Ask the Builder: Repairing a shallow blacktop pothole
Q: Tim, I read a previous column of yours in which you talked about repairing a shallow depression in a concrete surface using sand and Portland cement. My issue is I have a few shallow puddles in my blacktop driveway, and I know this ponding water will eventually create a far more serious issue. The normal patching products sold in bags will not work, as the depression is too shallow. I tried using it once and it all peeled up. How do you recommend creating a patch that stays put and matches the rest of the blacktop as closely as possible? I’m 78 years old and quite sure I can follow your directions. —Katie D., Laurel, Md.
A: I have had similar problems. There are three places in my blacktop driveway that have sunk. One of the areas is where the underground electric and cable TV wire pass under the drive. I’m quite sure the contractor didn’t compact the fill in the trench, and/or he used the wrong material. (I didn’t build the house I currently live in.)
Two other locations are probably poor fill as well. Two years ago, I removed all the crumbling blacktop in one of these areas and filled it with 1.5 inches of cold-patch blacktop, with no success. I’ve since had a little more settlement in this area and quite a bit of the cold patch has eroded. In other words, my driveway is the poster child for the problem Katie is facing.
I used an exterior epoxy that’s made to repair concrete and asphalt defects. It can also be used to fill cracks larger than 3/8 inch in concrete slabs. If you were to just use the epoxy to fill the depression, you’d end up with a medium-gray monolithic patch. That’s the color you get when you blend the white epoxy component with the black component. Blacktop is actually a mosaic of different stones, sand and the black asphalt cement holding the stones and sand together. I decided it was really easy to match this look with a minimal amount of effort.
The first step in the process is to stop and read the instructions on the label of the epoxy. Pay attention to the temperature range when you can install it. I decided to wait until the daytime temperatures were in the mid-70s F, and I worked in the shade.
The epoxy components have the consistency of very thick peanut butter. I used a stiff bent 3-inch scraping tool to blend them together on a large thin piece of plywood. I discovered wide side-to-side strokes did an excellent job of thoroughly mixing the epoxy. Don’t try to scoop and turn it over in a large pile as it’s just too sticky to do this.
It’s important to realize that before I even unpacked the epoxy, I gathered up some stones and sand from the edges of my driveway. These things used to be part of my blacktop. Each winter the New Hampshire ice plucks some from my drive. If you don’t have any stones and sand, just take a close-up photo of your blacktop and go to a nearby gravel pit to get matching stones. Trust me, you’ll never regret taking the time to do this.
What I love about this epoxy-repair method is the epoxy can be feathered to just 1/16th-inch thickness. This allows you to make a repair that absolutely gets rid of any puddling. In my case, the thickest part of my depression was about 5/8-inch.
To achieve a permanent bond, you must get rid of any dust from the blacktop as well as any other loose stones. I used my hand-held leaf blower, garden hose and a push broom to do this. I basically washed and rinsed the blacktop and allowed it to dry thoroughly.
I mixed up equal amounts of the epoxy, ending up with about a half-gallon of material. Using the scraper I transferred the sticky goo from the plywood to the center of the depression and worked my way to the edges. I was careful to not put the epoxy outside of the depression. I also made sure the epoxy was about 1/4 inch lower than the other flat portions of the blacktop outside of the depression. The stones and sand would be used to make up the difference.
The epoxy I used has a very long open time. You have plenty of time to work with it after mixing. Looking at the mosaic of stones in my existing blacktop, I started to place larger stones in a random pattern throughout the epoxy. I then scattered smaller pebbles around the larger stones. I was careful to use the smallest pebbles at the edge of the patch.
After all the stones were placed, I then scattered dry sand over everything. I wanted the sand to hide the epoxy. I used a scrap piece of 2x4 to pack the stones and sand into the epoxy and to make sure the new repair was flush with the surrounding blacktop.
I wish now I had purchased black sand, but when you view my patch from a distance only a perfectionist would complain about the light-colored sand.
I created a video for you to watch to see the epoxy I used and how I did the job. Just go to my AsktheBuilder.com website and type “blacktop epoxy repair” into the search engine and you’ll locate it with no issues.
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