Outdoor concrete turning black (algae?)

[mystang52]

I have a concrete, uncovered, front porch. It faces south. Based on Google research it may be "black algae." Not shown, but immediately to left of this picture I have some bushes, and in front of them some flowers. l
Suggestions for best way to get rid of this? I presume some diluted bleach, but if there are other suggestions or effective over the counter products, I'm all ears.

 

[Tom52]

A good pressure washer will make short work of it.

 

[Big_Hitter]

when is the last time you pressure washed it?

 

[Sunset]

Bleach diluted will work great, but it has to stay on for some time. So simply spraying it on does not work too well.

I put newspaper on mine, then soaked the newspaper with bleach.

You might want to do it in late evening so it can sit overnight, as the sun baking on it will dry out even the bleach soaked newspaper quickly.

Also having the newspaper soaked bleach solves the issue of bleach water running off the cement to areas you don't want.

 

[FIREd]

I just used a pressure washer to get rid of it. I never found a way to prevent it from coming back though.

 

[Amethyst]

On a textured concrete surface, the pressure washer can take quite a while to get out the stains. Is there any paint or stain that can prevent the stuff from coming back? Maybe lime paint?

 

[audreyh1]

We have had good with wet-n-forget spray once or twice a year.

 

[mystang52]

Moved into this house May 1985. Last time I pressure-washed it? I don't remember, but if I ever did it was April 1985 or before I sincerely appreciate the tips so far. I think I'll try that bleach/newspaper idea first.

 

[Aerides]

Yup pressure washer. I have a nice simple 200 psi electric one as I have to do our sidewalk at least once a year. I need to try wet and forget to make that less frequent.

 

[aja8888]

Yup pressure washer. I have a nice simple 200 psi electric one as I have to do our sidewalk at least once a year. I need to try wet and forget to make that less frequent.

2,000 PSI instead? 200 sounds too low to be a pressure washer.

 

[mountainsoft]

Suggestions for best way to get rid of this? I presume some diluted bleach, but if there are other suggestions or effective over the counter products, I'm all ears.

You can pressure wash as others have suggested, but unless I have a lot of area to do I find that more trouble to drag out the equipment and hook up the hoses. Not to mention, you can damage surfaces with a pressure washer if you're not careful.

I usually just grab a deck brush on a pole and scrub it with a bucket of cleaner mixed with water. For general cleaning the "30 seconds" cleaner works fairly well. However, it is essentially a bleach product so any splatter will bleach your clothes too.

https://www.homedepot.com/p/30-Seconds-1-Gal-Outdoor-Cleaner-Concentrate-100047549/100120403

I also like ZEP concrete cleaner. I use it once a year or so to clean my garage floor, and occasionally use it outdoors on sidewalks too.

https://www.homedepot.com/p/ZEP-1-Gal-Driveway-Concrete-and-Masonry-Cleaner-ZUCON128/100619236

 

[Aerides]

2,000 PSI instead? 200 sounds too low to be a pressure washer.

ok yeah that lol.

 

[JP.mpls]

FYI: There is a subreddit group called "powerwashing porn", and the whole thing is just photos of before and after power washing work.
The transformations are really amazing.
JP

 

[nvestysly]

We have had good with wet-n-forget spray once or twice a year.

There are several similarly named products... Spray & Forget, etc. Regardless of the brand, I recommend using the type that you spray on, keep wet for as long a possible (10 minutes or so) and then allow to dry in place. The directions indicate that you should not wet the area (hose or rain) for 24 hours.

After that, periodic rains wash away the stains. In less than 8 weeks our sidewalk looks much cleaner! If it's in an area that doesn't get wet with rain you can rinse it once a week or so with a water hose to simulate what the rain would accomplish. For instance, our driveway typically has two cars parked on the concrete so even when it rains the concrete doesn't get very wet. So a week or so ago I moved the vehicles and thoroughly rinsed the driveway with a light scrub of a broom. Looks much better now.

