Epoxy - A batch gone off

Problems, how to use. Also see: "EPOXY", in the left-hand column of the Home page.

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Rational Root
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Epoxy - A batch gone off

Post by Rational Root »

I started to glue up the Centerboard case today. I sanded the Oak and precoated it with epoxy.

Then I mixed up a batch of epoxy and filler, but while I was working on one side of the CB case, the remaining epoxy and filler was just getting warmed up.

When I went back to the mixing cup, it was hot, really hot, and had a big solid lump in the middle.

By now I had a half glued up CB case, and no epoxy ready. I mixed up a second smaller batch as quickly as I could, but still making sure I stirred it enough. So now I have to wait until tomorrow evening until I can see if it glued up OK.

Wish me luck.
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DanH
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Post by DanH »

It is surprising the first time it happens to you. It is also very interesting to watch it happen. If it ever starts to happen while you are holding the container you are using to mix the epoxy in, remember to put it down as quickly as possible. As you saw, when it goes it goes fast and it gets very hot.

Mix small batches at a time and use only wide shallow mixing containers. A tall narrow container almost guarantees excitement. Mixing is also an art at some point and one gets better each time.

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Rational Root
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The CB case seems ok....

Post by Rational Root »

The CB case seems to have glued up ok.

I tidied it up today, added a few bronze ring nails for good measure.

There was a hole to be drilled through the Oak at the forward end of the case the would have been whole lot easier to drill before I put it all together. The main problem was not drilling the hole, but cleaning up the break out from the drill bit. Since the line to raise the Centerboard is deadended through this hole, a little rounding of the sharp edges was required.

It's amazing where you can fit a dremmel.

Next step is the keel. I need to clamp it in place, and tidy up the CB bed logs to fit. Then I have to cut the slot for the CB through the keel.

That's one of those jobs that if you mess it up, there really is nothing else to do but start again with a new peice of wood. An a clear 4" x 1 1/8" x 12' is an expensive peice to mess up - never mind the time it took to cut and plane it.

Again, wish me luck.
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Jones
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Post by Jones »

Placing the mix in a nearby freezer (if convenient) will arrest the catalyst w/o damaging the product. Some builders use an iced cup under the mix cup to retard the catalyst. Narrow/tall cups produce the highest amount of heat.
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GeorgeD
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Post by GeorgeD »

Hi Dave,

I got caught out in exactly the same way today, even after reading your post yesterday! :oops:

I mixed up 4 squirts of West resin with 4 squirts of hardener with microfibres. A few moments after starting to apply it, I felt it heat up and saw smoke coming off it. I put the cup outside for safety, and this is what it ended up like!

Image

I reckon it was about 24 degrees here today (our one day of summer probably) and I just wasnt ready for it in that kind of heat. Winter will probably be back in our neck of the woods in the next few days so we should be ok again!

cheers,
GeorgeD
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Jones
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Post by Jones »

4 squirts?

It sounds like you are relying upon a dispenser system for accurate ratios of hardener:resin? I think you'll be much better off purchasing an inexpensive mail scale that reads in grams... a decisively more reliable method of determining mix ratios with epoxy!
Avoid Haste.

GeorgeD
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Post by GeorgeD »

Hi Mr Jones,

Thanks for your advice. West Epoxy kits come with "mini pump" dispensers which they say gives the correct ratio. See page 8 of their manual - http://www.wessex-resins.com/pdf/English.pdf

I calculate that I was using 120g of mixed epoxy, then added enough microfibres to make it a thick glue.

As it says in the manual, "a plastic mixing cup containing, say, a 200g mix can generate enough heat to melt the cup".

This is a case of RTFM first for me I think!!

Dave - what quantities did yours go off at?

thanks
GeorgeD
What's the rush? Getting it finished?!
Zip project started: January 2008
Project site: http://www.hartdale.co.uk/blog/

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BruceDow
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Post by BruceDow »

I am also a big fan of the calibrated mixing pumps. They are fast, easy, clean and convenient. I have never had an epoxy problem, so must assume thaty they are accurate enough for our purposes.

As for the volume required for epoxy to kick... any volume will. (It all sets, right?) It's just that larger volumes create more heat when they go)

With the West System, you can buy Fast and Slow hardeners. I generally use Fast for gluing, but, if it is hot outside, and I have a tricky glue-up to do, I will use Slow. The Slow gives much more working time, but the obvious trade-off is that it takes much longer to cure.

