What Is the Difference Between the Terms “Thinners” And “Solvents”?

Often referred interchangeably, the terms “thinners” and “solvents” for all practical purposes mean the same thing to most of the painters. There is distinction, however, and it can be of extreme importance. Most thinner can be used as solvents, but not all solvents can be used as thinners. Coating manufactures will specify particular thinners to be used with their materials, some of which are blends of different solvents. The manufacturer’s recommended thinner must always be used in the quantities recommended to thin coatings. Many painting contractors will buy inexpensive solvents that are particularly adapted for cleaning equipment. If a solvent is not recommended by the coating components manufacturers is used to thin the paint, it can cause separation of components, coagulation, too fast or too slow drawing, changes in flow characteristics, lifting of previous coats, and a host of other undesirable conditions. Cleaning solvents must always be kept segregated from the coating materials and thinners.

The different types of thinners in common use and the type of coating materials for which they are typically used are:

   Mineral spirits	   Oils or alkydes
   Aromatics (benzene, xylol, toluol)	       Coal tar epoxys, alkydes, chlorinated rubbers
   Ketones (MEK, MIBK)	   Vinyls, epoxies, urethanes
   Alcohols (isopropyl)	   Phenolics, inorganic zincs
   Water	   Acrylics, some inorganic zincs

The solvents of thinners used with most coatings produce vapours that are heavier than air, as a result, will collect in tank bottoms ot comfined locations unless means are employed to disperse them. The exception, of course, is water used as a thinner in some inorganic zinc and acrylic coatings. The ketones have the lowest flash point; however, a connection of any otganic solvent in the right proportions with the air can creat an explosive combination.