XI. A, 4 Argiielles: Galvanized-iron Roofing 187 



those most commonly used in the Philippines. A few paint- 

 exposure tests were made, as follows: 



A rusted galvanized sheet which had been washed with dilute 

 hydrochloric acid to remove loosely adhering rusts and then 

 washed with water and dried was coated with the folloAving 

 paints : 



Primer : Parts. 



Sublimed blue lead 63 



Linseed oil 32 



Pure turpentine 5 



Second coating: 



Bright red oxide of iron 85 



Red lead 10 



Zinc chromate 5 



This paint has been exposed for three years and still renders 

 good protection to the iron sheet. The same paint was applied 

 on a new galvanized sheet, but it peeled off in less than a year. 



A graphite paint was applied on a new galvanized sheet. 

 After two years of weather exposure it shows slight peeling off 

 in several parts. 



Paint adheres better when it is applied after the surface of 

 the galvanized sheets has undergone considerable oxidation, 

 that is, after a year under weather exposure or when rusts 

 begin to appear. When so applied, it undoubtedly increases 

 the durability of the roofing. The use of paint for modern 

 galvanized roofing is a necessity in the Philippines and will 

 continue to be of immediate consideration to the consumer unless 

 manufacturers put more spelter on their future output. 



DISCUSSION OF RESULTS 



It is apparent from the foregoing experimental results that 

 the better service given by the old galvanized iron as com- 

 pared with the modern product imported to the Philippines is 

 accounted for by the greater amount of coating on the former. 

 This conclusion is in accord with observations made by others 

 elsewhere. For example, Van Gundy ^^ noted that galvanized 

 plate which had seen service of twenty or twenty-five years 

 in Panama was better than plate which had been in service less 

 than two years. Referring to the old galvanized sheet he said : 



Yet, even after this ser\rice, I found that it had three times as much 

 zinc on it as the American manufacturers put on their plate, even the best 

 in the market. 



"Proc. Am. Soc. Test. Mater. (1909), 9, 41. 



