Fiberglass, what did I do wrong?

[mxtommy]

Hi!

I'm doing some fiberglass repair on my boat. Yesterday I laid the first layer of fiberglass yesterday with no issues. I mixed 9 ounces of resin with 108 drops of hardner ( Can of resin mentions 12 drops to 1 ounce). Like I said everything went ok.

Today I went to put down a second layer of mat. I found yesterday that I could have used some more resin, so I tried making twice as much (18 ounces). I mixed in about 200 drops of hardener, then set to work. I had just put down the mat, went to put more resin on the mat, and found that the resin I had mixed had already set to the point that it was unusable. This was within a few minutes of mixing it, many times faster then the resin had set yesterday and much too fast to be usable.

Is there a reason the mixture would have set so fast? I could understand if I got the ratio wrong, but it's not that hard to count to 200 , so I don't think that's it. Is it possible that when you mix more, it generates more heat and so then sets quicker?

I'm laying another sheet tomorrow, did I do something wrong today?

Thanks!

[Stillraining]

I always use less then they say...I think your hypothesis is correct..."bigger batch less needed".

FWIW reson will set up with out hardener......eventually.

[okawbow]

It seems to me, that the more resin I mix in a bowl, the faster it kicks. It just heats up faster, I guess, because of less surface area to weight.

[olson34]

Sounds like you could be using poly resin, but the problem is similar with epoxy.
As soon as you mix in the hardener, the reaction starts. This generates heat. The more heat that accumulates, the faster the reaction occurs. The more liquid you have in your container, the slower the heat generated can radiate away...
So, if you need to mix a larger batch, use a wider container or tray that lets the resin spread out and thereby let heat radiate off quickly.

Sidebar: a friend of mine once had a fairly large amount of glass to lay, and had no experience with epoxy... so he mixed the whole quart with the hardener... in one coffee can. Very shortly it started to smoke, and he had to toss it over the side!

Several small, well-spread-out batches are better.

Cheers,
L

[Freesail99]

If you are using epoxy resin, I hope you used the correct mat.

[scottyt]

as was said spread it out to a thin layer. a paint pan works well for this so does plastic plates ( hard plastic not foam ), then the cured stuff pops off for reuse.

another thing is you need to mix as you add it, if you dont you start the curing real fast where the drops are puddling. i has seen poly literally start curing in 30 seconds where the puddle was then smoke ( literally ) the whole batch solid in another min from the chain reaction from the heat.

[CalebD]

Mixing epoxy resin with the hardener produces an endothermic mixture which produces heat as others have noted. The more heat the faster the cure time.
You did not say which brand of epoxy you are using but it matters little as the advice to spread a big batch out in a thin layer is the way to go if you are using a big batch. Ambient temperatures also can make a big difference in cure times as well as the size of the repair you are trying to do. Higher temps always = faster cure time and less pot life.

[scottyt]

he is using polyester guys..... 12 drops to one oz

[GraemeInCanada]

You don't need to use the exact amount of hardener for polystyrene type of resins. It'll kick off, just mix it well. The more you put in the faster and as others have already said that the more you mix up the faster it'll kick off because it's getting hot. Do small amounts at a time, set up two sets of containers if need be, get the amounts ready to mix. When you're done with one, set it off to the side and have an assistant refill the containers to be ready to mix. Then grab your second set, mix them quick and get back to work. A well oiled team can do well with this idea in mind.

[mxtommy]

Wow. Thanks for all the information

Scottyt's right, I'm using polyester. I'll be putting in the last layer today. Unfortunately I have no assistant, but if I get two small containers ready I should be more than good. I'm not doing that large an area

Thanks again!