Chemical paint removers work only on certain types of finishes, and when multiple types of finishes may have been used on any particular surface, trial and error testing is typical to determine the best stripper for each application. Two basic categories of chemical paint removers are caustic and solvent.
Paint Stripper Type 1 Caustics
Caustic paint removers, typically sodium hydroxide (also known as lye or caustic soda), work by breaking down the chemical bonds of the paint, usually by hydrolysis of the chain bonds of the polymers forming the paint. Caustic removers must be neutralized or the new finish will fail prematurely. In addition, several side effects and health risks must be taken into account in using caustic paint removers. Such caustic aqueous solutions are typically used by antique dealers who aim to restore old furniture by stripping off worn varnishes, for example.
Paint Stripper Type 2 Solvents
The principal active ingredient in historically common solvent paint strippers is dichloromethane, also called methylene chloride, which has serious health risks including death, is likely a carcinogen, and other risks.
Solvent strippers may also have formulations with orange oil (or other terpene solvents), N-methylpyrrolidone, esters such as dibasic esters (often dimethyl esters of shorter dicarboxylic acids, sometimes aminated, for example, adipic acid or glutamic acid), aromatic hydrocarbons, dimethylformamide, and other solvents are known as well. The formula differs according to the type of paint and the character of the underlying surface. Nitromethane is another commonly used solvent. Dimethyl sulfoxide is a less toxic alternative solvent used in some formulations.
The principle of paint strippers is penetration of the paint film by the molecules of the active ingredient, causing its swelling; this volume increase causes internal strains, which, together with the weakening of the layer’s adhesion to the underlying surface, leads to separation of the layer of the paint from the substrate.