Waterproof

Popular Science, huhtikuu 1942

By Maurice Wharton



Paints that are prepared for use simply by adding water, that anybody can apply over almost any type of surface, that dry in less than an hour, and withal are permanent and washable, sound like a home planner's dream. Nevertheless, they are very much a fact, widely used y interior decorators and deservedly popular.

These paints are available in white and pleasing pastel shades such as ivory, gray, tan, blue, orchid, and coral. Brillian "fresco" colors can be had for mixing in-between shades, painting on stencil designs, and creating special effects. Beautiful modern treatments such as broad gradated bands of a single color shaded from the pastel tint to its deepest tone, known technically as "let-downs," are possible by progressive mixing. One such effect is illustrated above.

A possibility not to be overlooked is the creation of stunning backgrounds for color photography. The amateur photographer, by using inexpensive wall-board panels and water paints, can make a variety of color screens and background sets.

These comparatively new water paints come in both powder and paste form. In general, they all possess the same properties of quick drying, clear colors, very flat finish, ease of application, and freedom from strong afterodor. Interiot water paints can be applied directly to plaster - even when it is still slightly damp - as well as over brick, wallboard, wood, metal, wall paper, and oil paint. Exterior finishes of this type may be used on brick, concrete, stucco, except magnesite), and other painted or unpainted surfaces. Because priming coats are rarely neede, and because water paints are applied with wide brushes, they afford a very economical means of finishing. However, they do not bond perfectly to glazed surfaces such as some types of tile and brick, nor should they be used for finishing rooms subject to steaming, such as bathrooms, kitchens, and laundries. Oil paints or enamels are preferable for such purposes, and worth the difference in cost.

The casein powder type of water paint is usually a mixture of dry casein, hydrated lime, and pigment. It should be allowed to stand for 20 or 30 minutes after mixing before it is applied. This type of paint is especially suitable for covering damp surfaces containing strong alkali, such as green concrete or fresh plaster.

More recently, water paints have been developed in paste form. these include casein, soybean protein, and resin paste paints. The casein paste paint contains pigments of great hiding power, such as lithopone and titanium dioxide. It is easily brushed on, dries quickly, and provides a very attractive flat pastel finish, which may be cleaned with a sponge and a mild soap solution.

Soybean paste paint, in which soybean protein serves the same purpose as casein, has an even cleaner odor. It is also easier to preserve and is claimed by some experts to stand up slightly better on damp walls. Some water paints combine casein and soybean protein, and the advantages of both.

Resin paste water paint, which is another variety, is prepared for use by adding half of gallon of water to a gallon of the paste. It consists of what are called "alkyd resins," emulsified into water, usually with a small amount of protein to stabilize the emulsion, and suitable pigment. The advantage of resin paints over casein and protein paints is that, when they dry, the resin is highly water resistant. Such paints willwithstand a surprising amount of washing and scrubbing, being comparable in this respect to flat oil paints. They are especially suitable for covering alkaline surfaces, such as green concrete or fresh plaster.

For outdoor use two coats give a sufficiently thick film to withstand weathering. A good outdoor resin paint, properly applied, will last several years and present an attractive finish during this time. These paints are "self-cleaning," in that they chalk off at a very slow rate, and rain washes off surface dirt along with the fine dust.

To mix resin paste paint, use only clean galvanized iron buckets. Add water only as fast as the paint can take it up, stirring thoroughly. In cold weather, mix outdoor water paints with warm water. If freezing temperatures prevail, use a half-and-half water and alcohol mixture.

Calcimine and whitewash must be thoroughly removed before modern water paints are applied. Glossy or greasy surfaces on which the paint "crawls" should be scoured with washing powder before painting. Where plaster flakes, chalks, or shells easily, brush off all loose material and apply a flat, pigmented, oil-type wall size. Casein size is also satisfactory, but blue, water sizes, sealing varnish, and shellac are not suitable for use under water paints. Surfaces that have been treated with alum or zinc sulphate, or with sizes containing these substances, must be washed with a strong washing-powder solution. Where effervescent mildew, acid, or excessive dirt and grease conditions exist, a trisodium-phosphate wash is advisable, followed by a water rinse. It is not necessary to wait for the surface to dry before staring to paint. In preparing old surfaces, fill all holes or cracks with patching plaster. Give patches a preliminary coat of the finishing paint.

Outside surfaces should be clean and free from dirt, dust, or grease. Remove old cold-water paints or whitewash. Clean off oil or grease with gasoline. Use a scraper or wire brush to remove any rust or loose, scaling materials. Hard rust spots and metals susceptible to rust should be primed with a rust-inhibitive paint. Point up holes and cracks with suitable patching material and coat these spots before painting all over.

No surface preparation is necessary when painting new concrete, stucco, limestone, and masonry surfaces. Do not neutralize lime before applying the paint. However, if an acid was has been applied, it will be necessary to neutralize this acid with an alkaline solution. Caution should be exercised when painting reclaimed brick, improperly kilned brick, or mortar joints made with unwashed sand. The paint will not form a proper bond with any powdering brick, cement, or limestone surface.

Deeply embedded, bleeding stains become visible after the first coat of paint and should be sealed before applying a second coat. Be sure that rood flashings, gutters, cornices, and the like are in good condition before starting the paint job.

A good, clean calcimine, Dutch calcimine, or large paintbriush with soft, flexible bristles is suitable for applying most water paints. Keep the brush well filled at all times.

If the paint becomes too thick during application, it may be thinned by the addition of small amount of water. One coat will be satisfactory in many instances, but on new surfaces and on surfaces where extra durability is desired, two coats are recommended.

Allow the first coat to dry at least dfour hours before applying the second one. In other cases, provided that there is sufficient ventilation to speed evaporation, pictures and furnishings may usually be replaced within an hour after painting.

Contrary to general belief, white and such light tints as buff and cream have the highest one-coat covering efficiency.

Immediately after use, all brushes should be cleaned in a soap solution. If brushes have been allowed to dry with the material on them, they can often be softened in benzine.

Do not attempt to wash water paints until they have been on the surface at least 30 days. After this you can brush or sponge the surface with a mild soap solution, washing the latter off with clean, lukewarm water immediately after it has been applied. Start washing at the floor and work up to the ceiling. Wall-paper cleaner gives excellent results and is especially recommended where the paint has been applied to a porous surface. Do not attempt to scrub casein and soybean protein paints.