Solvents, Diluents,
& Thinners

TRUE SOLVENTS IN COATINGS

Q: What significance does the strength of a solvent have with regard to surface coating applications?

A:  True solvents dissolve something. For instance, water dissolves sugar, salt and thousands of other chemicals. In the case of paints, true solvents dissolve resins, such as epoxies, polyesters, alkyds, etc.

Not all organic liquids (which we refer to generically as "solvents") dissolve all resins. For instance, mineral spirits dissolves some long-oil alkyd resins, but it is incompatible with polyurethanes, epoxies, short-oil alkyds, acrylics and more. Ask a painter if he has ever added mineral spirits to an epoxy or polyurethane? He'll probably tell you that the coating "kicked out" and that his mistake cost him lots of time cleaning out the mess.

Because of their dissolving power, the use of true solvents in a coating formulation is the most effective strategy for lowering the viscosity of a coating.

You are well aware of the saying; "One man's meat is another man's poison." This is equally true when it comes to generic "solvents." Solvent "A" might be a true solvent for Resin "X", but only a diluent for Resin "Y". Similarly, Solvent "B" might be a diluent for Resin "X" but a true solvent for Resin "Y".

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