When and Why You Want to Mill and Overlay Your Parking Lot
As your parking lot ages, even with the most astute maintenance program you are eventually going to need to replace the surface or wearing course.
A well-executed maintenance plan is focused on several factors
- Cost effective longevity
- Safety focus, by eliminating cracks and holes that may cause slip, trips, and falls
- Maintaining a clean and professional appearance in front of and around your business
- A concerted effort to maintain the base and sub-surface structure of your parking lot
The last one may be a bit obscure. The fact is, water is the number one enemy of any parking lot. Everything we do with filling cracks, seal coating, removing weeds, and eventually replacing the surface layer is all to keep water from making its way down into the base layers. If the base structure of your parking lot is protected, when it comes time to invest in a new surface the process can be much quicker and significantly less expensive than if you need to completely rebuild the entire structure.
BlueSky recommends milling and overlaying your parking lot every 20-30 years, depending on how it is used and maintained. A well-executed Pavement Maintenance Plan will help you achieve this longevity.
What is a Mill and Overlay?
Quite simply this is where the surface of your parking lot is removed by mechanical means. Typically, 1”-2” of material is removed and a new fresh layer of hot mix asphalt is placed back.
Milling Machines come in numerous sizes, some small enough to be towed behind a pickup truck and in small, tight places, to 1200 HP behemoths capable of milling a 12 ½ foot wide lane of highway in one pass. These machines have extremely hard “teeth” attached to a rotating drum that grinds and loads it onto trucks to be recycled.
Asphalt is the worlds top most recycled product. In fact, it is 100% recyclable! Per the National Asphalt Paving Association in 2017, more than 99% of the asphalt reclaimed from roads and parking lots was recycled instead of going into landfills.
Would it not be better to just overlay and NOT mill out the old asphalt?
There are options for simply overlaying your parking lot but there are some risks to consider before choosing this path.
Your parking lot was designed and built to a specific design standard
- Curbs have a certain “reveal”, meaning how much of the curb’s face you see between the parking lot and the top of the curb. In many cases this is a regulatory requirement, without milling you run the risk of your property not meeting code. You will need to check with your local code enforcement officials.
- Your parking lot also was designed to move storm and rain water away from your building and either to catch basins or swales to carry the water away. If you choose to overlay without milling, you run the risk of changing the designed flow points. We have seen projects where the contractor did not take this into account and large areas of storm water puddled in the parking lot in areas it had not done so previously. We highly recommend a detailed survey of the entire lot prior to any work, which will allow for proper planning and mitigation of any drainage issues.
- ADA requirements are another factor to consider. As Federal, State, and Local regulations become increasingly more difficult to comply with, by simply overlaying your ADA accessible areas you run the risk of becoming “non-compliant”. As with water drainage concerns, BlueSky recommends a detailed survey of your ADA accessible spaces. Make 100% certain that any work you perform will follow the current regulations.
Remember you are overlaying because the existing surface is no longer structurally sound, it is probably full of cracks, it is well aged, and unsightly. By simply placing a new layer of asphalt over the old, you run the risk of premature failure, reflection cracking, and surface irregularities.
By milling and overlaying you are simply recreating a new surface lay in the same way it was originally designed, you remove the older failed materials and you recycle your old surface.
It is always important to work with a partner you trust, you should be able to inquire to the points above and make an informed decision on what is best for your situation at the time.