Page:Popular Science Monthly Volume 91.djvu/788

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��bonate of lead, 4 gal. genuine kettle boiled linseed oil, or 9 gal. pure raw linseed oil, with $}4 pt. of Japan dryer and 1 gal. of turpentine. The second coat consists of 100 lb. carbonate of lead, 4 gal. pure linseed oil (% boiled and % raw) or 4 gal. pure raw linseed oil and 1 pt. of turpentine dryer. The finishing coat is prepared from 100 lb. carbonate of lead, ^A gal- pure linseed oil (}4 boiled and % raw, or 3^ gal. pure raw linseed oil and 1 pt. turpen- tine Japan dryer) and I pt. of pure gum turpentine. All these ingredients should be the purest and best of their kind. Inferior materials are likely to give un- satisfactory results. Zinc white is too hard for concrete painting.

Red lead is a very good pigment for the first coat on cement. It is more impervious to water than white lead, is elastic, and dries well. But if light color is to be placed on it there is likelihood of the red staining the light coat, unless a heavy second coat is applied.

As certain pigments are affected by an alkali, only those immune to lime should be used in painting over cement. For buff use yellow ochre; for a light yellow use zinc yellow (zinc chromate); for red use red ochre or bright iron oxide ; for blue use ultramarine blue, preferably the sulphate ultramarine; for green use ultramarine green or oxide of chromium green; for white use zinc sulphite (lithopone), zinc white not being desirable on account of its hardness or lack of elasticity; for black use mineral black, black oxide of manganese, black oxide of iron; for gray use graphite and lithopone, or lithopone and mineral black. All earth pigments are safe with lime; Venetian red gives a pleasing color.

In painting on cement it is customary to use plenty of turpentine, rather than much oil. Also very little dryer should be used. By using boiled oil we escape the use of dryers entirely. Some painters use all turpentine for the thinning of the first coat, or nearly all, with little oil, though the oil is increased with each successive coat of paint. If the finish is to be dead or with- out luster the first coat is thinned with turpentine only, making the paint very thin, adding a little varnish as a binder. The next coat is similar. The third coat should be thinned with 3 parts boiled linseed oil and 1 part turpentine. The finishing coat is thinned out with turpen- tine, with a little varnish as a binder.

A number of special coatings for cement

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��are on the market, guaranteed by the makers to be proof against alkali. The waterproofing qualities of some of these preparations are overdrawn. To test such a liquid, take a fairly porous brick and apply to it as many coats as would be placed on the cemented surface; but two coats are better than one in any case, particularly where a very light color is to be used. Let the brick dry, then weigh it, make a note of the weight, then place the brick ' in a vessel with water just sufficient to cover the brick; after about one-half day remove brick, wipe off moisture, again weigh it, and compare with weight previously noted. The differ- ence in weights will show amount of water taken in through the paint.

Try different paints. The one that shows the greatest water-resisting power is the one to use. Where concrete silos are used, a waterproof paint is useful. On the inside it prevents the liquid from the ensilage from soaking into the wall, and as silage is acid this would injure the coating of cement. Tar is often used as a coating for this purpose, and it does very well.

Besides the colored coatings there are a number of so-called colorless waterproof cement coatings on the market. These are intended for use where the color of the cement is to be preserved. They are also largely used as a preservative for limestone, sandstone, etc. The oldest used preserva- tive for this purpose is paraffin, applied hot with a brush. Concerning the useful- ness of the colorless liquid coatings, some of them are of some value in retarding moisture, but all are found lacking in the following respects: They emphasize any defects in, or difference in, color of concrete construction; they impart to concrete a s °ggy» water-soaked appearance; they do not render it impervious to water for any great length of time; they do not decorate.

The following process for painting ce- ment surfaces is favored by many expert painters. Slake a half-bushel of fresh stone lime in a barrel, and add in all 25 gal. of water; when cold, after slaking, add 6 gal. of pure cider vinegar and 5 lb. of the best dry Venetian red. Mix well and pass through a 'fine strainer. Thin to the con- sistency of thin cream. Apply a coat of this to the cement, and after a day or so, or when dry, apply a coat of red lead mixed in raw linseed oil. When the red lead paint has become* dry any other colored paint may be applied, but care should

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