An overlay is a new section of asphalt that is typically 1.5” to 2” and therefore has structural strength. A sealcoat is an emulsion – a mixture of asphalt oils, water, and particulates that has no strength and will reveal any limitations or structural deficiencies of the surface on which it is placed. A slurry seal is similar to a sealcoat but with aggregates added to the mix, most commonly ¼” (Type 2) or 1/8” (Type 1) in diameter. Sealcoats tend to perform best in parking lots and lower traffic roadways that may require a lot of vehicle turning while slurry seals tend to perform best on higher volume roadways with mostly directional traffic. In general, an overlay often costs 5-10 times the cost of a sealcoat and a slurry seal costs 1.5-2 times the cost of a sealcoat. The right application can depend on many factors including layout, traffic volumes, condition of the existing pavement, the stage of the lifecycle, costs, and other preferences and priorities.