UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - What causes this in polyurethane varnish?

duncanlowe · 31st Jul 2020, 9:57 pm

Something I learned via a distance learning course many years ago. Paint doesn't dry, it cures. It's not simply about the solvent evaporating whatever solvent that may be. Someone has already said this. The oils in the paint oxidise.The same effect can be seen with cooking oil on pans, cookers and extractors.

I'm not sure whether polyurethane varnish works in the same way, but I'd expect it does. So recoating would need to be done either before the first coat has started to cure, or after it has cured well.

31st Jul 2020, 9:57 pm	#31
duncanlowe Nonode Join Date: Jan 2016 Location: Stafford, Staffs. UK. Posts: 2,532	Re: What causes this in polyurethane varnish? Something I learned via a distance learning course many years ago. Paint doesn't dry, it cures. It's not simply about the solvent evaporating whatever solvent that may be. Someone has already said this. The oils in the paint oxidise.The same effect can be seen with cooking oil on pans, cookers and extractors. I'm not sure whether polyurethane varnish works in the same way, but I'd expect it does. So recoating would need to be done either before the first coat has started to cure, or after it has cured well.