Flame Master (ProSeal?) shelf life data point

Back in 2009 I purchased two tubes of FlameMaster sealant from Vans. I was going to use this for sealing the firewall of my Rocket project. As it turned out I ended up using some left over ProSeal an acquaintance had and both tubes went unused.

I noticed that the plastic bag the cartridges come in states that the shelf life is 6 months but may be extended by refrigeration. I thought I might as well put them into the freezer - my thought was that this should extend the shelf life even further.

And there they sat until last Saturday when I pulled them out of the back of the freezer where they had been for 5 years and decided to see if the material would still cure. Once both tubes had come up to room temperature I mixed them according to the instructions.

Lo and behold in 24 hours the contents of both cartridges had set up tack free - I had forgotten how much that stuff stinks - and to all appearances it has now cured as I would have expected fresh material to. Not that I would have used it for sealing tanks but it is an interesting data point.

So I think the statement about refrigeration prolonging the shelf life is true, and even more so for freezing!

This makes me wonder... what happens once it actually DOES get past the shelf life? Will it not cure? Not stick? Just not guaranteed to be as good? I have to wonder.

If I recall correctly, since it has been many years, old sealant can loose its intended properties; adhesive strength, solvent resistance, shear strength, etc.

Out of shelve life date sealant can be tested (tack free time, shear strength, viscosity, hardness) to extend the shelve life, but I have never seen the date extended more than 6 months.

And yes, it is accepted practice that sealant shelve life can be extended by lower storage temperatures.

Don't throw out too fast

I actually did a little informal test on some old (stored at room temp at the back of the shelve at least two years past exp. date) Proseal. Bonded two sets of aluminum sheets together. One with new ProSeal and one with the old stuff. After a day or so the new stuff had cured as advertised but the old stuff was maybe half as cured. Threw the project aside and forgot about it till a few weeks later when I was cleaning up the shop. I found the old Proseal just as hard as the new and just as strong. ( Informal separation test). I'm sure eventually it won't bond as the solvents dry out but for none sealing jobs it might just be a case of extended curing times. Wouldn't use anything but fresh stuff on tanks.

NYTOM said:

I actually did a little informal test on some old (stored at room temp at the back of the shelve at least two years past exp. date) Proseal. Bonded two sets of aluminum sheets together. One with new ProSeal and one with the old stuff. After a day or so the new stuff had cured as advertised but the old stuff was maybe half as cured. Threw the project aside and forgot about it till a few weeks later when I was cleaning up the shop. I found the old Proseal just as hard as the new and just as strong. ( Informal separation test). I'm sure eventually it won't bond as the solvents dry out but for none sealing jobs it might just be a case of extended curing times. Wouldn't use anything but fresh stuff on tanks.

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Sounds like the same results that I have seen 25-years ago. At one time, I would have said it may cure but it may not. The amount of time you wait can be a lot longer with out of date material. Under no circumstances would I use out of date material on fuel tanks.