polyurethane

[Jerry Bittner]

Probably been asked a thousand times but if you don't know the answer....

I've finished most of my projects with Minwax polyurethane -- water base.
Application is with an HVLP.

Recently finihsed a coffee table two matchind end tables with plenty of coats of varnish applied.

Yet, last night someone left a water glass on it without a coaster and later when it got noticed, the water already caused a mark in the finish.

First problem is I thought the use of polyurethatne prevented marks like this and secondly, is there a recommended/best way procedure for removing it.

Thanks

[Steve Schoene]

There is a world of difference between oil based polyurethane varnish and waterborne acyrlic varnish, with or without polyurethane. Single part waterborne finishes are more similar to lacquer in their resistance to water and heat than to oil based varnish. Traditional resin oil based varnish will be much more durable than single part waterborne varnishes with polyurethane.

Polyurethane resin in single part finishes is a modifier to the basic resins--mostly alkyd in oil based varnish and acrylic in waterborne finishes. It's principal benefit is abrasion resistence with only modest enhancements to water, heat, and chemical resistence.