How to clean mold or mildew from concrete and stone

Perhaps your area was very humid last year, or maybe it’s always humid where you live. Humidity creates a cozy environment for mold or mildew to grow. Last summer was very humid in Brooklyn. Green mold or mildew started growing on practically every surface, from concrete to stone, to benches and trees! I needed to learn how to clean mold or mildew from concrete and stone.

I watched a few of my neighbors use a solution of diluted bleach which is effective. Then I learned about another method from a Facebook group I am part of, DIY Home Improvement Projects – Wet and Forget (Wet and Forget Moss Mold Mildew and Algae Stain Remover). As bleach can sometimes alter surfaces, I thought I’d give this product a try first.

Mainly, I was looking to get the green off my property as it’s unsightly and makes my house and front area look poorly maintained. Who wants green all over their façade?

The directions for Wet and Forget say to dilute the product with 5 parts water to one part Wet and Forget, and to use a spray bottle (I used an emptied and clean Windex bottle) and spray it on a dry surface.

The mold around my home was on a few surfaces – the front stairs, stone on the home, and the wall around the front of the property.

It took an exceptionally long time to cover a surface with my spray bottle, as I had so many affected surfaces. I am wondering if it would be more efficient to dip a cloth in the solution and coat the surfaces this way instead? Next time.

With about half the surfaces covered, I waited.

Here’s a before picture of stone on the side of my staircase before it was treated:

And here is the same stone about 24 hours after it was treated:

While the bottle doesn’t give any indication of how long it will take, I thought that 24 hours was fairly fast, considering there was absolutely no scrubbing involved.

This product does have its limits, however. On a concrete surface where the mold or mildew was exceptionally bad and the concrete was a light color, even though the green was out, there remained a brown stain. You can see on the next picture that I’ve treated the left side while the right side remains untreated (where it is green), and the treated side turned brown:

On the dark concrete floor, you can’t necessarily see any stain but on the light concrete wall, you see the brown streaks. Still, pretty effective, and quite a difference!

I’m going to give the wall a good scrub next, and maybe use a little bleach or detergent solution. What I really think I’m going to get though, is a power washer, as I’ve been watching videos and, man, they look like fun. 🙂

But all in all, the product did what it said, it removed or rather killed the mold and mildew and removed the unsightly green cast, without any elbow grease and just a few hand cramps from repetitive spraying!