Best way to preserve open cans of paint on board?

[Scaramanga F25]

Go to an automotive paint store and get smaller cans. There is always air in a partly used paint can.

[Kd9truck]

What ever paint you use, in what ever vessel, read the label to find the thinning agent. Use that thinning agent as a barrier floated on top of that paint. IE: water base paint float a very thin layer of water on top of paint. When it is time to re-use the paint simply stir it in.
Also thining the primer with solvent on steel, boats, I beams, Diamond plate steel will help the paint be absorbed (yes it it a thing) by the steel helping the bond last longer.

Rigger, painter, artist, inventor, sailor, crisis technician 😘

[Northbound44]

Paint manufacturers add nitrogen when packaging paint to remove air from the surface.
I often use argon gas which is heavier than air, by injecting it into the container before closing it, with good results.
Since argon gas, used for welding, is hardly available, we can also use carbon dioxide ( CO2) used with bike tire inflator, as long as it is used only with oil paint. (carbon dioxide dissolves in water). As previously mentioned by others, propane can also be used as blanketing gas since it is also heavier than air.

[Spot]

Originally Posted by Scaramanga F25

Go to an automotive paint store and get smaller cans. There is always air in a partly used paint can.

If the paint is decanted into new containers, label the smaller cans w/ brand, type, part number, solvent type and tape over the label with clear packing tape. A drop of the mixed paint on the lid is or label is a nice touch too...

[hzcruiser]

On top of what've been said, I'm also decanting smaller amounts in old glass jars with screw tops (also using glad wrap under the lid). Even on bigger jobs it reduces the time the can is open.

Before closing the can I also pour in a small amount of compatible thinner.

[Bill O]

Originally Posted by Scaramanga F25

Go to an automotive paint store and get smaller cans. There is always air in a partly used paint can.

+1
Usually we buy 1 gal. containers of paint, etc., then purchase new 1 qt cans to store the leftovers. This reduces the headspace for the paint, varnish so they do not skim over, no paint in the rim, the lids fit perfectly/haven't been pried open and the smaller cans store better.

[chouliha]

For years we have stored paint on the boat in empty qt oil containers. No rust and easy to pour out when a small amount needed. We wash the containers with paint thinner

[BobMc]

Originally Posted by guyrj33

I fill the air space in the can with propane. It’s heavier than air so it displaces the oxygen in the can.

I've been using the propane solution for years on all kinds of paints and varnishes. Never had a problem. Use the propane pencil torch without and open the valve very slowly to "drizzle" (propane is heavier than air) for about 6-10 seconds into the open can. Replace the lid, and it's good to go! The propane replaces the air inside the can and sits atop the paint/varnish/etc, preventing the contents from reacting with the air.

Turning the can upside down helps a little, but over a period of time the contents still reacts with the air. With propane displacing the air, I've kept a small can of Epifanes for over 10 years with no skinning-over.

[StowawayJoe]

I've used the Stop Loss Bags for my varnishes with good results. They might work for paint.
https://www.stoplossbags.com/

[Manateeman]

Ultra pure argon? Ultra? Marketing fluff. Every TIG welder has argon. If it’s not pure, you find out very quickly. Never had unpure argon from my supplier. Find a welder and bring a beer for his manatees.
Propane works fine just have a new small can and lid and keep the salt from making tiny holes you can hardly see. Paint the seams of the paint can. I’ve never stored them upside down but always in a plastic bag in a box in case they leak. Nalgene containers are nice but expensive. Labs and water testing plants toss them. More beer required for bribes.
Some epoxy catalyst is very corrosive if spilled.
Happy trails to you.
Mark and the manatee gang.

[sailing_gal]

Originally Posted by BobMc

I've been using the propane solution for years on all kinds of paints and varnishes. Never had a problem. Use the propane pencil torch without and open the valve very slowly to "drizzle" (propane is heavier than air) for about 6-10 seconds into the open can. Replace the lid, and it's good to go! The propane replaces the air inside the can and sits atop the paint/varnish/etc, preventing the contents from reacting with the air.

Turning the can upside down helps a little, but over a period of time the contents still reacts with the air. With propane displacing the air, I've kept a small can of Epifanes for over 10 years with no skinning-over.

I assume butane would work just as well?

[TeddyDiver]

Originally Posted by Northbound44

Paint manufacturers add nitrogen when packaging paint to remove air from the surface.
I often use argon gas which is heavier than air, by injecting it into the container before closing it, with good results.
Since argon gas, used for welding, is hardly available, we can also use carbon dioxide ( CO2) used with bike tire inflator, as long as it is used only with oil paint. (carbon dioxide dissolves in water). As previously mentioned by others, propane can also be used as blanketing gas since it is also heavier than air.

The weight difference of air and argon is not enough for that to happen, instead you just blow the air out with pressurized argon and close the lid fast. The mole weights are N2 14g/m O2 16g/m and Ar 18g/m. All present in the atmosphere perfectly mixed, even CO2 20g/m.

[Nicholson58]

Nitrogen replacement of the air in the can before closure works. CO2 might also work.

I sometimes open a can by punching two holes 180 apart and pouring out what I need. Reseal with 5200. Never open the lid.

Open cans of most marine paint and Epiphanes will keep longer if you float a layer of mineral spirits on top. Wrap the brush in a bag or Saran and store in the freezer if you are adding layers per day.

Mixed two part anything and the brush can be kept inactive and usable for a couple weeks in the freezer.

[BobMc]

Originally Posted by sailing_gal

I assume butane would work just as well?

Anything that is heavier than air would work as long as it doesn't interact with the contents; the internet indicates that butane is heavier than air., but not sure about the interaction part of the equation.

[s/v Jedi]

Like people wrote: Bloxygen is made for it, no sense trying stuff like propane which may contaminate certain products like epoxy-based paints?

I have a list on Amazon that holds most of what we use; i’s on there: https://www.amazon.com/hz/wishlist/l...?ref_=wl_share