Fiberglassing Woody for Clear Finish

[campygirl]

We have been mastering the "slow build" and we are 3 years into this teardrop now. We finished skinning it with really pretty 3mm marine grade ply and are planning to fiberglass it now. It looks so good right now, I am really afraid off messing it up at this point.

It is about 90 degrees during the daytime here and we are working in a garage that is not temp controlled but it doesn't get excessively hot. I have done a few practice runs on scrap wood and I think I have found a pretty good technique but have only worked on horizontal surfaces and haven't tried it vertically yet. I am looking for any advice.

1) Should we do a base coat of Epoxy first to seal the wood and prevent bubbles and then do the glass with 2 additional layers of epoxy. I don't own a heat gun and really don't want to buy one just for this. I read somewhere on the forum that a base coat of epoxy might make the fiberglass end up less clear.

2) I really like the idea of applying the next coat after the first one has hardened but is still tacky, but again, I'm worried about the bubbles being permanent. is that a game day decision? ie, if there are bubbles than let it harden and sand them a bit? Also, how bad is sanding when the fibers of the texture of the cloth makes it seem so close to the surface or is it a light run over with 220 grit not likely to damage the fiberglass enough to worry about?

3) In my practice runs, my fiberglass got a little foamy and was almost "gummy" when I was wetting the fiberglass with the first coat. I was just pouring the epoxy and squeegeeing with a hard plastic flat tool (actually a kitchen utensil since my local hardware store didn't care a epoxy tool). I sort of squeegeed the gunk to the edge and wiped it with a cloth and it dried ok but when it happened in the middle, I couldn't do that and it left raised areas. Are those bubbles or am I doing something wrong? Would a regular, window squeegee be a better tool that might avoid this?

Thanks for your help

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[Pmullen503]

My experience is on cedar strip canoes and kayaks which are finished clear.

I apply epoxy thru the cloth on dry wood. As I apply the next foot or two of epoxy, I'm looking at the areas I've just done to check for dry spots. I spot apply more epoxy as needed. I do three coats of epoxy when the previous coat is starting to gel to get a continuous polymerization thru all coats. That's less important on a trailer where the glass and epoxy are there to encapsulate the wood rather than provide the structural strength.

This takes some experience or at least a helper. But you get the clearest layup.

You can apply epoxy to bare wood first and sand BUT you must scrub off the amine blush. Don't try to sand it off, that will just grind it into the surface. You should use a non blushing epoxy. I've used MAS and RAKA and both are good. Not as clear this way and you'll loose much of the chatoyancy of the wood but easier.

Another aspect is the scraping to get the cloth tight to the wood. This will reduce the amount of sanding you have to do. Don't get carried away with too much pressure and don't try to use the epoxy scraped off for anything you want clear: there is too much air mixed in. You can add thickener and use it for fillets or apply it to unseen bare wood if you can't bare wasting it. That may have caused your "foaminess" you were working air into your resin.

You can apply multiple layers of cloth and still be very clear if you don't let the epoxy harden between coats. I routinely use 4 layers of 6oz cloth on the canoe stems and its hard to see the difference between 1 and 4 layers. So if you get a bad wrinkle just cut it open, lay it flat and put another piece of cloth over it and keep going. A lot of block sanding on that spot but it can save an epoxy job.

PS. That looks like Okoume plywood which will look good finished clear.

[tony.latham]

I don't understand why the epoxy foamed. Perhaps you had too big of a batch and it popped off in the container.

I fiberglass over bare wood and don't get bubbles.

This is what I wrote for my book:

For measuring epoxy and hardener, I used pumps purchased from the manufacturer. Raka calls for a by-volume mixture of 2 parts resin to 1 part hardener. To keep from getting confused, I mark the resin jug with a 2 and the hardener bottle with a 1. I do the same on the tops of the pumps.



This would be a good time to recruit some help from a focused individual. Your helper can mix while you spread. There is no room for a mixing mistake, so stay focused and don’t let this turn into a bull session.

I did this by myself, and the system I used was simple. For each batch, I got in a rhythm of two pumps of resin, one pump of hardener, and then two more resin pumps and one more hardener for six squirts per batch.

To keep the mess down, change your gloves after every two batches and never use a mixing cup twice. Have at least two squeegees, and switch to a clean one halfway through the job.

The key to this process is mixing small batches. Epoxy is strange stuff. It starts producing heat as soon as it is mixed, which grossly speeds up the reaction. After mixing a batch, you’ve got about ten minutes if it remains in the container. But once it’s poured onto the cloth, you’ve got a long time. I would suggest keeping the batches to no more than about a half-cup. My six squirts per batch worked out to be about 5 ounces. Make sure you or your assistant aggressively stir each batch for two minutes. During stirring, you are really only mixing the center of the liquid so make sure you scrape the resin off the sides of the container as you mix.
Pour the epoxy onto the cloth in thick lines and use a plastic squeegee to disperse it. Just work slowly, and methodically. Once the resin is out of the container, there is no need to rush.

As you wet out the cloth, remember that some of the epoxy will absorb into the wood, which can lead to resin-starved fiberglass. The squeegee is your stethoscope. It will vibrate over starved cloth and glide over areas of excess epoxy. Keep looking at the layup from a low angle for dull or shiny spots. If a spot looks whitish, it needs more resin. Properly saturated cloth is transparent. Adding resin to saturated cloth doesn’t increase the strength.



