Thick old varnish

[bugbear]

I've got some polyurethane varnish in a tin, fairly old (5 years plus).

It's gone thick and viscous. Is this irreversible partial polymerisation, or can I just thin it a bit with white spirit?

BugBear

 

[ED65]

If it'll thin with white spirit without any gummy bits floating around in it it's probably fine. Even if there are gummy bits it might still be okay after straining, although possibly best to rely on it as only a wipe-on finish at that point.