Polester Resin

[Memphis Mike]

Does anyone have any experience with polyester resin? I am building a Bolger/Payson design { Diablo } that I have glassed with 2 coats of 6oz. cloth and poly. resin. I live in a hot moist climate { Memphis Tn. }. In Payson's book, he says to use a little less than a teaspoon of hardener to a pint of resin for hotter drier weather. This is what I have done. Remember, I live in a hot moist climate. Where the resin was applied to the cloth it cured with no problems. Where it has come in contact with already hardened surfaces { it has been days now } it has not fully cured and smears when I sand. Also the plans call for 2 coats of resin on the interior bare plywood to seal it before painting. I have found that when I apply it to bare wood it will hardly cure at all. { takes weeks } Should I add more hardener and work faster or what? I haved talked with some experienced builders who have not been able to provide an answer. Everyone is using epoxy.

Memphis Mike

[Jeff]

My first thought was that you must not be using enough MEKP, but 1 teaspoon should be about right for 1 pint.

http://www.fiberglast.com/UsefulCharts/catalystcon.htm

I've been using Epoxy for so long now that my mind immediately went to mixing, but that really is never a problem with Polyester (one of the nice things - I did undermix epoxy once and had a situation similar to yours where my epoxy never cured and I had to scrape it out and redo it which was a huge pain - at least with Polyester you should be fine as you can put a catalyst rich coat over the top and the MEKP should cure the resin below.)

Is the MEKP you're using new? It does break down with age and sunlight I believe. You might try getting a new bottle and seeing how that goes, at least a test sample.

What brand of resin are you using? Have you tried getting a gallon of another type?

I've never worked in your conditions (it's pretty cool here, 75 in the summer max) but if you have to use more catalyst, maybe try putting the resin in flat dish like a flat paint roller tray rather than a jar or can, as the greater surface area will help extend the time you can work with it.

I have heard of a few people cooling the resin down before they start working by storing it in a really cool place, or on the extreme end, even dunking the container in ice water prior to mixing.

Your resin may not be promoted. Make sure the resin is promoted, typically with Cobalt Napthanate. Vinylester resins typically require 0.3% CoNap by weight and 1.25% MEKP. Polyesters might be similar. Any fiberglass supply house should have it. You can definately get it from Mahogany:

http://www.mahoganycompany.com/

5450 Atlantic Avenue, Mays Landing, NJ 08330-0099
609-625-8101, fax 609-625-8209
E-mail:info@mahoganycompany.com

If it is not too late you may want to consider using epoxy. It is a far better adhesive, and alot less smelly.

One other thought is that polyester (and vinylester) resin is air inhibited, which means that it will not cure in the presence of air. This is a problem on thin layers. Wax is sometimes added which floats to the surface and isolates the resin from the air, allowing the resin to cure.

the wood itself might be the culprit... some woods contain tanins which inhibit polyester from curing... especially in 'knotty" areas.

since most of it seems to have cured this probably isn't the case but ya never know...

as a last resort, cut out the uncured areas of cloth and resin, wipe it all down with acetone, and try again...

a good trick to keep in mind is to spray PVA over your lamination to exclude air from the surface. it prevents that gummy film from forming and reduces sandpaper load-up... a lot. get it from your FRP supplier

[Lew Morris]

something to keep in mind... these resins generally do better in thicker sections... resin that is merely painted onto a surface never gets very thick, certainly not as thick as it is laminated with 'glass.

since the stuff cures exothermically (makes its own heat) thin sections sometimes do not make enough energy to kick. if you are going to use it simply as a coating... double up the catalyst (a nuke batch) to compensate for the thinner coat... but work fast my friend.

[sharkeymarine]

If you are coating wood by all means use epoxy. Polyester is very brittle and tends to crack very easily in thin areas. I would even say that if you are just coating under a floor board to seal it, you wouldn't even need the cloth. Epoxy is just such a great sealer as well as strength too. http://WWW.SHARKEYMARINE.COM