Epoxy .... "What", is a "Drop"?

[SURV69]

I have an old boat(1967), a plastic boat.

I bought some resin and epoxy for fill holes, in order to redrill the holes.

I set the mix at 10 drops of hardener(per instructions), per 1oz of resin.

I made the mix went back into the boat and "forgot", what I was doing ... all I got was a nice replica of the mixing cup with a stirer in it.

So, I made up a new batch of 2-1/2 oz, and put the 25 "drops", in it.

Now the temperature os just into the 80's, so I expected it to set up faster than the earlier batch.

Within 2 minutes, it was set and almost hard ... in the cup ... with the stirer.

Now I'm wondering ... what is a "drop"?

The hardener does not come with a pin to make a hole, and it doesn't have a hole ... so it needs a hole.

So, even though I used a rather small sewing needle, I wonder if the needle was too large, making the drops, a little too large.

How can a company, sell this stuff and expect the end-user to know what size to make the hole in the hardener?

[jongleur]

I'm guessing that a certain viscosity
will "drop" at a certain rate regardless
of the hole size.

[jeremiason]

You can't change the ratio of hardener to epoxy resin, but you can get slower acting hardeners.

My guess is that you are using a fast acting hardener in hot weather.

Wherever you bought the epoxy at, go back, explain the situation. If they agree with me, ask them for a slower acting hardner and my advise is get one with a hand pump, instead of using drops, because it is more accurate.

Also there are lots of You Tube videos on the subject here:
https://www.youtube.com/results?sear...g+marine+epoxy

[TurninTurtle]

Epoxy is exothermic (gets hot) as it cures. The hotter it gets the faster it cures.... the faster it cures the hotter it gets. Large batches of fast curing epoxy CAN burst into flame due to this effect.

Typically epoxy mixes in ratios of 1:1 to 4:1 Resin to hardener. The poly resins are the ones known for just a few drops of catalyst per ounce.

Epoxy is sensitive to the mix ratio and being off 5% can greatly affect the strength of the epoxy. You'll have useless rubbery goo or super brittle weak epoxy before you alter the ratio enough to greatly affect cure time.
HIGH TEMPERATURE can cut working time to less than 10%...

Poly resins are tolerant of a wide range of catalyst... Just residue of catalyst from mixing a recent batch on a toothpick dipped in a 5 gal container of poly resin can cause it to completely cure over a few days.

Anything reasonably close to the right mix with poly resin and it will be fine (for strength). More catalyst will cause it to cure faster, but you'd need a chart from the manufacturer of the ratios @ temperatures for cure times.

10 drops per ounce is a LOT of catalyst for poly resins... Generally recommended ratio is about 100:1. 10 drops per ounce would be close to 50:1 "big drops" could push that to 25:1.

And there is how you can check your drop size... dispense drops into a graduated cylinder. You'll need to dispense a lot of drops or have a small, accurately marked graduated cylinder.

What most people do though is learn the effect of their common drop size (which is really pretty close to the same regardless of pinhole size, its more a function of the fluid being dispensed) and adjust the mix ratio according to results.

Note that cure time varies with temperature and this effect can be VERY large.

[jongleur]

If you're using a thickened epoxy,
you can mix it on a board and keep
it spread thinly. That will keep it
cooler and it will not set as fast.
Cups don't work so well as you've
experienced.

[SURV69]

Thanks ... I suspected that generally speaking a drop, is, in fact, a drop, for that particular liquid.

The instructions call for 10 drops per oz, with a 12-15 minute period before hardening.

The first one ... I completely blew it(hot boat ... fell asleep).

The second batch ... 1-2 minutes it was hard jelly at about 82 degrees ... just checked weather ... 92 degrees.

No more sleeping and quicker dispensing in the future ,,,

[TurninTurtle]

I've even used a shallow, wide paper bowl, floating in ice water, to slow the reaction.

Then you get into... the coatings on the paper can affect the cure. so you have to find uncoated (really cheap) paper bowls. Work fast because the water will take the bottom out of the bowl...

[bletso]

With epoxy I have had good luck putting the mix in the fridge. For filling holes, I mix it and dispense a little in a small plastic cup, use it and refill. In 90 degree heat I have used my small batch to do 50+ holes over an hour. I don't like loosing even one stoke of a pump mix, the stuff is expensive. Make sure to use slow cure hardener. Fast cure will definitely hard as fast as you experiences.

