Color of Concrete Blocks

COLOR OF CONCRETE BLOCKS Outside of all considerations of form and ef fect, the matter of color is not the least impor tant of the properties of the concrete block. It is upon this more than anything else that the marketing of the block depends. It is, there fore, important to secure uniformity of color, and an effect that will be pleasing to the eye. This requires constant study to attain in its per fection, and is one of the greatest problems of the business. For colored blocks, dark-colored cements may be used to the best advantage, but their color should be uniform. For lighter blocks, cement of lighter color must be used. Cement gets lighter as it is ground finer, and only finely ground cement should be employed for this work. Cements entirely free of manga nese and iron would be white; and the color grows dark as the percentage of iron and man ganese increases. Most cements, however, have more iron than manganese, and the color, there fore, is due to the iron.

Sulphate of lime, which is always added to cement to regulate the set, is responsible for the white efflorescence of blocks. The salt is sol uble, and is carried to the surface of the blocks during the curing process.

In coloring artificial stone to a gray, the use of one pound of Germantown lampblack mixed with cement dry, and one pound of salt pre viously dissolved to every ten gallons of water, greatly assists to waterproof the product, but does not make an absolutely waterproof stone, although increasing the lampblack makes the stone less absorbent and affects the durability.

Black stone

is produced by adding peroxide of manganese to the cement in the proportion of twelve to fifty pounds per barrel of cement.

The amount is governed by the color of the sand and cement, or by adding from two to four pounds of excelsior carbon black to each barrel of cement. The manganese in a measure pre vents the absorption of water, but the excelsior carbon does not; the first reduces the strength, and the other has little or no effect upon the dur ability or strength of the product.

Blue.

The use of any waterproofing in making black stone will discolor the surface. In producing waterproof blue stone, the best re sults are obtained by using five pounds of ultra marine blue, one pound of pulverized alum, and one pound of soda mixed dry with the cement. This produces a very sound product, less sub ject to moisture than perhaps any natural product.

Red

artificial stone, made either of oxide of iron or Pompeian red, will not mix well with waterproofing compounds, and it is the opinion that reduction of the absorbing qualities can be done only after the colored product has hard ened.

Brown or Buff.

In making brown or buff stone, ocher, which in a measure prevents mois ture, is employed; but ocher is detrimental to strength.

Table II, based on experiments made by L. C. Sabin, an authority on the subject, shows the color results obtained from a dry mortar, the mortar containing two parts sand and one of cement.

Mix Coloring with Cement.

In the produc tion of colored blocks, the coloring matter should be mixed with the cement so that in effect it will be colored cement that will be mixed with the sand. This method assures a thorough coloring of the block, and a uniform shade throughout.