Epoxy vs polyester vs vinylester?

A coarse 3M Roloc sanding disk in a right angle drill will take the M-Tex down quite easily. Then build back up using polyester.

There is a lot of glass on the bottom of these boats, just because you blew through the gelcoat does not necessarily mean you need to re-glass. A couple layers of gelcoat may be all that's needed, especially if the hull bottoms have a curve to them. If they are starting to wear flat, then yes, I would suggest glassing. Also depends on whether or not you use wheels. If you aren't dragging your boat around a lot, then you're not going to put wear on the bottoms.

sm

The reason gel coat doesn't stick well to epoxy is not the epoxy per se - it the amine "blush" that occurs on the epoxy surface when it cures - especially when the air is humid. Remove the amine (mechanically or chemically) and provide a rough profile for the gel to mechanically attach (coarse sanding) and gel will stick to epoxy just as well as it will stick to cured polyester.

Polyester will only chemically attach to itself when the layers are still tacky and "green" - not fully cured. That's the way the boats are built originally.

That Marine-Tex is so old and worn down that all the amine is surely gone by now. Rough it up (80 grit), clean it, shoot your gel and hope for the best.

Matt, what you say makes perfect sense. I was t sure if there was more to it than that, but it's good to know that the two can be bonded mechanically without issue. However, I had already this weekend chipped out the old epoxy with a chisel and set up some new fiberglass. Maybe it wasn't necessary, but at least I know that it's built back up the right way with plenty of strength.

It seems that the previous owner must've consistently lifted the port hull and dragged the boat up the beach, wearing a very flat spot in the outboard side of the starboard hull. It seems he tried coating gel coat over some already fractured glass, and when the spot was still flat, he built it back up with Marine Tex and then faired. Looks like it was ~1/8" - 3/16" at it's thickest. It took 4 layers of cloth and it probably could've used 1-2 more. Thanks srm for pointing out that a lot of exposed glass doesn't necessarily require new glass. Comparing to the hull template, my bottoms were still pretty close to original shape, with the exception of the removed epoxy. I'm waiting for warmer weather to fair the fiberglass and roll on/brush on some gel coat.



Jumping back to the topic of the EPO's, I've sanded down my third coat of epoxy, and I'm ready for paint. Glad to be done with the graphite dust!!! Given that peeling paint is what started me down this road, I'm a little apprehensive. I'd hate to have to strip them down and do this again in a year or two. For those that have painted their EPO's, I'm curious how it's held up. Any peeling? If the paint gets chipped/peeled/damaged, do you have to sand the whole rudder down to resurface, or is it easy enough to touch up and sand fair? Does type of paint seem to make much difference?

I've decided that I'm tired of sanding my rudders, and I think that any paint poses a danger of chipping, flaking or peeling off (maybe only with improper application or abrasion, but still), and I'd hate to have to sand them all the way down to the epoxy to re-coat in the future. Besides, it sounds like most people are using an epoxy paint on their rudders, which wouldn't seem to be any more or less UV resistant than the underlying surface. I sanded them down to 800 grit. I might buff & polish them, too. I'll just be sure to take them off and store them inside when I'm not sailing.

Back to the hulls:
I have to say, the polyester cures damn hard! Forget sand paper, I had to take a file to it to fair it in! Didn't get it perfect, but it's close, and I figure that gel coat sands/fairs a lot easier than the fiberglass/polyester combo. I think I understand why the previous owner used Marine Tex! Didn't use fiberglass Mat, as I've heard you should between layers of tape, but I figure just having glass & resin there has to be better structurally than the epoxy that was there!

That said, yesterday I moved on to gel coat. Now, I'm trying to find the most cost effective way to reasonably restore/improve the quality of the boat without going way over the top. Obviously you'd pretty much have to re-coat the whole boat to make it look like new, but I opted for new gel coat on the bottoms and then just buffing & polishing the rest. That said, I'm worried that in hindsight I might've made some dangerous concessions with the prep/finish on the hulls. I roughed up the bottoms with 100 grit, wiped it down with acetone and rolled on my first layer of finishing gelcoat (all I had on hand, left over from 2 years ago). It catalyzed quicker than expected. We got a thin coat on before it gel'd. My brother suggested that, in the interest of saving time and gel coat (I only had a pint total), we don't sand the first coat, thinking that the second coat would better fill in the low spots and allow us to sand fair without removing as much material. So 4 hours after applying the first coat, we wiped the new stuff down with acetone to (hopefully) remove the finishing gelcoat wax agent and applied the second coat, a little thick. However, now I'm starting to think about it, and unless we were able to get good chemical bonding between the first and second layer of gelcoat (unlikely at that stage), without sanding the first layer, the second layer might want to peel off pretty easily. Does anyone have any thoughts or suggestions on this? In hindsight, foregoing the sanding for acetone probably wasn't a very good idea, but it's what we did. At the time I was thinking the only reason we needed to sand between coats was the wax, I wasn't thinking about the bonding surface. Planning on sanding it fair tonight and then buffing, polishing & re-assembling the boat tomorrow. I really hope it works out, I'd hate for all that work to go to waste.

