Sealcoat

Sealcoating a road on the University of California, Davis campus in 2013.

Sealcoat is a bituminous liquid mixture that is applied to asphalt.

Benefits

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 reduce the friction or anti-skid properties associated with the exposed aggregates in asphalt.

Types

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.^[1]

Acrylic sealers are typically produced in multiple colors and are a niche product for sealing and beautifying properties such as driveways, golf cart paths or as identifiers to specific parking areas or entrances.

Application methods

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.

Polycyclic aromatic hydrocarbons

Some studies that suggest that refined tar sealants are a significant contributor to polycyclic aromatic hydrocarbon levels in streams and creek beds and that the continual application of sealcoats may be a significant factor. As a result, a few municipalities in the United States have banned this material.^[2] The same studies also suggest that it can be harmful if ingested before curing and ingesting soil or dust contaminated by eroded coal tar sealant.^[3] It is also known to have effects on fish and other animals that live in water. Other water based seal coating materials often perform poorly, especially in climates where temperatures drop below freezing point.

References

1. "coal-tar - U.S. Geological Survey Search Results". U.S. Geological Survey. Retrieved 14 July 2015.
2. "Actions to Restrict or Discontinue the Use of Coal Tar-Based Sealants in the United States". Pca.state.mn.us. Retrieved 5 October 2014.
3. "Cancer Risk from Incidental Ingestion Exposures to PAHs Associated with Coal-Tar-Sealed Pavement". Pubs.acs.org. Retrieved 5 October 2014.