Slurry seals and asphalt sealing are very closely related maintenance tasks asphalt. Many paving contractors and customers use the two terms interchangeably. The main difference between the two is the additional component in slurry seals; aggregate.
Over time, asphalt breaks down from water and UV exposure and the bond between the aggregate weakens. This is when you see chunks of aggregate crumbling from the surface. Asphalt sealing is simply applying a liquid spray over the damage. Any small depressions will remain across the surface, giving the water a place to pool up again and continue the process. The aggregate in a slurry seal will help to fill in those small cracks and gaps and promote a more even surface. It will not repair large-scale damage.
In fact, there are three different categories of slurry seals depending on the size of the aggregate added to the seal coat. Type I slurry seals contain fine sand aggregates, with diameters less than 2.36mm. This is most commonly used to treat slow-moving and lower traffic areas such as parking lots.
Type II slurry seals have larger aggregate particles with maximum diameters of 6.4mm. The larger aggregate allows the seal to repair minor ravelling and other more advanced states of wear usually found on higher traffic areas such as roads. It would not be recommended to use this slurry seal on parking lots, since the larger aggregate pieces can cause tire scuffing as cars turn in and out of parking spots.
The last type is Type III slurry seals which contain coarse aggregate chunks. These seals are used to compensate for more severe types of surface defects. The large pieces of aggregate can also fill depressions in the surface, thus reducing the amount of water ponding.
We use a Type I slurry seal for our parking lot maintenance.