Asphalt overlays make up a significant portion roadway paving work done today. The surface preparation for an overlay project is dependent on the condition, type, and elevation of the existing pavement. The pavement should be structurally intact, level, clean and capable of bonding to the overlay. To meet these prerequisites, the existing pavement is usually repaired, leveled, cleaned and then coated with a binding agent.
Here are five factors to consider when determining if an asphalt overlay is a good solution for your parking lot.
1. Size -
The size of the parking lot plays a big role. If a parking lot is small, the preparation work needed to perform an overlay becomes a larger portion of the overall cost. This may result in removal and replacement being a more cost-effective option.
2. Elevations -
The elevations of the existing lot are another factor to consider. Is there room to overlay the lot and still have drainage occur properly? To perform an overlay, there needs to be a 1 ½” minimum of asphalt thickness when done, which means the pavement must either be settled that far or milled down that far to allow the proper thickness. If the pavement has not settled at the building, (and there is no apron against the building allowing room for a mill, a section of the pavement will need to be removed by sawcutting it and repaving it at a lower height in order to then pave the new surface layer flush with the building. Sometimes there is a concrete apron in front of the building, and milling can be done along the joint of the concrete and asphalt.
3. Pitch -
If the parking lot is on the flatter side, the amount of required milling to make a proper joint to overlay increases. If there ends up being a significant amount of milling, it may end up being more cost-effective to simply remove the existing driveway and start from scratch.
4. Cracking -
Any cracking in the existing parking lot will reflect through the new overlay over time. The exact amount of time it will take to reflect varies on surrounding soils in the area. It can take years or can happen the very first winter. The time frame for reflective cracking is an unknown but it most definitely WILL occur. There are paving fabrics that can be applied to the existing surface to slow the reflective cracking, but the effects of freezing and thawing oftentimes will make those cracks re-appear over time.
5. Expectations -
If an overlay is desired, there has to be an expectation of the customer that this method is not as long-lasting as a full removal and replacement. A 15-20 year life on a removal and replacement is common, whereas an overlay may last a shorter time, about 10-15 years. Again, this will vary with soil type. Sandy soil-type areas have well-draining soil and the overlay will have a longer lifespan than loamy/clay soil types that have a tendency to hold water, making it more susceptible to freezing and thawing damage.
If the parking lot has minimal to no cracking, the customer is aware that reflective cracking may occur over time, the drive has good pitch, and the preparation time costs don’t outweigh the removal costs due to driveway size or pitch, it may be a good candidate for overlay. It is important that the customer understands that this is the most cost effective method achieve the look of a new parking lot, as opposed to doing a complete repave.