If you are filling holes also use either colloidal silicate or a filleting blend. It will kick faster though.

Definitely get the pumps as mentioned. Good luck.

[Jim Cate]

Drop size will vary with viscosity, and viscosity is a function of temperature, so there are some other factors involved. I have done the icewater bath trick, but using plastic cups or ice cream containers etc, and it does extend pot life considerably. But again, it changes the viscosity considerably, so if using a thickener to make a heavy paste when it is cold, by the time you get some to the job, it may become runny... I have truly botched a job via this mechanism... what a mess!

Jim

[SteveSails]

Are you sure you are using epoxy and not polyester resin? Almost all epoxy resins that I know of specify a volume ratio such as 1:1, 2:1, 5:1 and have a fairly long working time. The polyester resins or fillers like 'Bondo' use only a few drops of hardner and set up very fast if you over do it. Double check what you got and let us know.

Steve

[Cheechako]

The bigger the batch the faster it cures. It may actually smoke and get real hot. It helps to spread it out in a shallow container instead.
The ratio does seem weird for epoxy though. often 50/50 or up to 3/1

[SURV69]

Jim ...does that mean that at 95 degrees, a drop migh t be bigger? If so, I was getting a double whammy

Steve: I'm afraid I used epoxy as a generic term ... it's polyester resin ... for a polyester boat

[TurninTurtle]

I have epoxies with working time as short as 30 seconds...

I have small bottles labeled:
30 sec
1 min
5 min
15 min
30 min
2 hr

Supposedly the 105 resin + 206 hardener West Systems epoxy is 2 hr work time... I have had it harden in the mixing cup in 5 minutes due to high temperature and not getting it spread out in time.
The exothermic reaction can be impressive...

Then there's slow cure, finish cure, and "regular" (doesn't say slow or finish)

The time is appx time between start of mix and when it starts to stiffen.

Slow cure and finish cure take longer between when the epoxy stiffens and it isn't sticky to the touch like not quite dry paint. These ARE still flowing a bit until they are no longer sticky, but they won't form a good bond if you try to make something stick.

Longer cure time epoxy will form longer molecular chains and stronger bonds. But the bond generally is only as strong as what you are applying the epoxy to. Hardwoods tend to break before even the 1 minute epoxy fails.

***************

I also commonly use about 30 other types of glues.

[Cadence]

Originally Posted by SteveSails

Are you sure you are using epoxy and not polyester resin? Almost all epoxy resins that I know of specify a volume ratio such as 1:1, 2:1, 5:1 and have a fairly long working time. The polyester resins or fillers like 'Bondo' use only a few drops of hardner and set up very fast if you over do it. Double check what you got and let us know.

Steve

That was my question also. It sounds more like polyester from the catalyst mixing instructions? If so ambient temp. is a huge factor.

[pcmm]

Originally Posted by SURV69

I have an old boat(1967), a plastic boat.

I bought some resin and epoxy for fill holes, in order to redrill the holes.

I set the mix at 10 drops of hardener(per instructions), per 1oz of resin.

I made the mix went back into the boat and "forgot", what I was doing ... all I got was a nice replica of the mixing cup with a stirer in it.

So, I made up a new batch of 2-1/2 oz, and put the 25 "drops", in it.

Now the temperature os just into the 80's, so I expected it to set up faster than the earlier batch.

Within 2 minutes, it was set and almost hard ... in the cup ... with the stirer.

Now I'm wondering ... what is a "drop"?

The hardener does not come with a pin to make a hole, and it doesn't have a hole ... so it needs a hole.

So, even though I used a rather small sewing needle, I wonder if the needle was too large, making the drops, a little too large.

How can a company, sell this stuff and expect the end-user to know what size to make the hole in the hardener?

First of all you aren't using epoxy. you're using Polyester resin. Epoxy just isn't catalyzed like that! typically its in ratios 5:1, 2:1 etc. Poly resin is really hard to work with once the head and humidity get up. Get some epoxy resin. Yes it's more expensive, but its much easier to work with and creates a much stronger secondary bond.