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The composition of these paints is quite different from that of oil paints, and their use is generally confined to small surfaces except when applied with a spray gun. Cellulose paints dry by the evaporation of the solvents, and this makes it impracticable to coat large areas by brushing methods as the solvents evaporate so quickly that the paint begins to dry before it is properly brushed out and the brush drags, leaving an uneven coating. The solvents used in these paints also dissolve old coatings of oil paint so that discrimination is necessary when using them to repaint surfaces previously finished in oil paint or varnish.
As a general rule, the older, (i.e., more oxidized), the paint the less likely is the cellulose paint to disrupt it, but before commencing any work a small area should be coated as a test.
To prevent or minimize the solvent action of cellulose paints, special undercoats are sold; these form an isolating coat between the old paint and the cellulose film. Undercoats are also necessary when starting from bare wood and other absorbent surfaces as they overcome the suction, fill the grain, and provide a good groundwork for the cellulose which permits it to dry with a good full glossy film.