When you find small, or perhaps not so small, depressions in your driveway it is a sign that there is something fundamentally wrong with the foundation of your driveway.
Causes Of Asphalt Driveway Depressions
Any one of several things, or a combination of things, could have caused this problem.
If your asphalt driveway is relatively new it may well be the contractor who constructed did not compact the underlying foundation gravel correctly. And whilst at the time before he laid the asphalt it may have appeared to be hard if it had not been compacted sufficiently over time it will settle. As asphalt is a reasonable flexible material the surface doesn’t always break up when the depressions occur.
Are there ant workings nearby? If they have managed to get underneath your driveway then they could be the cause of depressions. Your asphalt contractor should have put down an ant killer and an herbicide or soil sterilant before bringing in the gravel. If, however, your driveway is fairly old the ant killer may no longer be effective.
How well does your driveway drain? If water stands at the edges of your driveway or even ponds on it, it may well seep into the foundation layers and cause problems. Poor drainage is one of the most common problems when it comes to failure of the foundation layers.
How To Fix Asphalt Driveway Depressions
As with most things there are several things you can do:
- Do nothing. Ignore the problem and hope it goes away. The problem with this though is over time the depressions will deteriorate and become potholes. These will now require additional effort to fix.
- Buy a bag of cold mix asphalt,
or a similar product, from your local hardware store and patch the depression just as if it was a hole. All you need to do is:
- Neatly mark out the area of the depression. Use a length of timber as a straight edge to see the extent of the area to be patched. When complete the patch needs to be flush with or just above the surrounding surface. An easy way to see how much needs to be patched is to flood your driveway with water. Then, with chalk, mark out those areas where water is ponding.
- Depending on the cold mix asphalt product you buy you may or may not need to put down a bitumen emulsion tack coat. If you do need to put one down your hardware shop will be able to supply it. And to put it on you can use a paint brush.
- Once the tack coat is done put the cold mix asphalt in the depression. Make sure to leave it about an inch higher than the surrounding surface. Then tamp it down with a hand rammer. It is best to try and get it flush with the rest of the surface or slightly higher so that water will not sit there.
- After you have tamped the asphalt patch down it is a good idea to put a coat of asphalt sealer over the top of it as well. The reason for this is cold mix can be porous particularly as it has only been compacted by hand and it is important to keep water out of the gravel layer just below the surface. Your local hardware shop should be able to advise you as to the sealant to use. If you have had to use emulsion as a tack coat then you could use it as a seal coat as well.
- Repair the depressions properly. In other words dig down until you hit solid ground. Square the hole off. Apply ant killer and herbicide and then bring in new gravel and compact. Then patch as described in 2) above.
Obviously the third option is the technically correct option; however option 2 is perfectly acceptable. Just be warned though, you may need to do this operation several times before the depression stops subsiding and you can consider your asphalt driveway to be safe.