Creosote mixed with coal-tar creosote, or fortified with pentachlorophenol. Water-gas-tar creosote is also derived from petroleum oil or shale oil, but by a different process; its distilled during the production of water gas. The tar is a by-product resulting from enrichment of water gas with gases produced by thermal decomposition of petroleum. Of the creosotes derived from oil, it is practically the only one used for wood preservation. It has the same degree of solubility as coal-tar creosote and is easy to impregnate into wood. Like standard oil-tar creosote, it has a low amount of tar acids and tar bases, and
Tar paper the oil crisis, felt weighed about 15 pounds per square (one square = 100 square feet) and hence the asphalt-impregnated felt was called "15#" and "15-pound felt". Modern, inorganic mats no longer weigh 0.73 kg/m2, and to reflect this fact the new felts are called "#15". In fact, #15 mats can weigh from 7.5 to 12.5 pounds/sq depending on the manufacturer and the standard to which felt is made (i.e., CGSB, ASTM D227 Standard Specification for Coal-tar saturated Organic Felt Used in Roofing and Waterproofing, ASTM D4990, Standard Specification for Coal Tar Glass Felt Used in Roofing and Waterproofing, or