Resin not hardening...WHY?

I put 3 layers of glass and poly resin on the bottom of my boat, letting each layer dry before moving on. Everything went really smooth and all resin set up nice like it should. Then the very last spots that I did on the final layer, there are a bunch of spots that won't set up. Even after a day or two, still tacky. I tried going over them with more resin with lots of hardener, so it should have hardened in about 5 minutes, but its still tacky the next day. Did I get a bad batch or is it the humidity. I'm at a loss here, and wasting resin. Any help is appreciated.

 

You could heat it up to ~70-90 Celsius with a hot air gun or with a halogen light. 10min in higher temp should be enough.. be aware of the fire risk..

 

Hello Bill
I am no expert on glassing but I have ran into the same problems before.
In my case what it was. the hardner, It will go bad quickly after its opened and even quicker if left in the sunlight. What I do now anytime I am going to glass anything is get fresh tubes of harder and mix up a small test batch. This way I can make sure the ratio is right for the temp. and the hardner is good.
Tom

 

I guess you are talking about polyester.
With epoxy, miscalculating the ratio can lead to the same result.
Low temperature can considerably lengthen the time to cure. In the winter I had a model which took four days to cure in 18C, (with a very bad type of poliester).

 

Uneven cure:

-bad mixing
-scraping the last polyester from the mixing cup, and using it. (polyester which is on the walls of the mixing cup is hardly mixed with curing agent)
-MEKP gone bad (less likely, then the whole batch would take longer to cure (geltime drift)
-resin gone bad (again, not likely. Old resin gets lumpy, but luckily still cures. It can be filtered through a stocking, then used.

 

I know it was mixed good, especially the stuff I put over it to fix the problem, I made darn sure to mix it alot. The resin and hardener are both new from the store, and I didn't scrape any out of the cup, I dabbed it with a brush. I emailed 3m and they said to wipe the spots with an acetone soaked rag and that should fix the problem, but I don't know why. Maybe I'll try a hair dryer first.

 

The acetone will dissolve the uncured stuff, and perhaps a waxy layer.

 

Adding extra hardener is not a good idea . The ratio for epoxy is critical. You need to remove the bad spots and relaminate.

 

Poly! not epoxy..

 

Sorry about that.

 

PATCHY cure , mmmm !!! causes that i can think of
Not mixed peoperly would be my number one , was the container round or square ? round containers the catalyst can and does go up the sides and cling when you stir , Square containers the catalyst does the same but the 4 corners never get mixed properly and its quite hard to do a 100% MIX IN a square container .
When you say its still tacky doesnt mean that much !! what about the resin is it hard or soft ? can you scratch resin off with you fingernails ?? .
If you have used waxed resin and it been sitting in the drum for a while all the ingrediance thats in the resin starts to separate out and this happens quiet quickly if the tempratures are up , light stuff floats to the top ,heavy to the bottom , even the promoters in the resin will separate as well , so if you didnt shake or stir or mix the resin container before you started thats another possability .
By the time you got to the bottom all the goodies that are left are basicly the dregs with stuff all good stuff in it as you have used all the good stuff already .

Glass is another possability !!, if its been laying around on a floor or even leaning against a concrete wall ,it could have moist patchs and being damp the moisture kills the resin and it will never reach it full potentual hardness ever !! even if you try to cook it with lots of heat .

Even a brush or roller thas been in a pot of acetone or what ever you have used to clean you gear and not shacken out properly can do a simular thing by dilluting the resin to the point where it has little guts left in it .

Again its like poking a stick in the dark ,with out actually seeing what you have got all we can do is speculate as to the causes .
Remedy is easy !! just grind it off and reglass it , simple and done !!

 

One other thing I can think of:

In factories where epoxy and polyester are both used, keep both resins and all their tools (brushes, rollers, bubble busters, buckets splashing full of acetone) away from each other.

A brush that has been used in epoxy, then cleaned in acetone, will render the complete bucket of acetone and their contents useless for polyester use. The amine of the epoxy can have the effect of the polyester resin not curing.

 

Yeah that another possability .Polyester dosnt like epoxy thats for sure !!!!!

 

While I'm no expert on fiberglassing I would try heating the spots first to try to harden them up (I once did a 38" rc tug out of the stuff poly and 3 layers of 6oz cloth over a male mold) I had a similar problem that after about a week there was still a problem with it fully hardening in a few places, so I tented the whole thing and heated it to 110 F and in about 20 minutes everything had hardened up. However like I said I'm not anyones expert on resins. I hope this helps.

 

I had a problem with the sealing coat of poly on my small boat build, I had not let the stain dry long enough. The resin was good, because the same batch on previously coated surface hardened as it should. My boat is light enough to carry so I took it outside in the sun on two days (reached surface temperatures of 60-70 deg celsius) and the resin finally hardened so I could sand it normally.

L