Skinning your TTT in epoxy and fiberglass

[atahoekid]

There are those of us building Foam trailers. OK, stop the snickering and come to the Foamie section to check it out! Anyway, a lot of the discussion has been on how to skin the foam on the exterior. Traditional wooden canoes were built with a canvas skin filled with a special compound that literally takes weeks to cure and recoat and cure and recoat, etc... Some of the Foamie builders have continued the use of canvas and are glueing it to the foam with glues, paints, lagging compounds, etc. Modern technology has provided epoxy resin and fiberglass. (Polyester resin eats up the foam). There are a few of us on the Foamie site who decided to expose ourselves to the rest of the TTT community to seek some advice and expertise.

Here's what I've planned. 2" thick foam walls, with a 5 mm lauan skin on the interior and a epoxy/fiberglass skin on the outside, creating something of a structural panel or a sandwich panel. So here's my question. Should I thicken the epoxy to get a bit of build up and add a bit of strength (some puncture resistance)or will the fiberglass be strong enough? If it is, I'll just thicken the epoxy enough to wet out the glass and fill in the weave and provide some sanding ability. I'm gonna paint the outside so, being perfectly clear is not a requirement. Can I vacuum bag the panel while I'm glassing and still end up with a new smooth paintable surface?

Thoughts, comments, etc., are welcome

Thanks, in advance, for sharing your knowledge and expertise. Cheers!!

[grant whipp]

Hey, Mel!

I'm no "expert" in fiberglass, but I do have over 25 years in production and R&D, and my brother has been in it almost all of his life. Along with pulling all of the unwanted air out of the mix, vacuum bagging also pulls out all of the un-necessary resin (whether polyester, vinylester, or epoxy) in order to achieve the proper & desired 'glass-to-resin ratio (the same is true with properly squeegeed hand lay-up) ... so, you'll still have to fill in the resulting exposed weave of the 'glass with some thickened resin to get your desired smooth, paintable surface. Some will argue that pouring on the resin with the 'glass will give you the same result, but (especially in the case where the outside "skin" could be considered part of the overall structural integrity of the unit), getting as close as you can to the proper 'glass/resin ratio is crucial ... get that proper strength in there first, then come back and add the finish coat(s) that won't affect the overall strength. If you are worried about added weight with the finish coat, use some micro-baloons in the first fill coat, then sand smooth and apply another thin "skim" coat, prime & paint.

Good luck, and as always ...

CHEERS!

Grant

[KCStudly]

I have virtually no fiberglass/epoxy experience, but am pretty sure that you need to use a peel ply of perforated plastic in order for the excess epoxy to wick out during vacuum bagging. Don't recall the proper name for this special product, but it allows the excess to squeeze out through the perferations and thus be able to peel off after the fact. Leaves a very even pattern of small "pips" on the top bagged surface and a slightly rougher texture than the mold side ("mold side" doesn't apply in your engineered panel application).

Any one with any vacuum bagging experience knows what I'm talking about. Novices may want to do some more research.

[Larry C]

Mel,
I am glad you started this thread. I hope it becomes the place to discuss the use of glass and epoxy without stepping on the the toes of those that prefer other methods. We have a home


I think you may be better off using the plywood on the outside, glassed, and finishing the inside with a single layer of light glass. My reasoning is the amount of glass/epoxy required to get a dent resistant and structurally sound exterior may weigh as much as 1/8" plywood. With plywood and a thin layer of glass on the outside,and another thin layer on the inside would be much stronger than glass on one side only.
Vacuum bagging is always the best way to get the lightest and probably best layup, but for a one-off project it's not really required. Hand layup has been done forever, and good results can be obtained. However, if you have the equipment, by all means bag it. As Grant points out, the proper glass to resin ratio is important for structural integrity, and bagging will give you the best ratio.
Most first time users tend to use way too resin and end up floating the glass on the surface. There are many methods of applying resin to glass. They all work but some are easier than others. I have tried them all, and settled on what works best for me, others have different opinions. Also the type and weight of the glass you use will determine the amount of epoxy required to fill the weave.
If you glass on the bench while the walls are flat it will be much easier to get good results.The glass I now use gets the wet-out coat and one fill coat before sanding...that's it! What I hate to see is builders leaving the the epoxy lumpy with an orange peel finish and thinking it's just fine. You need to fill the weave enough to be able to sand it smooth.

