View Full Version : Polyester Mess

Jack G
08-08-2003, 07:50 AM
I'm coming down the home streach with my Bolger "Bobcat", and forgive me Father, I have screwed up ! In sealing the inside of the hull with 20% thinned polyester resin, I've apparently undercatalized the mix. It's coming up on two weeks since application and parts of the coat still are tacky. We've had very hot and humid weather during this period. Can I overcoat with CAREFULLY catalyzed polyester and kick the first batch, or will it eventually cure by itself? I want to prime and paint the interior so the deck can go on, this year would be nice. Help!

Bob Adams
08-08-2003, 10:28 AM
Ohhhh....why oh why would you use polyester?
back before I saw the Epoxy light (years ago!) I used quite a bit.If you used the right resin, the stuff with wax, it will kick eventually.If you used laminating resin, without wax, it will not. I would put another coat of the proper stuff over it then swear off polyester forever!

ion barnes
08-08-2003, 12:12 PM
Nooo, don't do it. The second coat will not mix with the first. Yes, in time it will kick off, as you are using promoted resin, it already has a small amount of catalyst added before you bought it.

So; how much catalyst did you use, and how did you measure it? Were you using waxed or unwaxed resin? What was the temperature at the time of your misfortune?

As for the detractors of polyester resin, file, and carry on. Epoxy has its advantages, but depending on the scale of the job, polyester still has considerations. Ion

Todd Bradshaw
08-08-2003, 12:15 PM
Yep, it sure sounds like you used a resin made for laminating, not surfacing. Laminating resin will stay tacky on top in order for the next layer to bond to it. Another coat of resin rolled-on (thin one - no reason to add a bunch of unsupported resin and extra weight) which contains a surfacing agent should do the trick. If you can find it, you can also just add a bit of surfacing agent to the resin you already have. It's usually styrene monomer mixed with a little parrafin. The wax floats to the surface, cuts off the air supply and the surface hardens-up. On that boat, it would probably only take a couple spoonfulls of surfacer to do enough resin to coat the inside.

I suppose at this point you could probably even overcoat it with epoxy, which generally sticks better to polyester than more polyester, but it's a bit "experimental" in nature and it may be safer to just stick with polyester. Do plan to switch to epoxy for future projects. Once you do, you'll never look back.

bob goeckel
08-08-2003, 12:39 PM
i had the same problem a while back. i ended up scraping alot off then recoated with resin with surfacing agent added and it worked fine. FGCI has the surfacing agent on their web site or i can get it for you locally. it doesn't take very much but it sure helps when sanding the final coat. it seems to be the humidity that causes some of this problem.

[ 08-08-2003, 01:40 PM: Message edited by: bob goeckel ]

ion barnes
08-08-2003, 01:03 PM
I whanted to wait for Jack's reply to my questions before I make any suggestions but will make one comment.

An aquaintance of mine surfaced his sundeck with fg/polyester and at one point had done a topcoat of waxed resin on a hot day. It remained tacky thereafter till he topcoated on a cooler day. The reason offered as why the one coat remained tacky was that the resin kicked off too quickly and did not allow the wax to rise to the surface. Parts of the deck that had remained in the shade during that first topcoat did not have the tacky feel.

08-09-2003, 10:34 AM
Just a side comment. I made my first and only boat with polyester resin cuz' I didn't know any better. I was told at the time to thin the first cote with styrene. I did that. I think I just coated the final coat with paint. The 100% acrilyc latex paint stuck well. ;) I just had the boat out for the fist time this third season. I keep looking for problems, but none so far. :D

The next boat will be done with epoxy, but I wanted to get by as cheaply as possible on the first one. In many ways I succeeded in learning a lot!

08-10-2003, 03:27 PM
I'm glad to hear there is another Bobcat being born. Jack, I hope you enjoy yours as much as I have mine. You might try removing some of the mess with acetone..it's possible it would work but a good scraper will probably be the best bet.
I used polyesther on my boat with good results, although I did have one such incident as you describe. It's been several years now and I can't remember exactly how I resolved the problem (they say the memory is the first to go....) At any rate the stuff has worked just fine and the boat is still in very good condition.
On another note, the gaff jaws have presented a problem on my boat and I have increased the thickness to 3/4" and went to solid oak. No problems with them in the last two years since I've done that. I've learned to sail in her and she has been an excellent teacher. Post some pics when you launch!! smile.gif

08-10-2003, 09:16 PM
Just paint over it- the paint will seal off the oxygen that keeps it tacky, allowing it to finally cure, and the tackiness will promote great adhesion to the paint. Try a test patch if you don't believe it.

Buddy Sharpton
08-11-2003, 09:25 AM
Conrad has given you the short way home here. I recoated unwaxed polyester in the bilge of my fiberglass sailboat years after it was built with ordinary oil based enamel and it worked fine. A test is a good idea. Loje Todd said too, an epoxy would be a good idea May I suggest Pettit makes a very tenacious, hard finish two part semigloss white epoxy that would be perfect for this application I think. Just roll it on with a fine finish foam roller like from WEST. Real forgiving, great body, not thin like LPU, and not soft like "regular" epoxy primer. A real good one shot expedient on boat interiors.