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.

 

[s.e.charles]

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.

if you were to figure your labor costs into the fiberglass work vs the premade panels, would it close up the dollar gap and be a better value to buy?

i understand the initial outlay would hurt, but i'm trying to reach and apples to apples cpmparison.

 

[DirtWhiskey]

Echo what other folks said. On a purely cost basis, most people don't value their time into the equation. Also, the TIME you'll spend building it and not camping. But if you love projects, I'd say give it a go.

Keep your eyes on the used market. You might find a shortcut on the time thing. Searchtempest is your friend.

 

[offroadkiwi]

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?

You could do what you suggest, there are some advantages, and some disadvantages.
Fibre glass is not as scary to use as a lot of people think. With boat building I always build the complete hull first as it doesn't have big flat surfaces .
I'm about to build a 4.8m (16ft) habitat box (ply/foam/ply) with 45mm timber studs, top and bottom plates of timber & (45mm thick foam).
I recommend 6oz fibreglass cloth and a marine epoxy resin, slow hardener (unless cold ).
Freshly sand ply first. Must be free of wax, if unsure wipe down with meths.

Lay cloth out on ply and It's important to work the resin very well into the first coat with a fibre-glassing grooved roller. (Small areas can be wet first and the cloth then placed on , but this does not work well for larger areas . You need a wee grooved roller about 80mm-100mm wide, and It's best to have a friend mixing wee amounts of epoxy as big amounts will start to go off suddenly.

I would not contemplate doing the whole habitat in one go, suggest you treat he roof is one job, each wall is one job. While it can be sort of continuous if you have more than one person with a roller, I have always done a surface at a time. Work all bubbles and voids out, then don't persist, walk away.
.
For subsequent coats you need to do one of two things: either continue the next coat just as it sets enough to roll on a second coat and continue with 2 or 3 coats in that fashion, ( the top coats typically lighter that the first coat).
However, once epoxy sets it gives off a waxy substance. in which case let it harden further and the next day sand with orbital sander just to key next coat in and wipe down with methylated spirits between coats (wear a respirator as you don't want to inhale fibreglass).( Cheapest roller clean-up BTW is methylated spirits).
This way is more total time, but less of a marathon and less stressful.
Fibreglass should be painted as soon as practical not left in sun unpainted for too long, as it is not particularly uv resistant.

Four ways to do the external edges .
1) Cover roof and cut flush to edge. Do walls and trim top edges overhang with scissors at a regular distance off the edge and bend over onto roof and epoxy. This leaves no mark on wall and 1 layer on the corner, wont be too straight when viewed from above, but it's typically not seen from above.

2) Do the above but bend both over the corner, you end up with double cloth on corner so stronger. Disadvantage is it is hard to get the line straight and neat as seen from the side.
.
3)...Buy cloth edging tape in the desired width (say 75 or 100mm, width. Before you start fibre glassing draw on a heavy line with a felt- tip pen at distance off corner of half the width of the tape from the corner (ie if 100mm tape lines at 50mm off corner)
When the first coat is on wall or roof, trim cloth with a sharp knife to the edge. Do the other wall or roof surface and trim the cloth to the edge also . The order doesn't matter, but if doing the same day, do the roof first of course. Then sand/scuff to the line (next day). You will be able to see the line if using clear epoxy.
Epoxy edge tape on. This will give one thickness of cloth and leave an overlap line, but it will be straight

4) You can also do both 1 and 3 for two thicknesses and straight overlap line as seen from the side.

 

[rruff]

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.

This would be my vote for sure. Add a layer to the seams later with cloth tape.

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.

I would absolutely challenge that 6-10x cost thing! Unless you are using crap materials your savings will be minimal. Marine ply isn't cheap! I'd like to see you break it down in some detail.

And emulating traditional RV construction is not something you want to do...

 

[Darwin]

I thought about doing this with an Alaskan camper since they are wood framed and I despise its use in a camper unless its had at least penetrating epoxy, which nobody does. Glassed over would be even better, but it would have to be done at their shop before the skins were applied and they basically told me no way. They won't even let you delete the electrical which is a huge mark up. It's a bummer because as far as I am aware besides S2DM's incredible build they are the only ones doing a hard side pop up, which unfortunately is made of wood and I have seen plenty of rotting examples to be skeptical.

 

[Ozarker]

After exhausting all possibilities he may actually do something, in the mean time, you glass the whole project after the box is constructed, it strengthens and covers all joints!

 

[rruff]

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

I made my camper using hand layup FG and carbon with epoxy (E-Bond) on PVC foam (Carbon Core). My 2 cents...

-Beating "premade FRP skin" strength/stiffness/weight is super easy, even the ones that use woven cloth (many are mat/chopped fiber). I did a bunch of tests to verify. Infusion is cool for sure, but I think it's more suited for production rather than one-off. At any rate, hand layup gave me good fiber content ratios and strength and stiffness were what I expected. With 30-35 oz/sq yd FG cloth on each side, the panel weight was ~1.5 lb/sq ft... 1.5" of 4 lb/cu ft PVC foam weighing .5 lbs, and each skin as well. And I didn't consider layup schedule at all. Typical cloth will be weaker and more flexible in the 45 degree direction, but it isn't enough to worry about. Impact is the most important requirement IMO. Also stiffness on some parts like the floor/base, which is why carbon was used (it's nearly 3x stiffer for the same thickness). The floor/base is bolted to the frame via a kind of 3 point mechanism, so if I screwed up, that will probably the first place I notice it...

-Man, the sanding really was a PITA! I decided I wasn't going to care about cosmetics from the start, but it still took a lot of sanding especially at the joints, and the glass/epoxy dust got everywhere... coating me and the entire garage... and it needed to be done many, many times. Not fun at all. Epoxy and cloth are also messy to deal with when doing layups.

-Even though I used cheaper foam and epoxy than you did, it still wasn't cheap! I figure ~$15/sq ft on the FG panels, and that doesn't include every little thing. I did a lot of experiments on pieces made using hardware store XPS Foamular, and the cost and weight savings aren't worth it IMO. It's just too weak and hard to adhere to.

-The benefit of doing my own was that I was able to make it aerodynamic, with curves, rounded edges, and facets. That worked out better than I expected, as the MPG hit is quite small, and it handles fine in cross winds. But it looks rough... definitely no beauty up close.

-Would I do it again? Hell no! Several companies are in the game now, selling panels and full camper builds for a good price. You'd need to really like building stuff to justify DIY on the panels. I'd look into getting some cnc'd and joining pieces with hand layed epoxy FG, which would allow more flexibility with facets and angles. If I even care about that...