Paint Thinner vs. Mineral Spirits
Issue: Issue 109
Posted Date: 10/19/2004
One of the more interesting threads I've read in a while, not because of the wealth of good information and opinion, but because it was so astonishingly misguided and confused, started with someone asking: "I've been told on a number of occasions that paint thinner and mineral spirits are the same thing. Is that really the case? If they really are the same and interchangeable, why is there such a big difference in the price?"
What followed was a hash of illogic and disagreement, going back and forth between just a couple of people, followed, at last, by some solid information from a new party. Here's a sampling, though please don't assume what you read here is all true:
"paint thinner" is a purer distillation. It is formulated to have less residues and contaminates [sic] and to dry faster. The best paint thinners are VM&P Naphtha. Even pedestrian naphtha is not suitable for thinning paint."
"I don't know about other areas but all the home centers here sell a gallon of paint thinner for about half the price of a gallon of 100% mineral spirits. If paint thinner is supposed to be refined further than mineral spirits, why does it cost less?"
"Here's my take: 100% mineral spirits is more refined, therefore it costs more. "Odorless" versions cost even more. "Paint thinner" is less-refined, because if you're thinning paint, who cares if there is some stray residues in the thinner?"
"I just did a search in hopes of educating myself and found this - www.newparks.com/solvents.html - It leads one to believe that "paint thinner" is now a generic term used to describe the lowest grade of petroleum distillate solvent. & When thinning paint, apparently any old stuff will do& So in the end, I reverse my decision. No, don't use what you have on hand. "Paint thinner" is not suitable for thinning paint."
"To my way of thinking, you can use naphtha, mineral spirits or paint thinner in a 3-part brew with equally successful results. I thought the thinner was just the carrying agent for these wipe on finishes. All are volatile and flash off anyway. It's just a matter of how fast."
"Does it really make a difference? Yeah, I know it does. Sometimes I have to use a blacklight to see it, and sometimes we are talking about the difference between finish structures that will only last a hundred years as opposed to two hundred years."
Finally, like a breath of fresh air, someone new chimed in with:
"All these things are distillation fractions of petroleum. By and large they are the aliphatic component of petroleum. Naptha is largely pentane and hexane while mineral spirits is a mix of somewhat larger molecules, probably mostly octane. By far the main difference among them will be boiling point (how fast they evaporate, flash point). In addition they will differ in minor components that will contribute more or less odor. None of these constituents should have any effect on the curing chemistry of a finish.
Because they are distillation fractions they are all 100% volatile. How fast they evaporate will differ, which in turn will effect the flash point: -40 C for naptha and 0 C for mineral spirits. Mineral spirits evaporates slower than naptha. "Paint thinner" could be naptha or mineral spirits (or any of a number of other common names for these fractions-ligroin, petroleum ether, etc). So paint thinner may evaporate the same as, or faster, than mineral spirits depending on what the distiller decided to put in it. If it is cheaper it probably means that the boiling range of its constituents are less tightly controlled which should be of little concern in many finishing applications.
Personally I use whatever is the cheapest. I would use naptha if it was cold and I needed to get something dry faster but its low flash point makes it a more flammable choice."
For the record, as your loyal scribe and resident finishing expert, I will tell you that the paragraph above, contributed by Bill Tindall, is the one part of this thread that is completely correct.