First coat:


Surface after coat 1 hardened:


Second coat:


I'm just hoping that I haven't made a mess of my boat that I'll need to come back and spend a lot of time fixing later, but sailing season is here, and I'm itching to get back on the water.

I've repaired three or four sets of original EPOs. The ones that I painted over the epoxy still look good (actually I painted, then wet sanded, then polished). They are also on my racing boats and the rudders are typically covered when not being used.

One set I just epoxied but neglected to paint. That was for a beach boat that sat on the beach all summer in the sun and the epoxy turned cloudy and will have to be re-done. Note that I didn't use any graphite filler on my rudders, just straight resin. Everything thing I've heard/read/seen with epoxy is that unless it's UV stabilized epoxy, it needs to be covered otherwise it will turn cloudy/yellow in the sun.

Like I said, on my rudders, I just shot them with two or three coats of rattle can paint, then a quick wet sand to knock down the surface imperfections and then a coat of wax or polish to bring out the shine and provide protection. I haven't noticed any chipping or peeling of the paint at this point.

Regarding your gelcoat job. I think you probably do need to sand between coats if you're using waxed gelcoat in order to get good adhesion for the next layer. But rather than sanding off everything you've done, I'd just leave it for the season and see what happens, maybe you'll get lucky.

sm

Thanks srm for all your advice and guidance, it's been invaluable. I will probably scuff up with 320 grit and put a coat of paint on my rudders soon. I'm still pretty confident that extensive UV damage and poor surface prep were the cause of my original issues.

I ended up just sanding my bottoms fair and leaving them. So far it seems to be adhering. Hopefully I got some amount of chemical bonding between the two coats. Some pictures below:


My gel coat color matching wasn't quite perfect, but it's close enough! If you're more than 10 feet away, you can barely notice the difference! It's the bottom, anyway, haha.



Why don't they look as shiny right side up!?!


I used a $40 variable speed buffer from Harbor freight, wool & foam pads, 3M Rubbing Compound & 3M Finesse-it II, and wow, what an improvement!
All in, it was ~$280 for materials & tools for the fiberglass, gelcoat & buffing, and another ~$200 for the rudders. Damn that stuff adds up quick!

A few lessons learned for next time (hopefully a LONG time away!)

Rudders:
1) Sanding graphite & epoxy makes a mess!
2) Sanding epoxy is tough, but a power sander and low grit sandpaper will burn through it faster than you think
3) Bubbles are unavoidable. Mixing in graphite entrains air in and of itself! But stirring slowly with a popsicle stick and applying/drying in direct sunlight helps thin & smooth the finish.
4) Foam Roller followed by foam brush to smooth the surface is the way to go!
5) When resurfacing, you will find soooo many more surface imperfections than you ever knew you had!

Hulls:
1) Don't forget that polyester resin/gelcoat shrinks as it cures. When applying fiberglass cloth, always cut 1 or 2 more pieces than you think you need.
2) Just because there's glass showing doesn't mean you need new glass on the bottoms. Check the shape of the hulls using a template before planning the repairs.
3) Applying gelcoat on thick doesn't pay. You've got to sand more, which takes off all the extra gelcoat you put on!
4) Brushing gelcoat on seems to result in a better finish, but rolling covers more area. If rolling, use very light pressure!
5) When gelcoat starts to gel, quickly trying to put more on just makes a mess of the finish!
6) Curing polyester/gelcoat is STRONG. I'm finding dead bugs everywhere! - Some well ventilated space not attached to your house is advisable.
6) Don't sand too much with the low grit paper, remember there's a long way to go! Sand up to 1500 grit using very gradual steps. Skimping on the sanding, especially with the higher grits will leave visible scratches in the finish!