Asphalt and coal tar pitch are different grades of petroleum derivatives. These products are combined with layers of felt then topped with small gravel (to protect the roofing from ultraviolet rays) to constitute a roof. After a certain amount of years the oils dry out and cause the roofing material to crack. Coatings can be of petroleum based products (restaurants) or non-petroleum based products. The petroleum based products have been in use longer and likely work better. Asphalt roofing cement and fiberglass mesh can also be used to repair small problems. Pitch roofs (which smell like kerosene) usually last the longest. Pitch has a lower melting point and can sometimes melt into cuts or cracks in high summer heat, making pitch roofs the longest lasting of any we have come across. Check for ponding (see special ponding section on other page).