I am curious to know if there are great advantages to either water-based lacquer vs. water-based Urethane. I've been using urethane and am wondering if there is a reason one might switch to using lacquer.
From Paul Snyder, forum technical advisor:
It depends on the properties you need from the finish. If it acts like solvent lacquer, the water-base version should have 100% burn-in between coats, be optically clear, but not the most durable finish. Its good in situations where you want to rub out the finish without witness lines between coats and/or clarity is an issue. If rubbing out the finish isn't important and you want the added scratch, chemical, and heat resistance, then the urethane is the better choice.
Calling a water-based a lacquer or polyurethane is more a marketing ply than it is an aid to classifying the finish. These are coalescing finishes and each product has its own behavior characteristics. There are pluses and minuses to every one of them depending on what you need the coating to do for you. Discuss your uses with the tech supports for each of the manufacturers and let them guide you with your product selection based on what your priorities are and which coatings will meet those needs.
The ability of a coating to "burn in" or "bite" into the coating underneath it is a means of that coating gripping itself to the undercoating in a chemical way, not by mechanical means.
When a coating burns in there is enough solvent action taking place between that coating and what's underneath that the coating softens and/or melts to whatever degree the coating underneath and chemically meshes with that coating.
A mechanical grip is more like the molecules of coating getting "stuck" in the scuffings and sand scratches of the undercoating. The gripping action is mechanical in that sense. Scuffing between coats helps to insure inter-coat adhesion even with materials which you assume might grip chemically (burning themselves in). Those are the two ways to deal with inter-coat adhesion, burning in and mechanical gripping.
Other finishes fuse together to form one continuous film as you apply each coat. These finishes have 100% burn-in. If you sand these finishes back, you will not see witness lines. Shellac, lacquer, and some water-based finishes burn-in between coats.
What happens is the heat causes moisture to get trapped in the finish and makes it blush (turn milky looking). A lot of times the blushing will take care of itself as the moisture escapes from the finish. Nitrocellulose lacquer and shellac also share this problem. If you need a really durable finish for tabletops and the like, conversion varnish is a good choice.