Topic summary
Felt paper
Extracted from the Wikipedia article Bituminous waterproofing.
Weights and grades
Felt paper is available in several grades, the most common being Type 1—commonly called 15-pound (15#) or No. 15 (#15)—and Type 2—commonly called 30-pound (30#) or No. 30 (#30). The weight designations originated with organic base felt weighing 15 or 30 pounds per 100 sq. ft. (0.73 or 1.46 kg per m). However, modern base felts are made of lighter-weight fibre, so the weight designations, though common colloquially, are no longer literally accurate. A heavier class of materials with a similar construction but designed for civil engineering, environmental protection, and mining applications are known as Bituminous Geomembranes (BGMs). BGMs are distinguished in part by larger roll widths which can exceed 5 m and substantial thickness of up to 6.0 mm.