ARCHITECTURAL SPECIFICATIONS FOR PAINTING, STAINING, ETC.
Architectural specifications for the painting, enameling, staining, and finishing of woods for first-class and medium grades of work, prepared by Mr. John Dewar at the request of the Master House Painters and Decorators of Pennsylvania, were endorsed by that Association, January 15, 1913. The essential portions of these specifications are quoted as follows: Painting New Exterior Woodwork Medium—All knots, rosin, and sap portions shall be properly shellaced. Paint one coat white priming brushed well into the wood, after which all nail-holes, open joints, and other imperfections shall be closed solid with putty containing 20 per cent white lead; then apply two coats of paint, colors to be selected. Each coat must be thoroughly dry before the application of another. Paint the back of all window and door frames one coat before setting, sash runners of window frames to receive two coats of oil, stained if required, the last coat to be applied at completion. No paint to be applied during wet or foggy weather. (See Note 1, below.) First-Class Woodwork should be painted as above specified, using one additional coat.
NOTE 1—All authorities agree that pure raw linseed oil and pure spirits of turpentine are the best vehicles for exterior paints. The vehicle of first or priming coat on new wood, also second coat, should consist of 80 per cent pure raw linseed oil and 20 per cent pure spirits of turpentine, the final coat 90 per cent pure raw linseed oil and 10 per cent pure spirits of turpentine, all to contain necessary driers. When four coats are used, the first, second, and third coats should be composed of 80 per cent oil and 20 per cent turpentine, the fourth coat 90 per cent oil and 10 per cent turpentine.
There exists some diversity of opinion as to the best paint pigment or pigments in combination. How necessary it should be that the construction of a paint film be as near perfect as possible. The necessity of this should be apparent to us all, especially when we are confronted with the fact that "the average paint coating is only three one-thousands of an inch thick, and yet this thin coating is required to withstand expansion and contraction of the underlying surface, abrasion or wear from storms of dust and sand, or rain, sleet, hail, and absorbing, drawing, and expanding influences of the summer's sun, and contraction from the cold of winter. It must have both hardness, to to a rea
sonable extent this surface wear, and yet enough elasticity to meet internal strain and to conform to changes in the underlying surface; and it must penetrate and cling to the surface upon which it is applied. It must also retard and prevent from access to the underlying surface both the moisture and atmospheric gases which cause decay ;" and, if possessing the virtues of a good paint, it must in the course of time, when repainting becomes necessary, present a suitable foundation for the new paint coatings.
It is generally accepted that a white or tinted base paint containing about 75 per cent white lead and 25 per cent zinc oxide is of a high standard. When used near or at the sea shore, also in the Southern States, it can be improved by a change to the following: 60 per cent white lead and 40 per cent zinc oxide. The purpose in combining these two best paint pigments are, that the one makes strong the weak points of the other, giving us an ideal paint coating. The zinc makes the film stronger and harder, also practically non-absorbent by reason of these qualities, and, with its fineness of texture, fills up the voids caused by the coarser pigment. After a most thorough and practical personal investigation as to results, I recommended the above combination, having used them in my practice for years. I have the manufacturer combine and grind the two pigments together, thereby getting a thorough amalgamation.
When the result required is a white or color-tinted paint, it is advisable to use the same percentage of different basic pigments and coloring matter in all of the coats, on account of obtaining a uniform expansion and contraction, solidity of color, etc.