Mercury epoxy NOT clear

[Haynie]

Not a happy camper right now. I mixed up a large amount of 15 minute Mercury Epoxy which was bought last winter. Both bottles were clear and when I have used it in the past it cured clear with no yellowing. I never mixed this much up before though. I needed to plug some knot holes in some flat work I am doing and wanted it to be clear, so I mixed it all up because I was going to need it all.

It was clear when I mixed it. Clear when I started pouring it. I poured two boards and went to grab the next two. Total time 6 minutes from mix to pour to getting back with the next boards. I had a timer running. This is what it looked like. I tried to pour a little into another cup to see if it would cure clear. It never got out of the cup as you can see, and it was freaking hot!

We will see what things look like in the morning, but as of now the board with the largest knot looks like crap. I have enough wood to replace this board thank goodness.

I opened my mercury 30 minute epoxy box which I have never opened and the hardener is pee yellow. Looks like I am in the market for some different epoxy.

 

[Russianwolf]

Shelf life.

We all like the idea of buying in bulk and using it as we need. But a lot of these products have a shelf life and change chemically as they near it.

I myself have a half gallon solid block of PR.

 

[Haynie]

So epoxy shelf life is like 8 months?

 

[edstreet]

most all epoxy will tone with age. There are a few that does not.

 

[Russianwolf]

So epoxy shelf life is like 8 months?

May be even less. I found a note mentioning that the hardeners will yellow with age (but it doesn't effect strength).

Here is another note from West Systems FAQ

PROBLEM: Epoxy became very hot and cured too quickly.
POSSIBLE CAUSES & SOLUTIONS:

Batch too large.

Mix smaller patches.
Transfer the mixture to a container with more surface area immediately after mixing.
See Understanding Cure Time and Dispensing and Mixing in the User Manual.

Temperature too warm for the hardener.

Use 206 Slow or 209 Extra Slow Hardener in very warm weather.

Application too thick.

Apply thick areas of fill in several thin layers.

 

[Haynie]

Thanks Mike.

Wish West Systems wasn't so expensive. I used it once on some boat repairs and it was sweet stuff.

 

[Russianwolf]

expensive yes. worth it yes.

The clear cast resin blanks that I make (Dichroics, Opal FX and the new Prism FX) all use West Systems 105/207. I've run into so few problems using it that the lack of waste is worth the extra up front cost.

Some of the things I play with melt from the chemicals in PR, and I have yet to successfully mix a batch of Alumilite that didn't turn pure white (all on me I'm sure, but its frustrating). The Epoxy gives me a longer open time and creates less heat as it cures (some things don't like the heat from PR either).

 

[Ed McDonnell]

If you want your patches on your flatboard to stay clear and not yellow over time, then you probably shouldn't be using structural epoxy. At a minimum, keep your epoxy boards out of the heat / sun (UV).

More heat and sun = faster yellow. "Freakin" hot in the pot = hard and yellow in the pot. Of course, I'm not telling you anything you don't already know now. :biggrin:

There are clear uv resistant casting epoxies that will resist yellowing, but resisting yellowing isn't the same as "not" yellowing. The uv resistant bar top coatings aren't too expensive. Clear uv resistant epoxy for thick casting (e.g. epoxacast 690) are a bit on the pricey side.

Ed

 

[Haynie]

Thanks Ed. I thought the waxed cup I mixed it in was going to burst into flames. The wax did melt.

I did not know about the yellowing over time thing. I will look into the stuff you mentioned.

 

[Haynie]

Mike, West Systems assumes you use a LOT of epoxy. I would never be able to use it in time.

 

[Russianwolf]

Mike, West Systems assumes you use a LOT of epoxy. I would never be able to use it in time.

True, the smallest is a about a quart and a half, but they do sell repair kits with small packets of epoxy if you only need it occasionally. I don't think they do the 207 clear hardener in the repair kits though.

 

[alparent]

get the resin in bulk and the hardner in a more time manageble size

 

[Haynie]

So, the resin does not go bad? I assumed, since both the resin and the hardener of the 15 minute epoxy were clear, that both had gone bad.

 

[alparent]

I've had harder turn yellow, but never resin. (Yet!)
But this is just my very limited experiance.
Maybe resin will also change color over time but I just used it all before it get to that?
I have 5 min resins that are a couple years old. The hardner is yellow but the resin is clear.

Maybe other with more experiance can shime in?

 

[MrGrump42]

First a quick note about me. I've been turning pens for about 4 years now and have been a chemist for 27. Yellowing in epoxies have three sources.

The first is from the hardener. Many are straw color to a brownish yellow. If the mix ratio is fairly high, the color gets diluted. This also isn't an issue if tinting.

The second source is from the heat generated by the cure. Epoxies generate heat when curing and the faster the cure the higher the heat. Casting resins will have a longer pot life than an adhesive type. For the Smooth-On EpoxACast 690 resin, I would choose the 103 Slow Hardener for best clarity. Also only mix up minimal amounts. the larger the mass, the faster it will go as well.

The third source is from UV exposure. To make the resin UV-resistant (not proof), additives are used to slow the process down which are expensive even in the small quantities required.

 

[LanceD]

If epoxy is left in the mixing cup the catalytic reaction is much, much quicker and you will have a solid mass just as in your cup in a matter of minutes.

To keep that from happening, after mixing pour your epoxy on a flat surface covered with aluminum foil and spread iy out thin. You'll find that you will increase the pot life by a considerable amount.