216 PAINT TECHNOLOGY AND TESTS 



a material having an exceptionally high acid value and thus 

 lending itself successfully to the neutralization of free lime. 

 It has been claimed, however, by certain practical painters that 

 the lime-rosin compounds formed when such paints are applied 

 to the exterior of buildings, are of a brittle nature and subject 

 to early failure. If this is true, it would seem advisable to use 

 in a concrete paint an oil of a relatively unsaponifiable nature, 

 which would withstand successfully the action of the lime, and, 

 at the same time, prevent disruption of the coating and failure 

 of the color used in the paint. 



Outline of Tests. The tests referred to as carried out by the 

 writer were made on a brick wall forty feet long, surface-coated 

 with a four-inch coating of Portland cement mortar made of one 

 part of Portland cement and three parts of sharp, clean sand. 

 After the cement had hardened for three days, the solutions under 

 test were applied. 



In many of the tests outlined above, one-coat, as well as two- 

 coat work, was used on different sections of the test surfaces. 

 It was shown that the two-coat work gave far better results than 

 with the one-coat work, and the writer would recommend for 

 the painting of concrete at least two-coat work. Whenever 

 paints containing Prussian blue or chrome green are applied to 

 concrete surfaces, immediate whitening in the case of the blue, 

 and yellowing in the case of the green, will take place, if any 

 degree of action has been exerted by the lime within the con- 

 crete. For this reason, green is an especially delicate color to 

 test and should be utilized for this purpose. 



The materials used, and the results shown at an inspect : on 

 made after two years' exposure, are given herewith. 



Test No. i. Concrete primed with a 25% solution of zinc 

 sulphate crystals dissolved in water. A wide brush was used 

 for the application, and the spreading rate was approximately 

 200 square feet per gallon. Second and third coated on the 

 second day with No. 119 blue paint of the following composition: 



No. 119 BLUE PAINT 



Sublimed white lead 50% 



Zinc oxide 35% 



Silica and barytes 12% 



Prussian blue 3% 



Ground in linseed oil, turpentine and drier. 



