Why Are There Black Spots on My Driveway?

Estimated reading time 8 minutes

If your driveway has started to show its age, you may have noticed black spots appearing on its surface. Found on concrete driveways occasionally and stone driveway surfaces more frequently, black spots can spread fast and turn a driveway into something extremely unsightly. Left untreated, they can start to cause damage to the surface that could cost substantial sums to repair.

In this edition of our blog, we look at driveway blackspots, whether you can stop them and how you treat them.

What are the black spots on my driveway?

Black Spot, also known as lichen, is an organism that thrives on a host of surfaces. Finding damp or shaded areas as a home, these black spots attach themselves to the surface and spread fairly rapidly. Where you can often maintain a concrete driveway or other driveway surface relatively easily, black spot or lichen proves to be stubborn and sticks to the surface with intent. Where a simple wash may move some stains or marks away, lichen has other ideas! Consisting of two different organisms, the black spot has one part that deals with the typical photosynthesis processes and another part that has the fungus properties that allow it to stick to its desired surface. The fungus plants itself deep into the driveway sticking to the ground where it forms what is known as a crustose growth. It remains flat and coated in a protective layer, making it almost impossible to remove from the driveway.

What causes the black spots on my driveway?

The black spots that are now taking over areas of your driveway will form thanks to a combination of factors. Certain types of algae will naturally exist in the environment but where they choose to settle and grow depends on whether a hospitable environment can be found. Damp, porous, shaded surfaces are ideal for black spot, and driveways often tick these boxes. Natural stone for example is permeable, as is concrete, and this gives the lichen a perfect base to thrive and breed.

What driveway surfaces are affected by black spot?

Black spot can find a home on almost any surface as long as the conditions are right for it to thrive. We’ve already mentioned concrete being a particular driveway type of choice although it is not likely to be the prime destination.

Lichen grows faster when it’s on a surface it can easily penetrate. Limestone and sandstone for example are two types it loves to call home. A resin-bound driveway is less likely to be chosen by black spot, but it does happen, just like with tarmac driveways. Neither is the first choice but if there is nowhere else for it to settle, it may pick either of these as a base. When it comes to concrete driveways being affected, it is important to look at how the concrete is being used. Wet-cast products that have a low cement content will attract more lichens than concrete driveways that have a high level of cement in their production.

What are the effects of black spot on my driveway?

Black spot causes significant problems if not treated. Damage can range from its unsightly appearance to surface damage that could cost significant sums to repair.

Perhaps the first problem to think about is the aesthetic appearance of the driveway. These unsightly black spots can certainly make your driveway look ugly and really hinder the kerb appeal of the property. Something well worth thinking about if you are considering a sale in the near future.

It isn’t all about how things look though. Without treatment, the black spots will continue to grow and as their roots drive into the surface, they can cause damage to the surface and weaken it. Left even longer, the weakened surface will be compromised as the spread increases. This can lead to cracks and chips in your driveway as well as some areas being significantly weaker than others.

It can be a slow process; the damage will not be noticeable right away, but immediate treatment will stop the spread and save your driveway from extreme damage and costly repairs.

In addition to the cosmetic damage it will cause, and the structural damage that may occur, black spot can also make your surface slippery when wet and a little more dangerous to walk on.

How to identify black spot?

Before fearing the worst and assuming black spot has taken over your driveway, it may pay to check whether these marks on your driveway are this invasive algae or something a lot easier to deal with.

Black spot appears as dark circles or patches on the driveway and will normally be black or dark green. They will be in the most shaded areas or those that see the least sunlight as well as parts of the drive that may get damp. You’ll notice that whereas with moss, weeds or oil a clean-up can be quick and easy, blackspots won’t budge. They stick to the ground and protected by the tough outer layer that surrounds them. This means you may need to adopt more aggressive treatments to get your driveway back to how it should be.

How to treat black spots on a driveway

There are various ways you can treat black spot on a driveway, but much depends on how severe the infestation has become. If the black spot has only recently started to appear, you may be able to treat it with some quick and easy solutions.

A mild detergent and some warm water, scrubbed into the effective area can help remove it or lighten the darkened area. This will only work if the black spot is in its infancy though. At this early stage, you could also consider vinegar and water. The acid within the vinegar can break down the black spot and then make it easy to clean off with detergent and water.

Some driveway types can withstand the force of a pressure washer, but you should always check with the surfacing specialist who installed your driveway before you attempt this. If you were to use the washer on a surface not suitable, you could cause permanent damage to the driveway. Even with drives that can be treated with pressure washers, caution is advised. If you were to use incorrect settings on the pressure washer, you could damage your driveway.

Removing black spot with bleach

For more stubborn cases of black spot, you could look to use Sodium Hypochlorite. However, much like with the pressure washer, you should check whether your driveway surface is suitable for the use of this chemical. You may need to mix it in a 1:10 bleach/water ratio to keep it safe enough to kill the lichen and protect your driveway but you can gradually alter the ratio for stubborn infestations.

When applying the chemical, you should look to treat the whole driveway and not just the infected area. This way you remove all traces (hopefully!) and avoid having those unsightly patches where parts of the driveway appear clean, and others appear dirty.

To apply the Sodium Hypochlorite to the drive, use a bristled brush to help break up the lichen. Don’t be surprised if it doesn’t appear to vanish right away though. This stubborn surface invader may take three or more treatments before it is gone.

Can I prevent black spots from returning to my driveway?

If your treatment has been successful, you will almost certainly not want it to appear again. Unfortunately, there is no cast-iron guarantee you will keep it at bay forever.

Perhaps the simplest way to reduce the chances of black spot returning is by keeping your driveway well-maintained and clean. Removing leaves and other debris will certainly help, as will a monthly deep clean with the pressure washer (if suitable) or a Sodium Hypochlorite and water mix. You could investigate whether it is possible to reduce the amount of moisture present on the driveway or improve the drainage. Starving the lichen of one of its key growth sources is more likely to stop it from finding a home on your drive.

If your driveway has suffered from a black spot infestation for some time and none of your attempts to tackle it have worked, it could be time to consider a new driveway. Especially if the lichen has caused severe damage that could see the driveway develop cracks, splits and holes. Tidey & Webb are the surfacing specialists for Sussex, Surrey and Kent. Our expert team transforms any driveway to give it a completely new lease of life. Whether it be for commercial resurfacing or residential resurfacing, Tidey & Webb is the name you can trust for any surfacing project. Contact us today to see how we can help.

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