Brief: 

Sealcoat is an asphalt emulsion product that, when applied to existing asphalt surfaces, can protect pavement from oxidation, freeze/thaw effect and harmful UV rays. Sealcoat has been proven to extend the life of an asphalt pavement significantly. 

Detailed:

To fully understand what sealcoat is, you must first understand asphalt pavements and bituminous products.

Asphalt Basics

Asphalt is a combination of coarse and fine aggregates which are then combined with some percentage (usually around 5%) of asphalt cement. Asphalt is widely used throughout the world as a flexible pavement for roads, parking lots and driveways. Because it is an oil-based product, asphalt can be expensive and prices fluctuate with current markets.

Asphalt is a flexible pavement material. This means that as the sub base, or earth below the pavement, shifts and moves the asphalt surface above will reflect these movements. In northern climates like Montana, the freeze/thaw cycle can be detrimental on a pavement surface leading to cracking, heaving, potholes and dips. 

The oils and bituminous material present in asphalt pavement will react to UV rays from sunlight. This is an oxidation reaction, similar to that in ferrous metals. The oxidation will break the flexible bonds within the asphalt cement oil (AC Oil) and lead to brittleness and an off-gray color in the asphalt. Oxidation and degradation of the surface will then lead to hairline fractures or fissures within the pavement, giving water a path to flow through the impermeable surface. 

Sealcoat Basics

Sealcoat is an emulsion, meaning that tiny droplets of AC oil are suspended in water. This emulsion is then enhanced with additives, sand for traction and structure, fibers for reinforcement as well as cutbacks and products that speed the drying time of the product. Emulsion can be applied by a brush, squeegee or a spray applicator. The most common and effective process is to ‘edge’ the pavement perimeter with a brush or squeegee and then spray an even and overlapping coat of emulsion with a hand wand. 

Sealcoat needs to be applied in dry conditions with temperatures averaging 50°F and rising. Once the emulsion is placed on to the pavement surface, the water contained within the sealcoat will begin to evaporate. As this evaporation process takes place ‘curing’ begins in the sealcoat. This curing forms crystalline bonds between the molecules of asphalt cement, silica within the mix and additional additives. When the bonds are set and the emulsion has fully cured, a new thin layer of asphalt will have been added to the surface of the pavement. Through the sealcoating process, a new wearing surface is created on the existing asphalt. This will act like a new, ultra-thin layer of asphalt, sealing in hairline cracks and protecting the pavement below. 

The most effective analogy to use for sealcoat is comparing it to paint on a house. The structural component (the wood or asphalt) is protected from rain, harmful UV rays and additional wear and tear by the addition of the layer of paint (or sealcoat). It is not a permanent fix, but a preventative measure that will ensure that you get the most possible life out of your asphalt pavement.