have a WBP adhesive.

Lastly, be careful what you wish for. Natural finishes on exterior exposed wood, is about the most difficult finish to care for. You'll be constantly touching it up and recoating it, unless it's garage kept except when out and about. If you paint it instead, you can use heavier tape schedules and it'll take a lot more abuse, before you have to make repairs. Simply put, a painted surface is a lot easy to live with than a varnished one.

Maybe you should post a sketch of what you camper shell might look like.