I am doing some repair work on a vinylester boat. Is expoxy resin tha best choice and will I be able to gelcoat over it?
Thank you,
Chris Brown

Chris, I would not use epoxy if you are going to gelcoat over it. Gelcoat is just polyester or vinylester resin with pigment added... Epoxy will stick well to poly and vinyl but not the reverse. I would stick to a poly or vinyl repair. It is also cheaper.

I'm always happy to chime in with a contrary opinion, so here goes....

vinylester/polyester is cheaper to be sure, but in my experience it's temperamental with regard to mix ratio and curing conditions (temperature, humidity, etc).

Epoxy on the other hand is tough to screw up. the mix ratios are 1:1 or 2:1 or 5:1 instead of 40:1 for polyester, so you can be off by a little and still be OK. System Three epoxy in particular has given me good results in some really crappy weather conditions, and they sell small-repair kits so you don't need to invest in the full $80 gallon of resin. Of course, you can't apply gelcoat over the repair, but that's a non-factor to me since I hate gelcoat anyway. i can never seem to get the color right.

If you have white hulls, I'd suggest an epoxy repair with a painted finish. the beauty of paint (particularly spraypaint) is that you can feather out the edges to blur the boundary of the repair, which makes color matching less critical.

Either method, it's important to work with a smile on your face. If you're all cranky and frustrated while performing the work, it will show in the final product. cum ba yaaaaaaa....

Actually there is an epoxy you can gelcoat over. I think it was SB-112. Also lots of good general information is this manual. http://www.fiberglasssupply.com/pdf/epoxy/epoxybook.pdf

Has anyone thought about, or tried to, add tint to epoxy? If you have white hulls and could just tint the epoxy white...viola! No gelcoat necessary. It's certainly possible to achieve a nice smooth finish with epoxy (although it does take some doing).

I've added white pigment (available at hardware stores that mix their own paint) to West System Epoxy with good luck. I'm not sure if it was chemically proper, but it worked for me.

Jack Hoying
Fort Loramie, Ohio
Prindle 18 #1645
http://www.bright.net/~jmhoying/sailing/prindle.htm

oooo hey....just found this. You'll probably find this of interest.

West System and Gel Coat

When I reworked the bottoms of my P16 I added west system white pigment to the epoxy. It looked good for a year, then started to yellow. I will paint the repair this year, one advantage to tinting the epoxy, or even polyester is if you paint it and the paint is scratched, it will still be white in the scratch.

Chris,

There was a pretty good discussion of the topic at the end of last year.

Click here for the thread.

A tip on mixing poly and vinyl resins: add the hardner and begin mixing ... when you think it is thoroughly mixed you are exactly half way done.

Use the vinylester. Buy the red tinted MEK so you can see it's mixed. It is not hard to kick properly. Make sure the ambient air temp. is within whats called for and have at it. Vinylester is a good product.

Mike

As a baot builder I like repairs to be done in the original material. Using epoxy over vinylester is not always good, and we always remove all traces of it if a job comes into our shop with epoxy over vinylester/ polyester. My reasons are:
the hardner in many epoxies is incompatable with polyester gelcoat and will stop it curing.
In my experience many epoxies are not weather proof and will simply peel off after a period of time. (west system is no problem!)
The mixing ratio on poly/vinyl is not critical and unless its way out the resin will usually go off no matter what.
Epoxies go yellow and look terrible.
Use of epoxy will usually cause problems finishing with gelcoats not sticking. (again west system has few problems)
Jim Boyer