Sometimes I mix Fast and Slow to create my own "Medium". (Just make sure to keep the TOTAL amount of hardener in line with the target mix ratio)
Bruce.

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Bill Edmundson
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Post by Bill Edmundson »

In hot or cold weather, I keep my epoxy and hardener at around 70 degrees. That helps make it easier for me to predict working time. I use the pumps with no problems. Lots of small batches. I haven't done a lot of fillets. So, I don't have a good feel for it. I use mini bread pans for mixing. The aluminum helps dissipate the heat. I think, I might try a pie pan for a fillet mix and keep it spread out.

You can also freeze some water in one pan and nest your mix pan in it, to control heat.

Bill
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Rational Root
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All told, about 150-200ml.

Post by Rational Root »

Including the filler, I had about 150-200 ml in the cup when it went off. I use painter's mixing cups. Picture the large soft drink cups from Mc Donalds, only without any wax on the inside.

I also mix with one of these on a cheapo cordless drill...

Image

A tongue depressor, cut off flat at one end, duct taped to a disposable chopstick. Works great.

Wear eye protection - sooner or later it will splash
GeorgeD wrote: Dave - what quantities did yours go off at?
thanks
GeorgeD
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http://davesboat.blogspot.com/

Jones
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Post by Jones »

GeorgeD wrote:Hi Mr Jones,

Thanks for your advice. West Epoxy kits come with "mini pump" dispensers which they say gives the correct ratio. See page 8 of their manual - http://www.wessex-resins.com/pdf/English.pdf
You're welcome :D I visited the site you provided and yes, that looks like the same pump.

Glen L also offered mini-pumps at one time and claimed they were accurate. It turns out, unfortunately, that the pumps cannot accurately reprime with each stroke of heavy plastic resin (epoxy). I already owned my set of scales when I got my hands on a set of pumps... at the least they are convenient for dispensing. Even when they seemed to be priming well, they were miserably inaccurate.

They are no longer offered in the Glen L catalog.
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HouTexBBC
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Post by HouTexBBC »

I have never had that happen to me and I've built 3.5 boats over the last 5 years. I usually don't refrigerate my epoxy (though I have done that once or twice before) and I live in Houston where it is hotter than hell most of the time. I use RAKA's basic epoxy and their slow hardener gives me about 30 minutes even in warm weather. I typically mix in small batches, the maximum being 6 ounces. The mixing pot is a plastic 8 oz "cocktail" cup I get from the grocery store real cheap. I use 1 oz pumps. I actually quit using the pumps made specifically for epoxy and went with ketchup pumps from the restaurant supply store and they work fine. One ounce every time.

For a 6oz mix I spend 3- 4 minutes mixing with a tongue depressor. When spreading straight epoxy I pour it all out on to my plywood, if possible, in figure 8's and then spread it around with the foam roller. The key, as we all know, is to get that stuff out of the pot. For filets, I leave it in the pot longer but with 6oz max, I typically can use it all before it has a chance to kick. If needed I make the fillets kind of quick and ugly-like just to get all the epoxy used up, and then I go back and pretty up the filets. I also have a piece of small ply scrap that I have used for years and what I will do, if I need more time, is spread out my thickened epoxy on that board as thin as I can and then start working on my boat. This gets the stuff out of the pot and keeps it from going crazy.

Dennis

Jones
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Post by Jones »

I suspect those who are having success with pumps are using brands of epoxy that have a ratio more forgiving than the glen-l brand? At 5:1 it's much more critical.
Avoid Haste.

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BruceDow
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Post by BruceDow »

The West System pumps are calibrated at 5:1 and work fine. (except for the West System "Special" Hardener which is 3:1 - be careful to use the right pump)
Bruce.

~~ Do what you love, and love what you do. ~~
~~ To me - only my boat is not yet perfect. Everybody else's is to be admired for I know the path they have walked (Dave Lott, 2010) ~~
Dow's Monaco Project

HouTexBBC
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Post by HouTexBBC »

Jones wrote:I suspect those who are having success with pumps are using brands of epoxy that have a ratio more forgiving than the glen-l brand? At 5:1 it's much more critical.
Can someone tell me the reason for a 5:1 mix ratio vs a 2:1 or whatever? Some brands have a different mix ratio for each hardener so you can't even customize your kick speed. Also, this leads to confusion on the part of the boat builder and sometimes they mix at the wrong ratio and can't understand why the epoxy won't kick. I have heard that story more than once before.

Dennis

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