Pay attention to the edges of the wall and ensure you have good saturation. If you have a raised spot in the fiberglass, work it flat with the squeegee.

When you think you’re done, take a twenty-minute break and then check to make sure that some of the cloth hasn’t lifted. You can push those spots down with the squeegee. Additional epoxy can be added as long as it’s still tacky.





If I were to take this project on in your heat, I would use a slow-set hardener.

I hope that helps.

Tony

[Pmullen503]

All Tony's tips are good.

Another tip for vertical surfaces (or overhead) where you can't pour and spread. I buy a bag of "chip brushes", cheap, wood handled with natural bristles. Cut off about half the bristles to maybe an inch long. That will make the brush stiff enough. Dip it in your resin and use it to carry the resin to the cloth. Use a dabbing motion on dry cloth so you don't move it. Once wetted, you can use more of a brushing motion to slowly push the excess epoxy onto dry cloth. Avoiding runs will save you hours of sanding. This is much slower than pour and spread so make smaller batches. Toss the brushes frequently and watch out for them dropping bristles (because they will.)

Just a word on spreading vs. scraping; Even though you use the same tool, the action is different. Spreading (moving liquid resin around) can be faster and needs almost no pressure. Scraping uses light pressure to push the cloth against the wood and remove excess resin. If you move too quickly, you get lots of tiny bubbles in your resin and it won't be super clear (and you can't get those microscopic bubbles out with a heat gun.)

If you paint over your epoxy it's not a big deal. But avoiding mixing air into the resin is important if you want a "bright finish"

[Squigie]

I would flip the trailer to do the sides flat - or at least angled, not vertical. But I understand if there is some reason why you don't think that is feasible.

Tony didn't mention it, but I believe he glassed the walls, flat, before assembly.

My only real experience with fiberglass layup was battle damage repair (that didn't have to look good) on difficult curves and complex shapes - often using cotton bags, canvas from damaged litters, or kevlar salvaged from damaged armor plates. Doesn't really translate to fine work with the correct materials, except the battle in keeping materials from slipping/running/drooping.

[campygirl]

Thanks for everyone's input. it was all really helpful. I think the foamy gummy stuff was from too aggressive squeegeeing and I was just using a small piece of fiberglass so there was a lot off fraying at the edges that sort off turns into a gross substance. We are using a slow hardener since we have never done this before, more time seemed like a good thing.

We got 1 coat on. we cut all the cloth pieces and then did the top first to avoid touching the sides when they were wet. I think that was a mistake. The epoxy dripped over the edge and down the sides. We worked pretty fast, but it is a big area and we are newbies, so we weren't fast enough. By the time we started on the side, the overlapped fiberglass was hardening and was never going to adhere to the wood.

We ended up, after a fair amount of swearing, cutting off the overlap as close as we could and putting the epoxy on the sides without overlap. the roof edge looks terrible. We plan to finish the top today with 2 more coats of epoxy (it does look great) and this will let it all dry fully and go back and wash it with soapy water to avoid blush (not really sure I understand that it but it sounds important so we will do it), sand it all down and use 6" wide fiberglass tape to repair it and then finish epoxying the corners and sides.

I don't think we will win an award for technique but I think we can salvage it and it will be fine. It isn't a rocket ship after all (stole that from someone one this forum and thought it was a good thing to remember throughout this process

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[TCJ]

I've done a lot of epoxy work, mostly on boats, and all this advice is good. Here's one more hint I discovered in the past year:

You'll want to change gloves frequently. Epoxy gets on everything and it's difficult to remove. I've found the vinyl "food service" gloves to be the best option in this situation: they fit very loosely, so you can easily slip them on over sweaty hands, and they're dirt cheap so you don't care about swapping them out when they get wet. They're absolutely fine for epoxy. Sam's Club has 2000 of them for $10--less than a penny a glove.

[Pmullen503]

Another tip.

With cured epoxy, use a cabinet scraper to level the high spots. It's hard to sand down a high spot without sanding the area around it. If you don't know what that tool is or how to sharpen one (essential on fiberglass because it dulls quickly). You can use a paint scraper which is easier to sharpen and will work, just not a well or as fast.

Too late for you but it may help someone else: I would do the sides first and let the top edge of the cloth run over. With the epoxy not fully cured but not sticky, cut the glass flush with the top with a razor knife. If you catch the epoxy at the right point it's very easy. If the knife drags or gums up the epoxy is still too soft.

Then cover the top with epoxy/cloth. If you radiused the edge with a 1/2" or greater radius round over bit, you can get 6 oz. cloth to go around the corner, overlapping the sides by about two inches. You'll have to inspect that edge and push the cloth down if it lifts up until it sets.

If it's a hard corner, trim the top glass flush with the sides, let it cure and sand it. Then come back with some 2oz cloth strips, cut on the bias and go over the corners. You don't need full length strips. I'd use three layers: an 8" wide strip, then a 6" wide strip and finally a 4" wide strip IN THAT ORDER (widest strip goes down first). Then when everything is fully cured, sand/scrape it flat and give one final coat of epoxy to seal it up.