Thread: unexpected violent reaction in epoxy, anyone seen this before?

I've spent quite a bit of time in boatyards and seen this event many times. I saw a yacht burn to the ground on the hard after a big batch (4 litres) went bad. It has also happened to myself on the odd occasion. The ambient temperature has an effect on the reaction as does the shape of the container. I find that using a large diameter bowl helps stop the accumulated heat and thus slowing the reaction. Once the reaction starts it goes very fast and for the unsuspecting can have disastrous results. On warmer days over 30 degrees I reduce the amount of catalyst too. For small batches, plastic ice cream containers work well.

steve

I experience this when it was hot - when epoxy sets up, it heats up, this accelerates the reaction further, and more heat is generated - this is like a chain reaction.

On the other hand, sometime I gently heat up the epoxy to make it set quicker.

Happened to me as well when I left some Techniglue in a nice lump. Just a runaway chemical reaction.

I have seen this quite often. Seems to be narrow neck containers is the common denominator. Never had a problem with large plastic ice cream containers.

You shouldn't reduce the amount of hardener. It's not like the hardener is a catalyst (as with polyester), the hardener is a critical part of the set epoxy.

Think of it like cement; too little water, and you still have dry cement powder; too much water, and you've reduced the strength of the finished product.

Not enough hardener and it might reach the 'nup, I'm never going properly hard' stage because it runs out of the appropriate stuff to chemically combine with.

Originally Posted by Master Splinter

You shouldn't reduce the amount of hardener. It's not like the hardener is a catalyst (as with polyester), the hardener is a critical part of the set epoxy.

Think of it like cement; too little water, and you still have dry cement powder; too much water, and you've reduced the strength of the finished product.

Not enough hardener and it might reach the 'nup, I'm never going properly hard' stage because it runs out of the appropriate stuff to chemically combine with.

You're right, my mind slipped from epoxy into polyester mode. Brain is getting old

Originally Posted by rustynail

I have seen this quite often. Seems to be narrow neck containers is the common denominator. Never had a problem with large plastic ice cream containers.

My incident wasn't in any container, just a blob of Techniglue on a piece of scrap MDF

Originally Posted by elanjacobs

My incident wasn't in any container, just a blob of Techniglue on a piece of scrap MDF

So much for my theory.

Thanks for all the replies. I was a bit surprised to see so many. Seems like this happens often enough which makes me wonder why there is no warning about it. Also the second batch didn't appear to have the same issue and it was in a similarly sized cup so.....weird. I guess in future i will try to keep the lot in a shallow container.

I find paper plates good to mix epoxy on to keep the pool of product as shallow as possable. I also use a wood stirring stick and applicator never anything synthetic. The larger the batch the hotter it gets. I never bin the plate before it has gone hard and cooled either.
Regards
John

This is entirely normal, to be expected and frequently warned against.

I have had accelerated curing in batches as little as 30ml.

I have never has a situation where the epoxy has got too hot to handle, started smoking or burnt...because I was aware of the issue from the get go....but I have had a couple of small batches go off or go lumpy in minutes where I would expect it to remain workable for a good half an hour or more.

The word is.....if you are mixing any significant volume of epoxy.....or many other two part glues or resins.....by all means measure and mix them in an errect container.....but as soon as the mixing is done, get the material poured out into something flat and get it spread out so it can disipate the heat.

Many of the boaties mix up and just dump the batch straight on the job and get it spread out.....I generally use small roller trays.

AND of course..with epoxy it pays to mix as little as practical in one batch.

if you must keep the mixed epoxy in an upright container for any sort of time...keep sturing.

I know some people will howel me down...but it seems West is more prone to this than Boat Coat.....my understanding is that boat coat is partly pre-reacted, where west is not.


as for why one part of the mix goes off faster than another.....well the reasons may vary......if the top is going off like a disk..maybe the outside air is hotter than the mix.....if it goes off in a lump in the middle....well its hottest in the centre.....there may also be an inadequate mix, so some parts may have more concentration of reaction.

Perhaps the mix proportions are a bit off.....there may be a tendancy for surpluss parts to not combine redily with the mix if outside ideal proportions this may mess with things.

I don't know about West, but some epoxies are influenced considerably by moisture as well as temperature.....the brush may either bring or take moisture and heat to or from the pot.


Epoxy is truly wonderfull stuff.....but you need to be fussy to get best results and safety.

cheers

It shouldn't be unexpected as it is well known to the manufacturer who offers advice in their technical data. Quotes from West System "Epoxy Safety" brochure available at http://www.westsystem.com.au/west_sy...s/epoxy_safety The highlights in red show some of the reasons for your experience.

"Care should be taken when dispensing and mixing. Do not attempt to control the cure time by altering the hardener ratio. Contact ATL Composites for specific information."

Uncontrolled curing and burning of epoxy

"The chemical reaction that cures mixed epoxy is exothermic , or heat generating. If left to cure in a contained mass, such as in a mixing pot, it can generate enough heat to melt plastic, burn your skin or ignite surrounding combustible materials. The larger or thicker the epoxy mass, the more heat generated. A 100-gram mass of mixed epoxy can reach 400°F.

To prevent heat buildup, transfer epoxy from the mixing pot to a roller pan or other wide, shallow container. Fill large cavities with epoxy in multiple layers rather than in a single, thick layer. Heat build up and uncontrolled curing are unlikely in typical bonding and coating jobs, because spreading the epoxy into thinner layers dissipates heat.

Mixed resin and hardener become hot and frothy as they thermally decompose, generating toxic vapors. These include carbon monoxide, oxides of nitrogen, ammonia, and possibly some aldehydes. Cured epoxy can emit similar vapors if you heat it too much. This can happen when you use a flame to release epoxy-mounted hardware. To reduce this risk, use just enough heat to release the hardware. Only as a last resort should you use a flame to burn epoxy from hardware. If you must do so, work in a well-ventilated area.

While leftover mixed epoxy cures, set the container aside where you can monitor it. Use a fan to disperse vapors and direct them away. Air purifying respirators may not be effective against these vapors.

Spontaneous combustion is a danger when hardeners are mixed with sawdust, wood chips, or other cellulosic mterials. When hardener is spilled onto or mixed with sawdust, the air and moisture react with the amine to
generate heat. If the heat is not dissipated quickly enough, it can ignite the sawdust. Do not use sawdust or other cellulosic materials to absorb a hardener spill.

Likewise, do not pour unused hardener into a trash can with sawdust or other cellulosic materials.
West SYSTEM epoxy resins and hardeners are classified non-flammable, because their flash points are greater than 200°F and they evaporate slowly. Furnaces, wood stoves and other heat sources do not pose a serious fire hazard in the
presence of epoxy vapors.”