Mr Chemist..epoxy/cold weather

[Greg H]

I know there was a post recently on using epoxy in cold weather, but my computer doesn't get on well with the search thingie...so..
Do I remember correctly that epoxy only has to be kept warm until it begins to kick and then it will cure regardless of the temp? Will it be as strong?
-------------Thanks, Greg

[thechemist]

This is not a trivial question, and there is no general answer which is the same for all products.

Whether an epoxy resin will react with its curing agent, and how, depends on the particular molecular structure of the curing agent, meaning the particular energy-level environment in which the amine hydrogens are arranged. This determines the lowest temperature at which the product will cure in the intended manner, by amines reacting with epoxide groups to give the intended result, a beta-amino alcohol, or beta-hydroxy-amine, depending on which name you prefer for the cured resin.

Acrylates are also used in mixtures with epoxides, as they react faster with some of the amines, but acrylates being esters give increased moisture-sensitivity to the result. Everything is a trade-off.

If the epoxide and amine do not react in a certain time frame, there is a second competing side reaction in which epoxide groups condense with each other, and that goes slowly in the cold when the first reaction dies. Thus, if it doesn't cure correctly at first, then sitting in the cold for a long time it tends to cure incorrectly, and then there are no epoxides left to react with all these amines if and when it warms up again, and it will thus never cure correctly.

There are other curing reactions of epoxides such as with mercaptan curing agents that have very low threshold energy levels, like minus twenty centigrade or less. Mercaptans react by forming the mercaptide ion, which is a VERY reactive species. Epoxide-amine reactions tend to have threshold temperatures in the range of plus ten to minus ten degrees centigrade.

There are accelerators ["catalysts"] that can help things to cure better at lower temperatures, so as to avoid incorrect curing and which facilitate correct curing. Some formulators use these things, others buy pre-formulated products from industrial suppliers.

There are steric effects, so-named because certain molecular shapes react more readily than others, due to the shape of the molecules and catalysts. These vary with the formulation.

The bottom line is that you will need to rely on what a particular manufacturer says about their products......there is no valid blanket statement in this regard.

[Greg H]

Err um, it comes down to rtfm.
Thankyou, Greg

A quick call to MAS later:

Using Low viscosity resin and med. hardener.
The first 24hr are the most critical, in this case the epoxy needs to remain above 40deg.f.
Once it is set, it will continue to cure and the strenght won't be affected if the temp briefly falls below 40f. Avoid extremes if possible by insulating the work in some fashion.

! If using a heat source, make sure the wood is heated before the epoxy is applied to avoid problems with out gassing!
MAS-1-888-627-3769

[RGM]

I considered chemist's final statement in his post "there is no valid blanket statement in this regard", and I came up with a blanket statement. Use an electric blanket ( or two) to pre-heat your work and regulate the temperature while things are curing. Done it lots of times, works great once you get set-up. Use visqueen or tarps to protect the electric blankets(s) from the epoxy. If outside wrap the whole mess in tarps or visqueen to keep the weather out. I've even wrapped the whole thing in house insulation when necessary to control heat. Good luck.

[thechemist]

There ya go.