Originally Posted by Rcannon
what about an aluminum boat?
painting in the winter..minimum temp?
Due to epoxy being a non-isocyanate cure metal/substrate temp before and after applying epoxy is critical in the winter months because epoxies become dormant faster than 2K primers as the air temp drops.
I would want a 60 degree or warmer substrate during and 4 hours (longer is better) after applying epoxy. Worst case pull it out to warm up in the sun on a cold day but keep in mind epoxies by nature acquire maximum adhesion and corrosion resistance after 7 days @ 70 degrees.
Metal temps inside a building are always 4-10 degrees cooler (depends on the 'metal') than the air temperature and that's assuming the air temp has been consistent. If it has been in a 30 degree barn all night and the air temp happens to now be 65 because you just ran a Reddy Heat heater for 2 hours the metal is still going to be very cold so be very careful.
Also, while not critical on an old jon boat, know that while Al doesn't rust it does produce a film almost instantly once you strip it back down to the bare Al and its exposed to air. On something critical like the restoration of an old Land Rover or MB I would suggest stripping one panel at a time with 80 grit then as soon as possible wash with a waterborne wax and grease remover while drying with a seperate clean towel. Then immediately follow with epoxy. This gives you maximum adhesion on Al.
Please be aware that many nationally know epoxies have been cheapened over the years and just because it was recommended for use on Al or bare metal the last time you used it 1, 5 or 10 years ago doesn't mean that is still true. Ask your paint jobber then verify it through official online data sheets since the jobbers don't always have the latest info.
The last thing you want is to buy is an epoxy that requires etching primer underneath it. Not only is this a waste of time and money when you can find epoxies that still stick to bare metals and Al but acid etching primers (glorified hybrid latex which is why it comes in a plastic jug) can be a disaster long term because over time UV light will re-flow solvents in the paint and primers which need a place to go. These solvents can and will re-flow the latex like etch primer and cause small bubbles in the paint usually on top surfaces. If you carefully pop these bubbles you will see a small amount of rusty water and corroded metal underneath. The solvent reflowed the acid etch releasing water which causes the rust.