January, 19 lo 



AMERICAN HOMES AND GARDENS 



39 



Painting Concrete Houses 



By George E. Walsh 



I'NE of the advantages claimed for concrete 

 houses is that the cost of repairs are slight 

 from year to year, and that the exterior 

 surface does not require frequent painting 

 to protect it from the elements. For this 

 reason concrete residences by the seashore, 

 where the strong salty air quickly destroys 

 ordinary paint and rots the wood, have grown into popular 

 favor the last few years. Apparently the harsh sea-air 

 has no visible disintegrating effects upon the concrete sur- 

 faces. This strong feature of concrete structures carries 

 with it one disadvantage which has caused an endless amount 

 of discussion and experiment. Concrete surfaces, while 

 proof against weather conditions, present such a monotous 

 color that from an artistic point of view many object to 

 using the material for their homes. 



But for all that we have the dull blue-gray of ordinary 

 Portland cement which offers little variety in effects when 

 compared with the red and buff of terra-cotta or the clear 

 white and warm gray of marble and granite. To secure 

 the highest artistic results in concrete residences, therefore, 

 builders and architects contend that we must have variety 

 in color. 



There are two methods adopted to secure colors in con- 

 crete houses. One is to mix coloring ingredients with the 

 cement which will present lasting qualities, and the other is 

 to paint the exterior surfaces with some paint which will 

 give somewhat similar results. The mixing of different 

 colored sands with the cement to get color-schemes, and the 

 adding of certain oxides to the mixture to intensify certain 

 shades are still in the experimental stage. 



The difficulties in the way of applying colors to the ex- 

 terior after the concrete house is finished are somewhat 

 similar to those which apply to exterior painting of frame 

 houses. The weather affects them and necessitates repaint- 

 ing at intervals. The use of lead and oil paints is not of 

 lasting quality. The alkali of the cement has an affinity 

 for linseed oil, and in time the oil oxidizes and causes the 

 paint to peel off or dust. 



Experimenters have realized for years that the ideal 

 paint for concrete houses must be something more than 

 a thin film. It must be a composition that will penetrate 

 the surface and fill pores so that firm adherence can be 

 obtained. A paint composed of color-pigments with ground 

 cement as the base gives good results. The light chemical 

 oils used are intended to dry out after performing their 

 function of bonding the cement base to the concrete sur- 

 face. The cement base thus becomes a part of the wall 

 and holds its color indefinitely. 



When nature in the form of wind, rain and sunshine 

 has neutralized the alkalies of the cement, it is much easier 

 to paint the exterior structure and secure more durable 

 results. Consequently, it is unwise to figure upon having 

 a stucco or concrete house painted when finished. If this 

 is intended, the highest results cannot be expected. Old 

 concrete houses that have stood exposed to the weather for 

 a year or two are in much better condition for the painting. 

 The new house painted can not undergo the same aging 

 process. The film of paint is waterproof, and hence checks 

 the process of neutralization of the alkalies in the cement. 



If the house has had an opportunity to dry thoroughly 

 the question of painting the exterior surface to get another 

 color can be considered with hope of success. Nearly all 



of the different methods of applying paint to cement sur- 

 faces have been tried on new houses, and the experiments 

 were conducted with the fresh concrete or stucco in view. 

 Therefore, all of these apply with greater force to the houses 

 which have been allowed to stand a year or two and dry 

 out. 



One of the earliest processes was to treat the cement 

 surface first with a wash to clean the surface and neutralize 

 the alkali. Diluted muriatic acid or hydrochloric acid of 

 seven to eight per cent, mixed with clean water composed 

 this wash. After treating the entire surface all dirt, grease 

 and other substances were removed, and the neutralizing 

 of the alkali of the cement was hastened thereby. But, 

 unfortunately, if the cement contains much lime, which is 

 \ery commonly the case, the muriatic acid would tend to 

 neutralize the lime and convert it into calcium chloride. 

 This would prove most injurious to the cement surface. 

 It would crumble and pit the surface, and when paint 

 is applied to such a surface it would have a very uncertain 

 foundation. Any application of such a wash to the ce- 

 ment, therefore, means disintegration of both the surface 

 and the ordinary paints. In the use of muriatic acid as a 

 wash, and also sulphuric acid, which some have employed, 

 an excess of acid is supposed to be washed off before the 

 paint is used, but in spite of this the acid generally does 

 injury to the surface. 



There is a method called the zinc sulphate, which gives 

 much better results than either of the former applications 

 and its cost is less. When the cement has dried properly 

 an application is made of a zinc sulphate and water of 

 equal parts by weight. When thoroughly mixed this solu- 

 tion is applied over the whole cement surface with a stiff 

 brush. A fine coat is thus formed, which at the end of two 

 or three days dries hard and firm. The zinc sulphate 

 changes the caustic lime of the cement into calcium sulphate 

 or gypsum, and zinc oxide is deposited in the pores of the 

 cement. 



Zinc sulphate is one of the most important of the white 

 paint pigments, and when paint is subsequently applied, this 

 becomes incorporated with it and gives lasting and durable 

 qualities. The zinc sulphate has no known injurious effect 

 upon concrete or cement surfaces, and consequently there is 

 no disintegrating chemical change set up. This method of 

 treating cement surfaces to prepare them for painting has 

 been used successfully on a great number of private and 

 public buildings. In preparing cement surfaces for painting 

 consideration must be observed as to the effect the first 

 application may have both upon the cement and the paint. 

 The strong acids that destroy the cement can not be recom- 

 mended anywhere. 



There are several other methods of preparing cement 

 and concrete for painting, so that durable color-effects can be 

 obtained, and some of these have given excellent results. 

 One of these is to coat the surface with a solution of ten 

 pounds of carbonate of ammonia to 45 gallons of water. 

 The solution is applied with a brush once and left to dry. 

 Insoluble calcium carbonate is formed on the cement sur- 

 face, and a large amount of ammonia is liberated. This 

 leaves a perfect surface for painting. Where mortar con- 

 taining lime is used in building a stucco house, it is better 

 to use two weak solutions of this mixture rather than one 

 strong solution. The surface of cement is not injured 

 by this wash, 



