Have you noticed black spots appearing on your sandstone patio? Have you tried to rub it off only for it to seemingly reappear in other areas of the sandstone blocks? Don’t be alarmed: those black spots are natural and organic and are treatable. Removing black spots from the sandstone patio isn’t fun nor a quick exercise, but your efforts will be rewarded with a sandstone patio that will look as good as the day it was first laid on your patio.
While sandstone makes for low-maintenance paving material, it does require some sweat to keep clean and in tip-top condition. By regularly sweeping its surface, you will remove surface debris and a few passes with a pressure washer will help even more to keep your sandstone patio looking neat.
However, it won’t prevent black spots from forming on the surface. Those black spots are a common problem, but as we’ve established there are proven methods for removing them. To understand black spots and how to remove them, you first need to know what those black spots are and how they develop before you can treat them.
What are Black Spots on Sandstone Patio?
Sandstone is the most popular kind of paving material used for patios. Thanks to its gritty, rough texture and surface it offers a high level of grip for walking on. What’s more, sandstone is a strong and durable material and it has a beautiful veined surface that adds character to any outdoor area of your home or office.
Sandstone is also porous. It is in those open pores that the black spots develop. In fact, different colors of sandstone rocks have different porous qualities, and it is the lighter-colored ones most popular that actually have the larger pores that enable the black spots to develop in greater numbers.
Those black spots are lichen. It grows most prolifically on the stone’s surface in damp and sheltered areas – and most commonly where your patio is positioned and your patio furniture rests. Lichen forms on the underside of leaves on trees and plants as microscopic spores.
These spores are released by the leaves and carried by the wind to fall on your sandstone paving. You won’t even see the spores until they’re settled and growing in the sandstone’s pores. It takes about two years for lichen to germinate and take root in your sandstone’s layers.
By the time it appears on the surface of the pavers, it has already grown a network of roots to anchor it into the sandstone. As it is an organism, the lichens feed off the minerals in the stone to grow: to reach more minerals, it forms tendrils called hyphae you spot on the surface of your sandstone.
These hyphae eventually and gradually spread over the surface and it sometimes seems like large blotches on the surface and those stones with larger pores only exaggerate the problem to make it seem much larger than it really is.
Ways to Treat Black Spots on Sandstone Patio
There are a number of ways to treat black spots on sandstone patios. While the black spots can seem to be a surface problem, the lichen has in fact anchored themselves into the sandstone’s pores. All ways to remove black spots from sandstone patios require removing the lichen. That can only be achieved with a lot of elbow grease. These are the four ways to treat black spots on sandstone patio:
1. Pressure Washing
Using a pressure washer is an easy and effortless way to target surface hyphae. What it does is it washes off the hyphae to stunt the growth of the lichen, but it won’t kill the lichen. It is recommended to regularly pressure wash your sandstone patio to prevent the spores of the lichen settling into the sandstone’s pores.
2. High-Temperature Steam Cleaning
The goal of using a high-temperature steam cleaning machine is to kill the lichen. The heat nearly instantly kills the lichen, but it won’t remove the black spots.
3. Cleaning Detergents
Your local DIY shop or supermarket will most likely stock a range of soaps and patio-specific cleaning detergents. A bucket of warm water with your chosen detergent and a steel or stiff brush will get into the surface pores and scrub the lichen’s roots loose. As we have already said, this requires a lot of elbow grease, and if your patio is a large area you might find it a daunting task.
By mixing equal parts bleach and water into a bucket will not only kill the lichen as effectively as a high-temperature steam cleaner, but it will also bleach the lichen’s color right out. This method will also not entirely remove the lichen, but over time the stubborn roots of the lichen will free up as it decays for you to brush and sweep it off the surface layers of your sandstone patio.
How to Remove Black Spots from Sandstone Patio
The most effective method to remove black spots from the sandstone patio is to actually combine a few of the above methods. We have a proven process for you to use to return your sandstone patio to its original condition:
Remove all patio furniture and other objects from the patio area. It is recommended you keep your pets away from this area too.
Sweep the patio to rid the sandstone’s surface of any dirt and debris to leave a clean area for you to work with.
Using the pressure washer now will loosen the surface hyphae and open up the pores blocked up by the lichen’s roots. Slowly move over the entire patio area by holding the nozzle of the pressure washer just an inch or so from the sandstone to give this step the best chance at clearing as much of the hyphae away.
Fill your bucket with your chosen detergent and water mixture and use the stiff brush to scrub the sandstone’s surface as deeply as you can. If you use bleach instead, make sure that your pets are kept away from the patio’s area for the following 48 hours. Once you have completed this entire process, it is essential that you water your plants to wash off the bleach that may have splattered onto their leaves and to wash the excess water away from your plants before it reaches their root system.
Allow the detergent/bleach solution 15 minutes to settle into the pores and to kill the lichen’s deeper roots to prevent them from growing more hyphae in the future.
Grab your pressure washer again to once more penetrate deep into your patio’s sandstone pores. The lichen will now be easier to remove from the pores. If you made use of bleach, it will have bleached the color out of the lichens and removed the unsightly black spots but not the lichen and its roots. As you did before, walk the pressure washer slowly over the sandstone to make sure it sprays the water into all the pores.
Allow the sandstone to completely dry before replacing your patio furniture and other objects. Remember, lichen favor damp and shaded areas and the last thing you want is for lichen to regrow there right after you’ve sweated over removing the pesky black spots.
For black spots that have been left to grow unattended by regular cleaning, you may need to repeat steps 1 to 7 in a few weeks if your first pass never removed all traces lichens and their black spots. It is advisable to use your pressure washer two a week for a month or so to remove those dead and decaying lichen and their roots from your patio’s sandstone. This will return your sandstone patio to the condition when it was freshly laid.
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