First time repairing with epoxy and fiberglass

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First time repairing with epoxy and fiberglass

Postby marcusg » Mon Jul 27, 2020 9:50 pm

So I'm about to do my first ever fiberglass repair on the hole I mentioned in my painting thread (which has gone way off topic.) I already cut the hole out how I want it and made it a gradual slope etc. etc. Greenlake tutored me on how to put a backing on the inside (it's below waterline on the hull.) My question is how the heck do I do the exact steps to repair. Here's what I've gathered from watching YouTube videos (if there's an instructive how-to buried amongst the posts here, please let me know a keyword as "fiberglass repair" & "epoxy" etc. are too general of search terms.)

THE STEPS AS I UNDERSTAND THEM:

1. Clean surface with acetone
2. Prepare my epoxy. 5 parts epoxy to 1 part hardener.
3. "Wet out" the repair surface with above epoxy, leaving a thin layer where repair will go.
4. Cut out patches in decreasing size, with the largest covering the whole 1:12 repair area, and the smallest being the size of the actual hole.
4.a. QUESTION: How do I know how many of these patches to make? And is all fiberglass cloth the same? I've heard about bi-axial 1708 cloth being good for repairs? Are there different thicknesses of cloth? Do I need to measure my hull with calipers and then somehow "add up" the thickness of the multiple layers of cloth so that it equals hull thickness? How do I know the thickness of the cloth?
5. Wet out the fiberglass cloth with the mixed epoxy, either ON BENCH OR ON BOAT ITSELF?
5.a. QUESTION: Do I combine all the patches together, wetting them out individually and stacking them on each other on the bench (on something called peel ply?) and then apply them all at once to the boat, or can I wet each one out onto the boat one at a time?
6. Squeegee out bubbles in the patch(es) of fiberglass.
7. Wait for fiberglass to become tacky
8. Mix some fairing compound into a small batch of mixed epoxy.
9. "Fair" the repair with a squeegee? of some sort to make the boat hull seem more flat
10. Wait for that to dry?
11. Apply some unthickened epoxy as the final layer.
12. Use a piece of sandpaper on a long piece of flexible wood to sand the repair and further fair it to the contour of my hull.
13. Wash all that with soap and water? Then sand with 100 grit and paint.

Did I get that right?

What I need to buy first:

Epoxy and hardener
Fairing compound
Acetone
Some kind of squeegee/scraper
Cups for mixing and measuring epoxy
Fiberglass cloth (how thick? what kind?)
marcusg
 
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Re: First time repairing with epoxy and fiberglass

Postby GreenLake » Tue Jul 28, 2020 4:15 am

Marcus, let me attempt a response, without getting bogged down by answering each point in your list. I think it's great that you are writing it all down to organize.

First, a general comment: If you've never done a fiberglass repair, please do a sample. Why not lay up a 4"x4" piece of laminate 3-4 layers on your bench? That will get you a feel for the process and verify that you've got the mixing process down so it cures properly.

Second, you should cut your fiberglass before mixing the epoxy. Once you have the epoxy mixed, the clock is ticking. Best to move all the prep beforehand.

Third, the type of cloth to use. If you can source expoy-resin compatible mat, I would get a bit of that, to alternate with the cloth. Otherwise a medium to heavy cloth (standard square weave is fine). I don't think there's a need to worry about specialized types for this repair. You should get a rough idea of the bulk you are getting when looking at a dry stack. (Mat might compress a bit, cloth will not). Prepare one or two layers more than you might need, and then adjust as you go along.

Fourth, with a repair that has a complex outline and depth contour, you won't be able to lay up a patch on your bench and have it be a perfect fit. With the "stacked-U" configuration of patches, if one is a bit too long, it will stick out at the edges, where you can then sand it off. So you can get away with making them slightly too large. Obviously, you don't want to overdo that, but it's better than having puddles of pure resin. Cloth is cheap. You can afford to cut one or two extra pieces of intermediate sizes and decide later to skip one of them; much better than the reverse.

Fifth, you can wet a single layer out on a piece of plastic, then transfer that and pull off the plastic. But, unless the plastic can be left in place up to the moment the epoxy cures (which situation you would have if you could prearrange the whole patch), you might find the process a bit messy. Try it out when you do your sample. Or simply do them in place. It would be ideal if you could put the boat on its side to get gravity to help you, as long as it doesn't deform the repair area.

Sixth, be sure to squeegee the excess resin, as long as everything is wetted out (no white areas) you don't want any extra resin. You'll want multiple plastic spreaders of different hardness for this project; also about a handful of the small "chip" brushes.

Seventh, I'm not sure you'll be able to get the repair to come out cleanly below the old surface. You may have to let the epoxy cure (and wash it) so you can sand any bumps back down. Only if you have hollows left after than would you need to use a fairing compound. Me, I use the pre-mixed stuff (like QuickFair) but if you do your own, also test a sample.

Eight, what kind of epoxy to get? Good brands will give you similar performance, but with perhaps some differences. I've been consistently using SystemThree (all my favorite stores stock it around here) and like the 2:1 mixing ratio. With a 5:1, I would have to be more than twice as precise in measuring the hardener, and in mixing epoxy, precision is key. SystemThree's epoxy is sold as "blush free". I've never needed to wash off any blush.

