A backyard stone patio can be a homeowner’s dream. But when surrounded by trees and shade, it can also be a dream for mold and mildew. When a homeowner faced the problem of mold and mildew taking over his patio, he called the Ask This Old House team for help. Mason Mark McCullough brought several solutions (of the cleaning variety!) to help restore that bluestone beauty.
What Causes Patio Discoloration?
Patios are exposed to the elements all year long, and in shady, tree-covered backyards, they can become discolored with mold and mildew. This usually produces green, brown, or black streaks and a slippery film. Luckily, there are solutions.
Solution Choices
There are several options for cleaning a backyard patio. Muriatic acid is the strongest option, cutting through mold and mildew quickly, but it’s not great for plants or pets. White vinegar is also an option, but it only works for efflorescence. Bleach is another product that will work on mold, mildew, and algae. All-purpose outdoor cleaners can handle everything the other products can, and more.
These products do need to be cut with water:
- Muriatic acid: 5 parts water to 1 part acid
- Vinegar: 3 parts water to 1 part vinegar
- Bleach: Varies, but around 3 parts water to 1 part bleach
- Outdoor cleaner: Can be used straight
How To Clean a Patio
The exact process might adjust slightly depending on the solution used, the wait time, and the stains. However, this is a helpful overview of the patio cleaning process.
- Remove all of the furniture and plants from the patio area and wet the surface of the patio with the garden hose.
- Mix a small amount of the cleaning solution in the bucket following the manufacturer’s instructions. Use the scrub brush to apply the solution to a small section of the patio. Let it sit for the appropriate amount of time (according to the manufacturer) before scrubbing and rinsing the solution off. Check for discoloration and proceed accordingly.
- Fill the spray bottle with the appropriate amount of water and cleaning solution. Spray the patio surface evenly and avoid spraying the solution onto other surfaces, plants, grass, and anywhere else you don’t plan to scrub.
- Leave the solution on the surface for the appropriate amount of time according to the manufacturer.
- Connect the scrubbing attachment to the pressure washer. After waiting for the solution to dwell, begin scrubbing the patio with the pressure washer. Move the scrubber back and forth and be sure to cover the entire surface.
- Use the scrub brush to reach the edges, corners, and anywhere else the scrubbing attachment can’t reach.
- Rinse the surface with a garden hose. Take note of any areas that might require a follow-up cleaning.
Resources
Using a pump sprayer, Mark applies a multipurpose outdoor cleaner to the bluestone and allows it to sit for a few minutes. Once the solution is set, Mark sprays down the bluestone using a power washer with a surface cleaning attachment.
