What Is the Composition of a Grit Sand Roof Shingle?

Limestone

• Over time, stone that has been exposed to weathering will gradually form debris and sand particles. Sand particles are also formed by manually grinding stone into small particles. The sand, or grit, present on asphalt-based composition roll roofing and shingles is usually ground limestone. Limestone is a sedimentary rock with dense characteristics. Limestone's small pore size allows it to withstand water absorption. Limestone granules are used as a protective coat on shingle surfaces. The coating helps shed water from the roof's surface. This lack water absorption prevents warping and damage from freeze and thaw cycles.

Asphalt Shingles

• Shingles made of wood, stone, tile and metal do not feature a protective grit layer. Asphalt shingles, however, receive this protective coating. The protective layer is responsible for providing weather protection, but it also adds color to the roof shingle. This allows homeowners to choose from a range of colors. Asphalt shingles feature a fiber-based core that is layered with asphalt. The asphalt is treated, pressed and dried. The result is a relatively lightweight shingle that is capable of lasting between 15 to 30 years.

Composition Roll

• Composition roll roofing, or grit roofing, is available in sheets that are usually 36 inches wide. The grit roll is unwrapped and nailed into place with overlapping layers. Roll roofing easily seals areas, such as valleys and roof edges, that are difficult to cover with stiff tile. Composition roll roofing material can be used to cover an entire roof or it can be used in conjunction with shingles.

Considerations

• Other particles that are used to create a gritty-textured, weather-resistant shingle coating are boiler slag, also called coal slag, and ceramic-coated rocks and minerals. Some grit coatings provide additional protection against algal and moss growth. Be aware that grit coatings degrade and particle buildup can occur in gutters, drains, downspouts and along building edges. Some grit coatings, especially those treated with zinc or other moss-preventing treatments have the potential to damage plants and turf located at the roof's drip-line.