This 1/8"wood strip panel that is now glassed on one side only weighs 4# This is my inside wall covering. I think light weight wood covered with glass can be very light weight.

Larry

[Wobbly Wheels]

This thread was needed, thanks for setting it up.
As a primer, anyone new to epoxy can pick it up in a nutshell by reading the user guide for West Systems epoxy.
http://www.westsystem.com/ss/use-guides/
Their free quarterly mag, Epoxyworks, is worth signing up for (and they don't appear to sell their mailing list to others)

I'm using a foam/ply sandwich for my floor and then EPS/6oz (X2) for the shell. It will have the nose of a horse trailer to keep wind resistance down, which would be difficult to fab in plywood. I'm towing with a 4cyl pickup, so weight is critical. The GVW on the reg is 700kg, but only because that's the max allowable without trailer brakes installed. Structurally, it's probably closer to twice that, but that's the gross I'm building to and I would never get there with ply, given the size I want.

Build thread

This thread started with Mel asking about puncture resistance, so I'll offer my .02 there:
On its own, 6oz over foam will protect from things like branches scraping along the sides, the grit of road spray, etc. It won't help you for actual punctures like windblown branches and wayward shopping carts. For that you might want to back the epoxy by skinning the outside with 1/8 ply. If you want to use a thickener, put it on AFTER you do the layup with unthinned resin. Thickened resins will give you problems with starved patches because it's more difficult to wet out the cloth properly.
If you are looking to give the epoxy a harder shell, you could thicken your first fairing coat with fibers or wood flour instead of microballoons. It will be tougher to sand, but it's the first coat so as long as it's reasonably level you can knock down the highs with an RO sander. Then you could build up with resin thickened with the much lighter and easily sanded microballoons (microspheres, etc). That will add a bit of density to the layup right where you want it and still make it easy to get as fair a finish as you want. With microballoons, you'll also need a final sealer coat before paint.

[atahoekid]

Thanks for the answer to my question about the durability of an outer coat of fiberglass/epoxy. I'd just as soon not try to skin with 1/8" ply so I'm thinking unthickened epoxy to wet out, first fairing coat thickened with wood flour and subsequent/final fairing coats thickened with microballoons. Thanks for your input. Much appreciated.

One other question? How much strength (puncture resisitance) do I gain by going with heavier cloth? In your opinion is it worth it?

[Wobbly Wheels]

Mel, there's a huge gain in using a heavier cloth - 6oz is really just for sheathing to help with epoxy's inherent brittleness. It's really a 'starting point' or a 'bare minimum', there are plenty of heavier and more structural options. I have some bits of a heavy structural cloth (Dynel) that I use for 'hard points' in a layup. Dynel is a trade name, but it's like 'Kleenex' - it's a heavy cloth that combines both 90 degree and bias roving stitched together. I use it most often in lieu of butt blocks for assembling long hull and deck planks from 8' ply sheets. The down side is that it takes a lot more epoxy to wet out so, while it's a low profile and low weight option, it's definitely a more expensive way to go. I burned through about $40 worth of epoxy today and the only actual cloth I got down was about 15sq ft of 6oz...the rest was fillets, sealing ply, etc.

