more on glass repair

ok, so looking back on this little fiberglass repair adventure of mine, i was wondering why i needed to use any “special” sort of resin. is there any reason why i couldn’t have just used any good two part epoxy (waterproof) or even just used gelcoat/paste (which essentially is just an epoxy, right?), as long as i saturated the glass well? as a reminder, all i was doing was putting a 3 layer glass patch over 2 cracks (not holes) in a carbon ski.

any thoughts?


No UV protection For The Epoxy
and it will break down in sunlight after awhile. There is color tinting that can be added to epoxy which supposedly offers some level (not equivilent to gelcoat) of UV protection.


When I dropped my QCC from six feet …
If it was just a crack that was not wide open through the glass I would have just used two part epoxy without any fiberglass cloth.

I prefer the West Systems little packets since I know they are quality, but when I couldn’t get them I used the two part stuff that you get at Wally World or Advance Hardware.



gelcoat/paste (which essentially is just an epoxy, right?),

Gelcoat is a form of polyester resin
Just wanted to complete your thought.

I always use epoxy for repairs
It bonds well to all other composites and it’s much stronger than polyester or vinylester resin. As others have said, it needs to be protected from UV. Gelcoat, paint or exterior varnish do that well.

Can you put a glass patch on the inside with epoxy resin and then use gel coat or marine paint on the outside of the hull?


– Last Updated: Jul-14-05 1:59 PM EST –

No (Polyester over epoxy). Practically, yes. It works, although not recommended (by the suppliers). Painting, I don't know. It'd be interseting to do a test on that, actually. As long as the surface is keyed correctly (rough enough) to accept a mechanical bond, because that's what you are getting, any epoxy will work. Workability would be in question with the 'two part epoxies' - can you saturate fiberglass with it?

Personally, I use polyester on a polyester (fiberglassed!) boat, and epoxy on an epoxied (wood/fiberglass) boat.

Polyester is cheaper and easier to mix in small batches (and tolerant of mixing irregularities) particularly down to 1oz or less - a common amount for repair jobs. polyester resins can be obtained off the shelf in smaller amounts (but then, epoxies are available over the net in small quantities too - a pint or so). If you want to mix epoxy in small batches, syringes work well to ensure the quantities are correct.

Both epoxy and polyester resins age over time (polyester quicker than epoxy, though). Oh, and with polyester you can control the cure/working time somewhat.

Thanks Brian
I wanted to make sure before I put it up here, then fogot… GH

I use measuring spoons to mix up the correct ratio in small batches of epoxy.

West System
repair epoxies are available in small packets, pre-measured for small jobs. Available from West Marine.


I have some real old epoxy patches
which have shown no significant degradation from sunlight. One is on the side of a boat I car-topped and used almost every weekend for two years.

Rather than weaken the epoxy with pigment, and make the repair harder because with pigmented resin it is harder to see whether the cloth layers are wet out or not, I would either skip the pigment, or just spray paint over the final hardened patch. The spray paint will stick better if the amine blush is removed with alcohol or soap and water.

Actually, epoxy is not a lot stronger
than vinylester, only a little. Vinylester comes very, very close to epoxy in all respects. It just isn’t as handy for spot repairs because “promoted” vinylester resin does not keep… it will start gelling in the container. A clean glass container will keep it viable longer than any plastic, but “go off” it will.

Vladimir Vanha of Noah also insisted that his vinylester was just as strong in its ability to adhere to a surface as epoxy. I did some repairs with his vinylester, and they all held up really well. Still, I use West epoxy exclusively now.

JackL… use the cloth on inside of boat
Using resin alone is really futile.

Because West epoxy will keep for
several YEARS with the metering pumps in the cans, one can store them for use whenever patching or little projects arise. After a couple of years, the hardener thickens slightly and turns reddish, but the resulting mix still hardens just fine. (West data confirms this.)

Small amounts are easy enough. One squirt from the big can, one squirt from the small can, and you have about enough for a four layer glass patch over a 3" break.

Control setting time? Usually I use 205 hardener, even in hot weather, but 206 will slow hardening quite a bit.

West epoxy will bond really well to epoxy, vinylester, and polyester. West offers a variety of interesting fillers and thickeners, including graphite powder, aluminum powder, a couple of real basic pigments, colloidal silica, fibers for reinforcement, and microballoons. Mixing epoxy and microballoons results in a light tan filler which is light enough to float.

West fillers…
…which can also be used with polyester.

Although epoxy bonds well to poly, visa versa is not true.

Controlled setting time? Of course, you are using additional hardeners, wheras you use the same hardener for polyester in different quantities. Polyester comes out more cost effective.

Having said that, I do like working with epoxy. Any repair I do on a fiberglass kayak, though, will be polyester, not epoxy.

Although I don’t doubt West Systems data, new epoxy/polyester works far superior to ‘old’ stuff.

Yup, I Like The West System Epoxy

– Last Updated: Jul-14-05 7:40 PM EST –

I keep the can of resin and hardener around with the pumps in. Convenient since I am either making surf fins or patching dings in boats. I think the 205 (2 hour hardener) is probably the best for small and simple repairs. Nothing beats 3 minute epoxy from hardware stores though if you need something to stick and stick fast.


Resins & paint

– Last Updated: Jul-14-05 8:28 PM EST –

Most boats are made with one of three resins, Polyester, Vinylester or Epoxy. Polyester which I have used is the cheapest, most brittle if the hull needs to flex and considered the least friendly to people and enviroment. For example its' catalyst can cause blindness. Vinylester which I haven't used is cheaper then epoxy, but more then Polyester, handles flexing without cracking and is considered to have good laminating/adhering qualities. Epoxy is the most expensive, is safer to work with, will flex and is considered to have the strongest bonding power of the three. Epoxy will bond to the other two, but they are suspect for bonding effectively to each other or epoxy. I have worked with a variety of brands and some have more quirks then others, but the West System is always a safe bet.

Tricks I have used on some homemade glass boats I have built is the use of Auto Bondo as a filler to fair a hull or as a poor man's gel coat. I built my boats outside of a mold so gel coating wasn't an option and the hulls were painted. Bondo would have to be covered with a paint to waterproof. If one doesn't want to use expensive marine primers and enamels I have used Home Depot sealer-primer paints like Prime-it or any primer paint designed to keeps stains from bleeding through and they adhered to the epoxy like glue. Household exterior enamels can then be used if budget is an issue.

Now if you really want to give a boat a real makeover, go to a fabric shop and buy a lightweight rayon like fabric with let's say a Hawian print on it and epoxy that over your last layer of glass and after that cures, put a couple coats of UV Varnish on.

I’m aware of “epoxy” for different uses, and I wonder if they are the same. Here’s what I mean:

I use 2-part epoxy (PC7) for structural repairs to Royalex. (And also use 3M “urethane adhesive,” which I understand is not an “epoxy”?)

And, I’ve used 2-part epoxy resins for soaking fiberglass and Kevlar cloth for repairs, because they are better than “polyester resin.”

Could I use PC7 (mixes quite thick as a filler) to impregnate cloth?

Also, for repairing a wooden paddle, what could I use to make an epoxy tip?

And, to strengthen a paddle blade, is polyester resin sufficient, or should I use epoxy resin?

I get all these products/applications confused. Posts like this help.


Ooh… I Like The “Hawaiian Shirt” Idea!