Solvent vs. Thinner

[kmealy]

Solvents dissolve things.  Thinners thin things.

 

Edited December 3, 2024 by kmealy

[John Morris]

Hey Keith, so we have a table of solvents. But what about the "thinners"? I noticed they used Thinners plural, what types of thinners are there?

Also what's not clear to me right now, "Solvents dissolve cured finishes", does that mean we should avoid solvents for thinning, is that the message here? Thanks!

[kmealy]

Well the same chemical can be used for different things -- for example, mineral spirits or naphtha will dissolve wax, but it can also be used as a thinner for oils and oil-based varnishes.    Acetone will dissolve lacquer, but it's also a main ingredient in most lacquer thinners.  Lacquer thinners are a mix of multiple solvents, co-solvents, and thinners.  The exact mix depends on what it's intended to do and economics.   If you want to know, search on "<brand> lacquer thinner SDS"

 

Flexner explains three types of finishes as spaghetti, tinker toys and soccer balls

* Spaghetti - when the solvent evaporates away, the finish becomes hard.  Add more solvent later and it softens the finish.  This is why shellac and lacquer create one coat as the solvent in the later coats dissolve some of the earlier coats and make one layer of many coats.  Putting cooked spaghetti noodles back in boiling water will soften them back up and make them edible.
* Tinker toys - oils and oil-based varnishes.  The thinners evaporate away (AKA flashing off) an the remaining parts combine with oxygen to make long polymer chains.  Adding subsequent coats do nothing to the prior coats so there are multiple  layers.  If you've ever sanded varnish you can see the layers if you sand thru an upper coat

*  Soccer balls -- water-borne finishes.  These are large molecules and the thinner "softens" their edges.  When the thinner evaporates away, the edges bond to each other and become one film.  Water is one thinner, but there are others that do the softening.

 

As an aside, when I was doing upholstery cleaning, there was a bit of chemistry involved.   The majority of cleaners were of one of two types, polar and non-polar.  Polar solvents have a + and a - chemical side.  Most stains I encountered - general soiling, food, body oils, body fluids needed this type.  Non-polar have neutral charges and were generally what's needed  for things like oil, grease, etc.  In addition, I had cleaners that added oxygen those that took oxygen.  Those that added were good for  blood stains and most food dyes.  Those that took oxygen were needed for red food dye.  And most of these also had surfactant or emulsifier chemicals like a dish or laundry detergent that dissolved whatever was in there.

[HandyDan]

I am surprised how well mineral spirits work to dissolve self-stick label adhesives.  I use to use brake cleaner but that ate into some plastics.  Now I reach for the spirits first.

[kmealy]

Yes, since poly is a tinker toy and lacquer is a spaghetti, you can use mineral spirits  to clean furniture.  But to follow the upholstery example, Dawn and water also works very well for most dirt (like food and body oils).   I used it often to clean kitchen cabinets before touch up and refreshing with new lacquer.