One option might be to use something like a 12" Dynel tape around the rockers of the trailer and maybe up the front wall. If you put it on before the 6 oz sheathing, the finish will be continuous. Anything that penetrates that layup would probably punch through plywood anyway. What you need is up to you, so maybe try laying up some cloth on a piece of foam and see if it's what you like - you can go with a heavier 90 deg cloth (called roving) or a structural cloth like Dynel, or Carbon/Kevlar, etc. It's all about what you need and what your budget looks like.
I'll grab some pics of the stuff tomorrow.

I'm kicking around the idea of allowing for one of those rotating boat racks you see on slide-in campers - a bushing secured with Dynel could be a quick and easy way to build for it, whether or not I actually use it. I'm starting to layout the side panels so now's the time...


______________________________________________________________________________________

Some reference pics I thought might be handy:
This is the resin I use most. It's runny so it wets out really well but it can suck up a lot of filler - good thing filler is cheap !
That amount of resin was about $150.

This is cabosil, a structural filler. This is a fibrous powder that makes the strongest epoxy adhesive you can come up with. It can be combined with other fillers to customize your adhesive, but should be added first since it takes a fair bit of resin to wet it. Those clumps are from the rough 'hooked' ends of the fibers that do the job, once it's stirred in it blends smooth. If you are using a lot of it, wear a dust mask as it's an irritant and you'll be sneezing for sure. This pot was about $7.


Microballoons are tiny glass bubbles that break when they're sanded, which makes them an excellent fairing compound. Being mostly air, the compound is lightweight and easy to sand. The texture is identical to flour. Again, about $7 for that pot.


I assume everyone knows this stuff but if not, here's a neat trick for cutting cloth square:
With a 90degree cloth, you can usually pick or pull out one of the threads to give you a clear line to cut the piece off: just cut along that line and your cut edge will always be square to both sides.

[Larry C]

Brian,
I stopped using 6 oz cloth 20 years ago. I don't think a foamie needs that heavy a cloth. I use 3oz for everything, extra plies here and there if needed. Also, Dynel sucks up a lot of epoxy, and adds weight. I thought one of the ideas of the foamie was to save weight. I would think multiple layers of thin glass laid on a bias would offer the same advantage of Dynel without the extra weight.

[Oldragbaggers]

I love this thread. Finally a "place of our own" where us fiberglass aficionados can come and discuss openly.

[Wobbly Wheels]

Absolutely Becky - we can kick this can around without fear of being made fun of by the other kids in the class...

Larry, I hadn't even thought of using lighter cloth over EPS foam because the foam itself is so compressible. I would expect it to dent just from everyday use, like road debris and the wayward shopping carts I mentioned. Still, you've gotten me thinking about using it inside cabinets, etc.
Over wood or PVC core foam though ? Absolutely.

I've found Dynel to be far better for abrasion and puncture resistance than multiple units of cloth regardless of how they're laid. About 5 years ago, I banged off a punt out of some leftover red cedar that would slide on top of my canopy. One of the problems I was having was with the bow getting chewed up on the rocks on launching and landing. I tried going heavier on the glass, but I still had to replace it. I had some Dynel left over from another job so I put a strip across the bow at the waterline. Now, I just slap a fresh coat of paint over the scratches and it's good to go. Since them I've been a convert.
It does indeed soak up a lot of resin but its function is simply to hold that resin and add sacrificial density, like against rocks or to protect against punctures in a foamie. Hence my suggestion to use it on the rockers and maybe the front of a TD but not as a skin.

My thought as far as hardpoints is that it would still be lighter than the backer of hardwood or ply that one would normally use, so long as it's laid up to spread the loading gradually.

Of course, the ultimate lightweight puncture-resistant option is aramid (Kevlar), but $$.....

[Larry C]

I see what you mean about using Dynel for abrasion resistance in certain spots. Similar concept to the stuff used on lower sections of auto/truck bodies to help prevent stone chips. Can you bury dynel in epoxy or is still kind of lumpy?

Actually, I was considering using Carbon/Kevlar hybrid cloth on my trailer top over 1/8" ply. I have used a small amount of red/black on a kayak and it looks cool! The problem is I don't want to pay for more than one layer, but unless I find an analine dye the right color, the wood will probably show through the hybrid cloth.

