TECHNIQUES OF MIXING AND THINNING

TM 43-0139 3-8. TECHNIQUES OF MIXING AND THINNING a. Method. The best, quickest, and easiest method of painting is by spraying. Paint rollers are used on large surfaces when spraying is impractical. Paints are brushed on when other methods are impractical or special equipment is not available. In general, the use of brushes is confined to touchup jobs. b. Readiness. In most cases, paints issued ready mixed, hence color blending is not required. CARC paints MIL-C- 56168 and MIL-C-22750, however, are issued in a two-component form and require accurate mixing techniques. c. Preservation. (1) String. Stir paints well before use. If the vehicle (liquid portion) has separated from the pigment, pour off most of the liquid portion into a clean container. Stir the thick settled portion (pigment) in the bottom until all chunks are softened and dissolved. Restore the poured off portion a little at a time, stirring constantly with a lifting and beating motion. "Box" the paint thoroughly by pouring it from one container to another several times, stirring the paint for a few minutes between each transfer. NOTE Do not "box" lacquer, as this will cause a loss of the liquid portion by evaporation. (2) Straining. When paint stands over a period of time, a skin may form over the surface and the pigment may form into chunks to the extent that stirring will not mix all of the ingredients properly. In such cases, strain the paint through a strainer into a clean container, discarding the residue left ion the strainer. Do not strain CARC coatings, however. CARC coatings which cannot be properly mixed will be resealed and disposed of as hazardous wastes. (3) Thinning. (a) When it is necessary to thin paint, use a small amount of the prescribe thinner. Because of its volatility, thinner will evaporate from the paint film, leaving practically the same ratio of vehicle to pigment per square foot of surface as the paint would have provided before thinning. The warmer and drier the weather, the less thinner is needed because heat tends to thin the vehicle. More thinner is required in cold weather to hasten the drying and hardening of the film. Thinner should be used with care, as the less used, the more durable the applied coat will be. (b) Polyurethane coatings may be thinned up to 20 percent by volume with thinner MIL-T-81772, Type I, or with the manufacturer's recommended thinner. Epoxy primers which are admixed (blended) four to one by volume, such as MIL-P-53022, may be thinned up to 20 percent by volume with epoxy thinner MIL-T-81772, Type II. Epoxy enamels and primer which are admixed one to one by volume, such as MIL-C-22750 and MIL-P-23377, usually have satisfactory spray viscosities, but may be thinned with small amounts of MIL-T-81772, Type II, if necessary. Water is used to thin MIL-P-53030. (c) Paints which contain a slow-drying vehicle may require additional thinner. (d) Varnish should not be thinned except when used as a primer coat; it should then be thinned with a small amount of its recommended thinner. NOTE Do not shake varnish. This may entrap air which will be difficult to eliminate from the film. (e) To thin synthetic enamels, use synthetic enamel thinner, TT-T-306. Change 3 3-6