MISCELLANEOUS PAINTS 339 



To obtain the best results in painting metal structures therefore, 

 proceed as follows: (i) prepare the surface of the metal by carefully 

 removing all dirt, grease, mill scale, rust, etc., and give it a priming 

 coat of pure linseed oil or a good paint red lead seems to be the most 

 used for this purpose; (2) after the metal is in place carefully remove 

 all dirt, grease, etc., and apply the finishing coats preferably not less 

 than two coats giving ample time for each coat to dry before applying 

 the next. Painting should not be done in rainy weather, or when the 

 metal is damp, nor in cold weather unless special precautions are taken 

 to warm the paint. The best results will usually be obtained if the 

 materials are purchased in bulk from a responsible dealer and the paint 

 ground as wanted. Good results are obtained with many of the patent 

 or ready mixed paints, but it is not possible in this place to go into a 

 discussion of their respective merits. 



ASPHALT PAINT. Many prepared paints are sold under the 

 name of asphalt that are mixtures of coal tar, or mineral asphalt alone, 

 or combined with a metallic base, or oils. The exact compositions of the 

 patent asphalt paints are hard to determine. Black bridge paint made 

 by Edward Smith & Co., New York City, contains asphaltum, linseed 

 oil, turpentine and Kauri gum. The paint has a varnish-like finish and 

 makes a very satisfactory paint. The black shades of asphalt paint 

 are the only ones that should be used. 



COAL-TAR PAINT. Coal-tar used for painting iron work 

 should be purified from all constituents of an acid nature ; for this rea- 

 son it is preferable to employ coal-tar pitch and convert it into paint 

 by solution in benzine or petroleum. Tar paint should preferably be 

 applied while hot. Oil paint will not stick to tar, and when repainting 

 a surface that has been painted with tar it is necessary to scrape the 

 surface if a good job is desired. Tar paint does not become hard and 

 will run in hot weather ; it is therefore not a desirable paint to use for 

 many purposes. 



CEMENT AND CEMENT PAINT. Experiments have shown 

 that a thin coating of Portland cement is effective in preventing rust ; 

 that a concrete to be effective in preventing rust must be dense and 

 made very wet. The steel must be clean when imbedded in the concrete. 

 There is quite a difference of opinion as to whether the metal should be 

 painted before being imbedded or not. It is probably best to paint the 