Larry

[Larry C]

I love this thread. Finally a "place of our own" where us fiberglass aficionados can come and discuss openly.

I agree... It's been a long time coming!

[Oldragbaggers]

I am going to be skinning my sidewalls with Okoume marine ply (3mm), my roof with baltic birch ply (1/8"). The entire body will then be covered with 6 oz. fiberglass cloth and epoxy resin. This is over a sandwich frame (see my pic below) which will have the rigid pink foam in the spaces. First of all, if anyone sees a problem with the strength of this combination, please speak now before I screw it all up.

Now, my question......
I was wondering, for those of you with more experience fiberglassing over plywood than I, do you usually put a coat of resin or CPES on the plywood before you lay up the cloth? I was just thinking that if the top layer of the ply was porous, and I was taking proper care to squeegee out all excess resin, then if the plywood absorbs the resin, wouldn't that starve the cloth of resin and leave voids between the cloth and the wood, or in the fibers of the cloth? Does the kind of ply you use make a difference? I don't think subsequent layers of resin would help fill voids once the first coat had hardened beyond those that are right on the surface.

I laid up cloth over the road side of my floor (which was baltic birch ply also) but I coated it with 2 coats of CPES before I covered it with the cloth and 2 coats of resin. I wouldn't mind the extra step or expense of pre-coating the wood for the walls if it will make a good difference, but if it isn't necessary, I would prefer not to waste my time and money.

What say all you glass experts?? I hope to start glassing this weekend.

[NathanL]

I have always encapsulated the wood with epoxy (the same as I use with the glass - West Ssytem) prior to fiberglassing. I came from boatbuilding and that is the standard procedure, but some people do and some people don't. No need to go overboard. I would say that 99.9% of all fiberglass jobs that aren't vacuum bagged have way too much epoxy and about 50% have just too much lol. Don't try and fill the weave on the first coat. I have always tried to just get the glass to stick and get rid of the white spots on the first coat then go back and fill in the weave on the second coat. Everyone has their own way.

Dynel is more abrasion resistant which is why you see it used on decks of boats instead of fiberglass but it's also relatively heavy and as someone mentioned soaks up resin.

I know nothing about working with foam. I have wondered if anyone used a sandwhich of foam and lite-ply (I don't know the offical name but I use it on 40% scale R/C airplanes) that weighs a lot less than traditional ply. The outside plys are chinese birch or poplar or some sort and a core of I have no idea but it's pretty spongy with lots of voids but it would provide a puncture resistance and comes in thickness down to 1/8" (actually a little less). Aircraft Spruce as well as speciality wood places carry it in large sheets.

The term someone above was looking for when vacuum bagging is breather cloth which comes in a couple different brand names or just "breather cloth" or "bleeder cloth" and is applied over a release film.

I've never really put much thought into reducing weight of a trailer so I'm not help there. I pull with a 3/4 ton truck and only build/use small trailers for the size where a normal travel trailer wouldn't fit.

[Larry C]

Becky,
I do it both ways depending on how much time I have. I think the seal coat will give you the most consistent results. Both the plywood's you are using are hardwoods, so the epoxy (I would only use regular epoxy) will soak in more evenly than over a soft wood like Cedar, but you could do it either way if you want to save time.
I am from the school of light is right" When I seal coat I let the epoxy soak in awhile and where ever there
still shiny spots that I cant squeegee off, I wipe them with a paper towel. I want a nice uniform satin finish to the seal coat. Shiny spots are just excess epoxy that adds weight.
As I mentioned in an earlier post, I don't think 6oz. cloth is needed especially over 3mm hardwood plywood. It will take probably 3 fill coats to fill the weave and IMO add a lot of unnecessary weight and $ Also, I hope your doing the side walls flat on a bench instead of vertical.

Larry