Since asphalt is a petroleum-based product, other petroleum products may react with the surface. This includes vehicle oil and gasoline. The sealcoat may act as a temporary barrier against those materials. A sealcoat is not a crack-filling agent; this must be done prior to applying the sealcoat. Sealcoating may also reduce the friction or anti-skid properties associated with the exposed aggregates in asphalt.
There are primarily three types of asphalt sealers. They are commonly known as coal tar, asphalt emulsions, and acrylics. All three have their advantages but are typically chosen by the contractors’ preference unless otherwise specified. Some states in North America have banned the use of coal tar–based sealants primarily based on United States Geological Survey studies.
Pavement sealers are applied with either pressurized spray equipment, or self-propelled squeegee machines or by hand with a squeegee. Equipment must have continuous agitation to maintain consistency of the sealcoat mix. The process is typically a two-coat application which requires 24 to 48 hours of curing before vehicles can be allowed back on the surface. Prior to application the surface must be completely clean and dry using sweeping methods and/or blowers. If the surface is not clean and dry, then poor adhesion will result. Once the surface is properly prepared, then properly mixed sealer will be applied at about 60 square feet per gallon per coat.