This line of paint making is coming to the fore rapidly and there are, even now, many brands on the market that are offered for the purpose of coating such surfaces to keep them from dusting or withering and to make them pleasing to the eye as well by color schemes when it comes to walls, interior and exterior as well. A most important feature, however, is the coating of cement floors, concrete reservoirs, silos, cisterns, etc. Here is the most difficult problem for the paint maker, and very few of the brands offered for the purpose so far have given satisfactory results. Up to within a few years ago various preparatory treatments for concrete and cement surfaces have been suggested to be applied in advance of painting, but while at least one of these gave satisfactory results in holding back alkalinic action of cement, even this was finally frowned upon by consumers as being a waste of time and labor, and the demand was for paint coatings of a nature that made the application of chemical solutions unnecessary. Carbonate of ammonia in solution was one method suggested for treating new cement walls, while a saturated solution of zinc sulphate as a wash in several applications was another, and a third was a solution of eight parts oil of vitriol in 92 parts water for roughening the surface and converting the lime in the cement into the harmless sulphate of calcium, to be followed with any good priming paint as used on interior or exterior work generally finished in the usual manner. The sulphuric acid treatment has no found favor, because it affects the surface of the cement too strongly, and as pointed out above, the other treatments were found too cumbersome. It would be a waste of time to describe the compositions of the patented concrete coatings which appear to cover almost any possible vehicle that would seem to go far towards holding back the action of fairly fresh cement. Some of the other brands that have been selling fairly well show a composition of equal parts zinc oxide and either calcium carbonate in the form of marble dust, or calcium sulphate in the form of gypsum, or lithopone white and zinc oxide with magnesium silicate for pigment with a vehicle of linseed oil, gloss oil, pale drier and heavy naphtha. These, while comparatively low for cost, are not well adapted for waterproofing walls or for use on floors, unless finished eventually with other paints that give the finish desired.
It is an established fact that linoleic acid is a good coating for holding back lime in cement mortar, but in order to make it available in a concrete or cement coating, it is best used in connection with other vehicles. The following formula has been tried with very satisfactory results on various cement plasters, both inside and exposed to the weather: - Ten pounds of builders' lime are slaked with three gallons of water and covered up. After 24 hours the liquid is poured off, filtered through cloth, and set aside. Grind in a suitable mill 60 pounds Green Seal lithopone with 10 pounds raw linseed oil and 12 pounds refined paraffne oil (paint oil). Return this to a change can mixer and add first four pounds of the above lime solution, and then eight pounds linoleic acid and six pounds of pale tungate drier. This produces 100 pounds of a stout paint, weighing 15 pounds per gallon, but is most too stout for easy working on porous surface and should be reduced with one gallon heavy petroleum naphtha, producing seven and two-thirds gallons of paint, weighing 14 pounds per gallon. The lithopone can be replaced by zinc oxide, but in that case it is advisable to use a portion of finest floated barytes, say two-thirds zinc and one-third barytes. For tinting this paint only lime proof colors should be used, and when the proportion of color is small, the colors are best ready ground in linseed oil, otherwise where deep colors are wanted the dry colors are best ground together with the white pigment, increasing the vehicle portion accordingly. Limeproof colors comprise all blacks, ultramarine blue, oxide of chromium green, green earth, yellow and red ochers, red oxides, siennas and umbers, raw and burnt, also zinc chromate. Paint made by the above formula will seal the concrete or cement surface with one application, but, of course, show a dull finish, nor will it dry with high gloss on second coat, but will make an effective priming coat for walls and floors as well.