Fiberglass cloth on plywood: order of operations

[ReluctantTraveler]

I'm exploring/planning a plywood exterior flatbed truck camper (wood framed with foam board insulation), and exploring adding more structure and water protection by glassing the whole thing with fiberglass cloth and epoxy (like the West System).

I'm considering if its worth glassing the plywood sheets before installing them onto the frame, and then doing some touch-up glass work where the screws/nails are afterwards.

My thinking is that it would be far, far easier to do that than to try to glass an entire 12' long box + cabover sleeper in one go. In particular, re-epoxying the roof, and glassing the underside at all, seem like they'd be rather difficult.

The tradeoff, of course, is that if you glass it all at once, you essentially end up with a single almost-molded shell.

Am I missing some other compelling reasons why glassing first and then touching up is a bad idea?

 

[S2DM]

You’d be far better off buying premade panels from someone like Terraops (CMP) or similar. Even for very experienced fiberglass folks like myself building your own panels is a lot of work and achieving the right strength to weight ratio at home is very challenging. There is a lot that goes into calculating a glassing schedule, laying it all up etc. And for the novice, you then end up with something very heavy that requires an absolute ton of sanding to look decent. Ask me how I know

Plywood is a poor medium for a lot reasons. It’s heavy and it really takes some work to get resin to penetrate. When plywood is used in a marine setting, where weight isnt a big concern or even a benefit, I’d start with a penetrating epoxy (like smiths) that is not very viscous and penetrates deeply into the wood as a hot coat. This basically allows fingers of epoxy to go deep into the wood and seals up the outer layer so that when glass is applied it really bonds. And then go with a fiberglass skin. You could def glass each panel first, but then you’d have a ton of secondary bonds to join the panel and all that just adds weight. When you dont do an initial hot coat, the plywood slowly sucks the resin out of the glass as it penetrates the wood and you end up with delaminations and poor bond strength later. A guy local to me made his own camper by using two thin plywood skins and pour foam. He didnt pre-treat the ply with any sort of hot coat as described above so basically the only thing holding the two skins together is the very light adhesive strength of the pour foam. He’ll eventually see tons of delamination.

I built my own using divincel and they are extremely strong, but the reality is that they still weigh a fair bit more than they should. I’m in the midst of a new build and am doing all the secondary bonds via vacuum infusion, but I’m using premade panels for the bulk of the build.

 

[ReluctantTraveler]

You’d be far better off buying premade panels from someone like Terraops (CMP) or similar. Even for very experienced fiberglass folks like myself building your own panels is a lot of work and achieving the right strength to weight ratio at home is very challenging. There is a lot that goes into calculating a glassing schedule, laying it all up etc. And for the novice, you then end up with something very heavy that requires an absolute ton of sanding to look decent. Ask me how I know

Plywood is a poor medium for a lot reasons. It’s heavy and it really takes some work to get resin to penetrate. When plywood is used in a marine setting, where weight isnt a big concern or even a benefit, I’d start with a penetrating epoxy (like smiths) that is not very viscous and penetrates deeply into the wood as a hot coat. This basically allows fingers of epoxy to go deep into the wood and seals up the outer layer so that when glass is applied it really bonds. And then go with a fiberglass skin. You could def glass each panel first, but then you’d have a ton of secondary bonds to join the panel and all that just adds weight. When you dont do an initial hot coat, the plywood slowly sucks the resin out of the glass as it penetrates the wood and you end up with delaminations and poor bond strength later. A guy local to me made his own camper by using two thin plywood skins and pour foam. He didnt pre-treat the ply with any sort of hot coat as described above so basically the only thing holding the two skins together is the very light adhesive strength of the pour foam. He’ll eventually see tons of delamination.

I built my own using divincel and they are extremely strong, but the reality is that they still weigh a fair bit more than they should. I’m in the midst of a new build and am doing all the secondary bonds via vacuum infusion, but I’m using premade panels for the bulk of the build.

Great advice on hitting the wood with some epoxy first (I think the West System install videos talk about that, too).

Pre-made panels would certainly be easier. They're also 6-10x the cost. At least a few folks here have had good luck framing out their rigs. Hell, that's how most traditional bricks-and-sticks RVs on the market are built.

 

[S2DM]

Great advice on hitting the wood with some epoxy first (I think the West System install videos talk about that, too).

Pre-made panels would certainly be easier. They're also 6-10x the cost. At least a few folks here have had good luck framing out their rigs. Hell, that's how most traditional bricks-and-sticks RVs on the market are built.

Check out idasho’s build. His has been on the road for years now without issue.

My two cents is that at the end of the day. It won’t be cheaper. I started out with the same notion but the west stuff is expensive, quality glass mat is expensive. It just all really adds up over time.

All that said, building my own rig with my own two hands that wasn’t perfect but won awards was a really life defining moment and set me up for success in other areas (camper building is such a multi disciplinary endeavor, I think you emerge smarter .

So go for it. Just keep your eyes open along the way as things present themselves about better ways to do it. And defining principle = KISS - keep it simple stupid. Our new build
Is positively spartan compared to our first. But it’s got everything I need in spades and none of what I don’t.

 

[ReluctantTraveler]

Check out idasho’s build. His has been on the road for years now without issue.

My two cents is that at the end of the day. It won’t be cheaper. I started out with the same notion but the west stuff is expensive, quality glass mat is expensive. It just all really adds up over time.

All that said, building my own rig with my own two hands that wasn’t perfect but won awards was a really life defining moment and set me up for success in other areas (camper building is such a multi disciplinary endeavor, I think you emerge smarter .

So go for it. Just keep your eyes open along the way as things present themselves about better ways to do it. And defining principle = KISS - keep it simple stupid. Our new build
Is positively spartan compared to our first. But it’s got everything I need in spades and none of what I don’t.

Yea, Kenny's rig has been a huge inspiration from Day 1!

Interesting about the cost, though. I can absolutely see how all the little things you don't think about add up over time.

 

[S2DM]

Yea, Kenny's rig has been a huge inspiration from Day 1!

Interesting about the cost, though. I can absolutely see how all the little things you don't think about add up over time.

Ask my wife about that she has the actual amount written in blood somewhere I’m sure. We ended up close to triple. Quality composite stuff when you aren’t buying commercially and in bulk is brutally expensive. A panel kit from cmp I thought was really pretty reasonable and even though I have a dedicated shop and a lot of experience, I really can’t come close to their strength to weight ratios. A note on that though is how you camp. My wife won’t camp within a mile of anyone and after trying to shoehorn our 550 down goat trails, we’ve gotten smaller and lighter over time. Some folks are totally fine with big heavy rigs and mostly camp in established campgrounds.