Ecothermic Epoxy Heat

[ccx2]

Hey Guys, Im doing some large fillets, 2" radius, some of the fillet in an area ecothermic heated and of course got real hot and hard quick, does this effect the bond or strength in any way? I couldnt find anything in West Systems info guide. Should i keep worrying ? Thanks

[ccx2]

Well, i just got back from the garage and answered my own question. It has cooled and has cracks in it, time to break out the grinder and have a do over, guess ill have to do the fillets in two steps, one over top the other to a 2 1/2" radius like the plans call for. Sucks to be me sometimes::mad::o:D

[ccx2]

I wonder what im doing wrong? i know others have done fillets that big without problems. No one needs really to answer these questions, ill continue this thread by myself, i often answer myself when im talking to myself, i dont know if im confused or not.:)

[Thorne]

I take it that this is a rapid-cure epoxy of some sort? Any chance of waiting for it to cool a bit before glopping it on?

[ccx2]

I take it that this is a rapid-cure epoxy of some sort? Any chance of waiting for it to cool a bit before glopping it on?
No , just West system with slow hardner. When it get hot its kicking off and wont cool untill its hard.

[AJZimm]

Also, what are you using for filler?

I have done some fairly large radius fillets and filler blocks using wood flour and/or fine sawdust as filler. Had no problems cracking even though the epoxy got pretty hot on one block that I recall. I suspect the sawdust compresses to take up internal expansion in the epoxy as it heats up and hardens

[ccx2]

It won't cool once it has warmed up, not in any way that will help here. When it gets hot, its about to "go".

I've done 2" radius fillets and not had any heat problems. The epoxy isn't really that thick on a 2" radius fillet - we worked this out a while back IIRC,

Yep, found it...

http://i240.photobucket.com/albums/ff112/igatenby/iansecond/epoxy.jpg

Which epoxy are you using, which hardener?
West System with slow hardener. Yes we/you did work it out but i couldnt find the thread. I think maybe what happened was i put down a layer of goop that wasnt thick enough to complete the fillet and mixed more and applied over the previous layer and they were setting at a different rate, the second layer trapped the heat in the first and goofed up the cure in both maybe.

[TimmS]

I've never heard of epoxy cracking.....what filler are you using? what is your shop/outdoor air temp? are you working in the sun?

[TimmS]

sorry alex...same idea at the same time :)

[JimConlin]

If the bog is going off too fast, all you can do is mix smaller batches, lay it on in two layers and have a helper mix it. For that much bog, I use a mechanical mixer- try less than a quart of bog in a 2-1/2 qt. pot.

[SchoonerRat]

If you mix a little bit of milled fibers into the glop it might help hold it together.

[Todd Bradshaw]

If you are using a microballoon-based filler, understand that the balloons are good insulators and trap heat. Other fillers (like wood flour) will also insulate to some extent, but not as much as balloon-based fillers will.

[S B]

This might seem odd, coming from me, but I have had experience with thermosetting resins. Back in the good old days,before things got user friendly, we used to add catalyst with an eye dropper. One drop too many and the resin could catch fire, I'm not kidding. Your cracking problem might be of a similar nature. The slow hardner you mentioned works fine for the usual thickness of fillet but the dosage may be too strong for the thicker application. You might try cutting the amount you use.

[Bill Huson]

Yep. I've had heat runaway with polyester and epoxy resins. Had a batch of poly ignite once.

No location in your header tag, but I suspect you live in a warm climate. The kick time for resin is not a linear curve with air temp. Slow 206 WEST mix will look at you at 60 deg F, go off as advertised at 70 deg F, and go batpoop crazy fast at 80 deg F.

Solutions: Wait until the cool, cool evening to do the fillets. Or switch to 209 "tropical" hardener. Or as had been suggested, do the fillets in thinner layers. And as has been mentioned, micro balloons and/or sawdust do seem to bend instead of break under a runaway high heat situation. I seem to recall the WEST guidelines warn against doing a second mix on top of a short mix. Apparently the heat produced by Mix #1 spanks Mix #2 into premature exothermation. :D

[Todd Bradshaw]

Do not reduce the hardener amount for epoxy resin! Polyester resin is a totally different deal and you adjust hardener amounts for different ambient temps and thicknesses. If you try the same with epoxy, you will end up with resin that never cures completely and a hell of a mess to clean up.

