I had a question about the batch code on the tube of MEKP (fiberglass hardener) and contacted Evercoats tech dept. for the answer. While I was there I figured I ask about painting over Feather Fill being we didn't have a definite answer a while ago when it came up. Slick Sand description mentions you can paint over it without any sealing but there is no yes or no on the subject in the description of Feather fill. I couldn't find a tech sheet so I contacted Evercoat directly. Below is the response to my questions.

I know the batch code is important because I had a polyester primer NOT cure once and the problem led back to the hardener being too old. This batch number can be found right at the bottom of the tube where it is vulcanized together. It is just "stamped" in and very hard to read, but it is there.
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The batch code is interpreted as follows: The first number is the year, 1=2001, 2=2002, and 3=2003. The second two numers are the month: 05 = may, 08=august. The last three are for internal purposes. With MEKP you would not want to use any that is over one year old. For best results in storage it should be stored in a dark, cool place. I would try to get a fresh batch if I were you. If it is over a year, I cannot say it won't work, but it may take longer, or may not cure completely.

For the second question, Feather Fill can be painted over.

Martin, thanks for the info on the batch number. Never knew how to read it.

A few years back I tried to use some fiberglass that would not cure and had to dig it out and clean it up with Lacquer thinner. Now I know why, it was probably 3 or 4 years old. At the time I thought it was too cold since it was around 60 degrees.

Now I know better!