By the way, our neighbor used a pressure washer with a special round cleaning head and it did a great job cleaning the driveway and sidewalk. I inquired and the neighbor indicated after-the-fact they would not recommend doing any pressure washing as it removes a layer of concrete. Their driveway and sidewalk is much more rough after using the pressure washer.

 

[Amethyst]

Some people enjoy making elaborate designs on dirty driveways with pressure washers. I thought that's what you meant at first ;^>

FYI: There is a subreddit group called "powerwashing porn", and the whole thing is just photos of before and after power washing work.
The transformations are really amazing.
JP

 

[always_learning]

We have had good with wet-n-forget spray once or twice a year.

This is great stuff.

FYI: There is a subreddit group called "powerwashing porn", and the whole thing is just photos of before and after power washing work.
The transformations are really amazing.


JP

It's amazing how satisfying it is to watch the dirt just wash away in those videos.

There are several similarly named products... Spray & Forget, etc. Regardless of the brand, I recommend using the type that you spray on, keep wet for as long a possible (10 minutes or so) and then allow to dry in place. The directions indicate that you should not wet the area (hose or rain) for 24 hours.

After that, periodic rains wash away the stains. In less than 8 weeks our sidewalk looks much cleaner! If it's in an area that doesn't get wet with rain you can rinse it once a week or so with a water hose to simulate what the rain would accomplish. For instance, our driveway typically has two cars parked on the concrete so even when it rains the concrete doesn't get very wet. So a week or so ago I moved the vehicles and thoroughly rinsed the driveway with a light scrub of a broom. Looks much better now.

By the way, our neighbor used a pressure washer with a special round cleaning head and it did a great job cleaning the driveway and sidewalk. I inquired and the neighbor indicated after-the-fact they would not recommend doing any pressure washing as it removes a layer of concrete. Their driveway and sidewalk is much more rough after using the pressure washer.

We used one of the spray & forget products on our brick walls to get rid of mildew caused by rain runoff and that stuff was amazing. Our neighbors used it on their shingled roof with the same results.

Oddly, I never thought of using it on sidewalks and driveways.

Our neighbor also had excellent results with the rotating brush head on his pressure washer.

 

[Ronstar]

I pressure wash mine and it looks brand new when I’m gone. Think I’m go to spray wet n forget on it. It works great on shingles and vinyl siding

 

[Walt34]

I'm in the pressure washing group, I like the brute force aspect of it. Kinda hard to argue with 4,000 psi of water.

 

[nvestysly]

There are several types of the Spray & Forget products...

Some work in a matter of minutes and must be rinsed off, some you let dry in place, some for concrete, some for shingles, etc. Pay attention to which version you are buying.

 

[GreenEggs]

I pressure wash mine and it looks brand new when I’m gone. Think I’m go to spray wet n forget on it. It works great on shingles and vinyl siding

Good to hear about it working well on shingles.

 

[REWahoo]

Good to hear about it working well on shingles.

Sounds like it might be preferable to some of the side effects we hear about from the Shingrix vaccine...

 

[Chuckanut]

I have a quick question about Wet and Forget.

Can it be used on painted wood surfaces such as my deck?

It would solve a big problem if I could. Thanks.

 

[Ronstar]

I have a quick question about Wet and Forget.

Can it be used on painted wood surfaces such as my deck?

It would solve a big problem if I could. Thanks.

Label on the back of the container says "painted surfaces".

 

[NewEnglander]

I use Wet & forget on the side of my house , deck and painted deck rails, stone sidewalks. No issues with painted surfaces. I caused more damage with the power washer before I discovered Wet & Forget. Love the stuff, I bought a backpack sprayer so application is so simple. I found that Zoro.com has the best price for it. If you buy 2 gallons of concentrate the shipping is free.

 

[Winemaker]

If you use commercial mulch, especially the black colored mulch, the problem is artillery fungus, and it is the source of your problem. It is a royal PIA to get rid of, eliminate and control. I thought I was doing my mom some good around her house and now have more work to do.