Is wipe-on just diluted regular- No

Re: Is wipe-on just diluted regular- No

David Weaver

It's interesting that the criticism of the reformulated watco (based on amazon comments) is that it quickly sets up. Well, that's one of the criticisms, there were several.

I'm gathering from your comments (being someone who doesn't brush on poly) that a typical fast-drying poly will start to set up very quickly and become "not runny", unlike what you're seeing?

What happens to viscosity after application

Bill Tindall, E.Tn.

No matter the finish the first thing that happens on the way to "curing" is the solvent begins to quickly evaporate from the thin applied film. When the solvent evaporates the solution viscosity increases. For a solution of a polymer the increase is not linear. Evaporating half the solvent may increase the viscosity 4 or 8, or more times, depending on the shape of the polymer molecule.

Nitrocellulose lacquer is an excellent finish to spray because the increase in viscosity is exceptionally large as solvent evaporates. Runs and sags are minimized. Shellac is difficult to spray because it is not a polymer. Viscosity only slowly increases as solvent evaporates.

On a much longer time scale curing finishes begin to cure, that is, cross link to increase molecular weight, and hence viscosity. After application, "regular" polyurethane will quickly loose an initial amount of solvent from the thin film. (Evaporation will slow as more solvent evaporates and the viscosity of the film increases) . The film will suck up oxygen and, depending on the catalyst, the resin component will begin to cross link at some rate. I don't know how quickly a viscosity increase from this reaction will be observed in the stickiness of the film. But you are correct that it will vary, maybe a lot, from this varnish to that.

Varnish companies know how to manipulate all these variables to reach a target for the properties of the varnish. One thing we can be sure of is that these properties will differ company to company and that over time they will change, annoyingly, for the same company.

another difference observed

Bill Tindall, E.Tn.

As the "wipe-on" solvent evaporated slowly in my cool shop it did not skim over from cross-link curing. I suspect the curing rate of this varnish is slower than regular varnish. Slowing the oxidative cure will slow the rate as which the varnish gets sticky when wiping it on.

Wipe-On % solids

Bill Tindall, E.Tn.

Minwax Wipe-On determined to be about 40% solids( I would need a more accurate scale to know if it is 40 or 41 or 39. I don't know what regular is, probably 40-45%. All the data is consistent with the conclusion that wipe-on is not simply regular diluted enough to slow drying enough to enable wipe-on application.

It does not make business sense to sell wipe-on as simply a diluted version of regular. Finish companies know enough about the properties of their ingredients to be able to formulate optimally for an application. So why wouldn't they?

That is not to say that regular can not be diluted enough to be applied with a rag. I don't know, never tired it. I do know that adding enough linseed oil to make it a wipe-on will substantially alter its film properties.

Re: Wipe-On % solids

David Weaver

Interesting that you'd find that number. One of their MSDS sheets (that doesn't show a range) suggested much closer to 30.

From what you mention, much makes sense. I wiped on the minwax wipe on, it probably dries slower (which is no issue to me) and never had any issue with it setting up or globbing, which would be a real pain. It makes sense that it would cure more slowly, but that in a brush on product, slow curing and slow setup would lead to unexpected sags that weren't there when you walked away from brushing on a coat.