Ninth, you've left out a step: after applying fairing compound, you'll want to let it cure and then sand with a long sanding board: you only want to knock down the high spots, never sand any hollows. After sanding you can apply that final layer of neat epoxy (and then sand again).

Tenth, uncured epoxy cleans up with vinegar. The vinegar will neutralize the hardener, that's why you keep it well away from the repair area, but it's great for cleaning drips etc.. And you'll need gloves. Epoxy doesn't create the powerful smells you get with Polyester, but you can become allergic to it, so avoiding all contact is best.

For measuring and mixing epoxy you can use small graduated painters cups or medicine cups. The smaller the better - you don't want to mix more than you need and if you mix too much at once, it can go off in the pot. Easy to mix more as you need it. Be aware of the risk of unmixed epoxy clinging to the mixing stick, sides, and bottom. Be sure to scrape the stick, side and bottom during the mixing - and then don't scrape the last little bit out when you use it - those last few drops are often not fully mixed and may not cure. (If you keep a bit of epoxy in the cup, you can monitor how it cures, and when you pop it out once hard, you may be surprised to see small sticky patches where it touched the container).

OK, now you have more answers!
~ green ~ lake ~ ~
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Re: First time repairing with epoxy and fiberglass

Postby marcusg » Tue Jul 28, 2020 7:49 pm

Thanks Greenlake. I went ahead and ordered the SystemThree SilverTip you recommended, and also got all the other stuff (scrapers, etc.) coming in the next few days. I'll hold off on the fairing compound until I need it. I know I'll probably need some to smooth out the inside of my cabin and so on, but I don't know which size yet and I don't want to outspend myself too quickly.

One last question: What kind of plastic do I need if I plan to wet out my patches on the workbench and then transfer them to the boat one at a time? I see all kinds of info about peel ply but do I need that for this kind of repair? And your suggestion was to laminate one layer at a time on the workbench and then transfer it while still wet onto the boat, right? So it's just be any old plastic sheeting on the workbench? Also, I don't think I'll be able to turn my boat, so I will be working somewhat upside down. To that end, I got the fast hardener.
marcusg
 
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Re: First time repairing with epoxy and fiberglass

Postby GreenLake » Wed Jul 29, 2020 2:10 am

The fast hardener will still be "slow" :P

Epoxy doesn't cure that fast. To prevent sagging, you may need to tape over the repair perhaps with a stiff piece of plastic, like the window in boxes for store display.

Regular old plastic bags, the clear kind is what you use for backing or protecting your work bench. Zip lock bags work fine. You can cut them open. Also wax paper works.

Do yourself a favor, make a sample. So, for example, take a piece of plywood at the same angle as your hull, or even just vertical, and try to lay up two-three layers on it, you can try brushing on the epoxy, pressing on the glass and squeegeeing it or try transferring it from the work bench. No better way to get the feel for the material and what works for you. If direct layup works, use it. If it doesn't and transfer works better, great. If both turn out to be compromises, you'll know what you are in for. etc.

Your repair will require somewhat precise positioning of odd-shaped patches. That's what makes it impractical to lay up multiple layers ahead of time. Fiberglass cloth will stretch in odd directions as you work with it. You'll learn how to avoid some of that fairly quickly, but possibly not fast enough to jump immediately to a critical repair; hence the sample.

My own "sample" was a bit more ambitious. I used a small plastic tub as a male mold and did a layup of a fiberglass tub which I could use in repairing something that I could afford to toss if it didn't work out. But don't be afraid of throwing away your sample.
~ green ~ lake ~ ~
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Re: First time repairing with epoxy and fiberglass

Postby marcusg » Wed Jul 29, 2020 8:18 am

Yeah I'll definitely do a sample. So what's the point of special plastic like "peel ply" if I can just tape the patches on with regular "store display plastic?" Is there a critical point where I have to pay attention to removing the plastic so it doesn't stay stuck to the repair?
marcusg
 
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Re: First time repairing with epoxy and fiberglass

Postby GreenLake » Wed Jul 29, 2020 9:52 am

Don't know about peel ply. Never used it. Plastic will come off, but you can remove it as soon as the resin turns tacky.
~ green ~ lake ~ ~
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Re: First time repairing with epoxy and fiberglass

Postby Leob1 » Mon Aug 03, 2020 2:30 pm

Some thought from what learned;
Buy twice as many chip brushes as you think you'll need.
To cut your fiberglass have a pair of very sharp scissors
Wear gloves, epoxy is like anti seize
Make sure what your mixing the epoxy in won't dissolve the container (yes I was left holding the rim of the cup)
Don't rush, take your time preparing your work area and materials.
Give it time to cure.
If you really mess up, it can be ground off and redone. It's not the end of the world.
Good luck.
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Re: First time repairing with epoxy and fiberglass

Postby GreenLake » Mon Aug 03, 2020 8:19 pm

+1000 on the number of brushes! (And stir sticks!).

When measuring, be really precise. The "hardener" is not a catalyst, but part of the final compound. It's like a dance: if there are left over dance partners some will have to sit out (i.e. not become part of the cured matrix).
~ green ~ lake ~ ~
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