Paint Technology and Tests Part 22

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 concrete. 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 inspection made after two years' exposure, are given herewith.

=Test No. 1.= 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.

This panel, after three years' exposure, is in good condition. Slight checking observed.

=Test No. 2.= Concrete primed with a 20% solution of (alum) (aluminum sulphate). Second and third coated with No. 119 blue.

In similar condition to Test No. 1.

=Test No. 3.= Concrete primed with zinc sulphate followed by two coats of para red.

PARA RED FORMULA

Blanc fixe 60% Whiting 25% Zinc oxide 3% Paranitraniline lake 12%

Ground in linseed oil, turpentine and drier.

Panel in fair condition with exception of slight crazing. Characteristic dullness of color after exposure shown. Bright red color restored upon washing.

=Test No. 4.= Concrete primed with an 8% solution of stearic acid and rosin dissolved in benzine. Second and third coated with No. 119 blue.

This panel is not in as good condition as Tests Nos. 1 and 2, and would indicate the inferiority of the priming liquid used. Color failing in spots and checking observed.

=Test No. 5.= Concrete primed with mixture used in Test No. 4, and then given two coats of para red.

Test is in about the same condition as No. 4.

=Test No. 6.= Concrete primed with a 10% mixture of acid calcium phosphate, followed with two coats of No. 119 blue.

The acid phosphate solution evidently had a neutralizing effect upon the lime in the concrete, as the paint is in fair condition.

=Test No. 7.= Concrete primed with one coat of a soap emulsion of the following composition, then painted with two coats of No. 119 blue.

Water 85% Linseed oil 12% Alkali 3%

Very poor results obtained. Destruction of color and peeling resulted.

=Test No. 8.= Concrete primed with one coat of white paint of the following composition:

PRIMER

Zinc oxide 25% Silica 35% Corroded white lead 20% Gypsum 15% Whiting, etc. 5%

Ground in a vehicle of linseed oil and containing 35% of volatile hydrocarbon spirits and drier.

This coat was followed by one of the following composition, tinted blue:

Zinc oxide 60% Gypsum 20% Silica 20%

Ground in linseed oil with 12% of turpentine and drier.

Fair results shown during first year, but a breakdown occurred during the second year, and cracking and scaling resulted.

=Test No. 9.= This test was a duplicate of No. 8 with the addition of 5% of zinc sulphate solution emulsified into the primer.

Slightly superior to Test No. 8.

=Test No. 10.= Primed with a white paste paint thinned with turpentine.

Second coated with same paint tinted blue.

FORMULA OF PASTE

Zinc oxide 40% Whiting 30% Silica 20% Alumina and gypsum 10%

Ground in 16% of linseed oil vehicle.

Scaling and peeling due to lack of binder and use of saponifiable oil resulted during the first six months' exposure. Entire destruction of coating at end of two years.

=Test No. 11.= Primed with a white mixture, and second coated with the same mixture tinted blue.

FORMULA OF MIXTURE

Whiting 30% Silica 30% Zinc oxide 40%

Stirred into a 5% solution of glue in water, until a fairly thick paste was obtained.

Much chalking was shown, and a bleaching of color. It is evident that this mixture would not serve to keep moisture out.

=Test No. 12 A.= Primed with a 5% solution of soluble nitrated cotton and paraffin dissolved in equal parts of amyl acetate and benzine.

Second coated with No. 119 blue.

Not very good results were obtained, chalking and slight scaling resulting.

=Test No. 12 B.= Primed with a heavy varnish containing Chinese wood oil and kauri gum. Second coated with No. 119 blue.

Fair results obtained.

=Tests Nos. 13, 14, 15, and 16.= Primed with a solution made by dissolving 10 parts of sodium oxalate in 100 parts of water. Second and third coated with linseed oil paints in red, brown, blue, and green.

Very good results shown at end of test.