Tar and gravel roof cover is used primarily on roofs with low slopes ranging from a little better then flat to somewhere around a 3-in-12 slope - (that's roofing talk for three inches of vertical rise for every twelve inches or horizontal run).

This type of roof is composed of alternating layers of roofing felt and hot tar and is often referred to as a hot mopped or built-up roof. It sounds as if you have a variation of this. That is that you have a built-up or hot mopped roof which does not contain gravel. A tar and gravel roof without the gravel so to speak.

With conventional tar and gravel roofing the tar is covered with a thin layer of gravel to protect the tar from the harmful ultra violet rays of the sun. Contrary to popular belief it is not water and rain that are responsible for the majority of the damage to roofing products, it's the constant exposure to the sun which, in the case of your type of roof, rob the tar of solvents which cause it to become brittle, crack, or blister.

Another popular way to protect a built-up roof from the sun is with the application of an aluminum coating in lieu of the gravel. However, according to roofing experts this method doesn't offer the roof the level of protection from the sun that gravel does. Unlike the gravel, which will not deteriorate unless eroded by excessive wind and rain, the aluminum coating will only last five to seven years before an additional application is required where the conventional tar and gravel roof should last somewhere in the neighborhood of fifteen years. We suggest that you go with the gravel.