[S B]

Do not reduce the hardener amount for epoxy resin! Polyester resin is a totally different deal and you adjust hardener amounts for different ambient temps and thicknesses. If you try the same with epoxy, you will end up with resin that never cures completely and a hell of a mess to clean up.
Fill me in here, fast hardener and slow hardener for epoxy are different chemicals? as opposed to different strengths of the same one.

[JimConlin]

Fill me in here, fast hardener and slow hardener for epoxy are different chemicals? as opposed to different strengths of the same one.

Yes.

In either case, they MUST me mixed with the epoxy in a proper ratio. The resin molecules and the hardener molecules need to pair up in precise ratios. Think of water- two hydrogens and an oxygen.
So, in working with a manufacturer's epoxy system you have to observe the prescribed mix ratios.
It's useful to understand that when the reaction of epoxy resin and hardener happens, heat is produced and that the reaction between epoxy resin and hardener is faster at higher temperatures. Putting these two together the 'chain reaction' of the epoxy system is something that you need to control.

What you CAN control is:
- which hardener you use. For example, West System has four for their 105 resin- fast, slow, slower and UV-tolerant. Some other systems have a broader range.
- The temperature of your resin and hardener. If they're cool, they're harder to measure and to mix and the mustard pumps burp, but they won't 'go off' quite as quickly.
- The temperature after mixing. Putting your mix in a flat pan, maybe even on a cold water bath, will slow it down.
- ambient temperature- Cool the shop if your epoxy is too eager.
- time in the pot. If you use small batches and get 'em applied quickly, you have a better chance of staying ahead of it.
- You might not want to control with it, but be aware that insulative filler materials like microballoons are good insulators and don't allow the heat of the epoxy reaction to escape as well. The captive heat accelerates the reaction. A pint of microballoon bog has a very short life. It doesn't take long for a hot solid mass to form in its middle. The solution is smaller batches.

I'm sure that this harangue is incomplete, but I tried.

[David G]

Yes.

In either case, they MUST me mixed with the epoxy in a proper ratio. The resin molecules and the hardener molecules need to pair up in precise ratios. Think of water- two hydrogens and an oxygen.
So, in working with a manufacturer's epoxy system you have to observe the prescribed mix ratios.
It's useful to understand that when the reaction of epoxy resin and hardener happens, heat is produced and that the reaction between epoxy resin and hardener is faster at higher temperatures. Putting these two together the 'chain reaction' of the epoxy system is something that you need to control.

What you CAN control is:
- which hardener you use. For example, West System has four for their 105 resin- fast, slow, slower and UV-tolerant. Some other systems have a broader range.
- The temperature of your resin and hardener. If they're cool, they're harder to measure and to mix and the mustard pumps burp, but they won't 'go off' quite as quickly.
- ambient temperature.
- time. If you use small batches and get 'em applied quickly, you have a better chance of staying ahead of it.
- You might not want to control with it, but be aware that insulative filler materials like microballoons are good insulators and don't allow the heat of the epoxy reaction to escape as well. The captive heat accelerates the reaction. A pint of microballoon bog has a very short life. It doesn't take long for a hot solid mass to form in its middle. The solution is smaller batches.

I'm sure that this harangue is incomplete, but I tried.

I would add one bit about mixing big batches. It's good to have the resin & hardener warm enough to flow thru the pumps easy, and mix easy. After that, though, you want the maximum working time possible, which means keeping your goop cool.

One way to achieve this is to spread it out. Rather than keeping it massed together in a cup or bucket, pour it into a paint roller tray. I use the disposable liners, and just toss 'em when I'm done. If the weather's warm, or I've got a complex glueup to do, I'll put a little cold water - or even ice - in the metal tray, and float the plastic disposable liner in it. It makes a huge difference. As mentioned above, the speed of cure does not increase in a linear fashion with the ambient temperature, but rather - IIRC - in a hyperbolic curve. Cooling it off, REALLY slows the process down.

Oh, and I realize it was probably just a typo... but to avoid confusion, the word is exothermic.


"Many a man who falls in love with a dimple makes the mistake of marrying the whole girl" -- Evan Esar

[S B]

Thanks for the replys, epoxy isn't a catalyst produced reaction, hardener is the other half of the compound, understood.

[pipefitter]

Use a larger container to mix it in. If you don't let it get too deep, it won't get hot. I use an aluminum plasterer's hawk for most of my mud work. The aluminum draws the heat out of it quite well. When working from a container, I will still stow some of the mix on the hawk and just round it up with the putty knife and add it to the pot when I need it. It ends up buying me about 20 minutes extra time.