Turpentine does not burn the paint as many believe. Turpentine evaporates the slowest of any of the volatile paint solvents. It is used to give ease in working, form depth of penetration and assist in drying. Use turpentine liberally in priming or middle coats. When used in undei'-coatings, turpentine reduces the gravity of the oil and assists in opening the pores of the wood, thus allowing of greater depth of penetration. If used in middle coats or for recoating old surfaces, it assists in penetrating the previous coating and materially helps to cut the oil which is the gloss of the paint, leaving a better tooth for the binding of the finishing coat.
Never substitute gasoline or benzine for turpentine, they are not substitutes. Gasoline is not a paint solvent, it is the lightest of the petroleum products and worthless as a substitute for the use to which turpentine is put. Benzine and naphtha, while better paint solvents than gasoline, are light petroleum products of high specific gravity, reducing rapidly and evaporating quickly, they do not penetrate but evaporate on the surface, making the paint work hard, retarding the brushing out of paint and preventing working the pigment into the pores of the wood, leaving too much pigment and a dangerous undercoat without sufficient penetration or binder.
Study the surface to be painted and use turpentine in the reduction according to the condition of the surface. If new work, constructed of hard, close-grained lumber, more turpentine must be used than if constructed of soft, open-grained lumber of quick absorption. The liberal use of turpentine in priming improperly seasoned lumber or lumber which contains moisture will assist in producing better penetration.
In repainting an old surface, the first coat must be reduced with turpentine according to the porosity of the surface. If a hard, flinty surface, much more turpentine must be used than if porous or weather-beaten. The mixture should range from flat, half flat to semi-gloss. Never apply a heavy coating of full oil reduction.
Paint which has become fatty and gummy can be partially remedied by the addition of a small amount of turpentine. When painting in hot, humid weather, a small amount of turpentine added to the finishing coat will aid in hardening the paint.