FAQs on how to identify, remove, & prevent Algae, Moss, Lichens or other stains on stone & stucco surfaces.

This article series explains how to diagnose, remove & prevent stains due to algae, fungal growth, or moss on stones, monuments, & on surfaces of building exteriors or roofs: this article series describes and provide photographs and advice on identifying, cleaning, and preventing algae, moss, lichens, or fungal growth that occurs on stone surfaces such as buildings, gravestones, sidewalks, stone walls, and in nature.

Appearance of Algae, Fungus, Lichens, or Moss on Stone, Stucco, Masonry Surfaces

These questions & answers about diagnosing & cleaning-off & preventing all sorts of stains or growths on stone or other masonry surfaces were posted originally at STAINS on STONE, STUCCO DIAGNOSE & CURE - that's a great place to start diagnosing and cleaning off stains on your stone or masonry surface.

On 2018-08-23 by (mod) - diagnose red stains on stone exterior

Glad to assist. Take some before and after photos and let us see how well that works.

Though it's for a different purpose, we discuss iron stain removers at WATER SOFTENER IRON & SEDIMENT REMOVAL https://inspectapedia.com/plumbing/Water-Softener-Iron-Cleaning.php

On 2018-08-23 by Clare - remove stains on my house

Thank you very much for your swift reply! I will try this. Much appreciated!

On 2018-08-23 by (mod) - rust stains may be from natural iron inclusions in stone or from iron used in construction

Clare

From your photo [shown above] it appears that the two pieces of dark reddish-brown stone are themselves high in iron inclusions. That's the cause of the red stains that are principally below the stone. Rainwater is a solvent because itself the rainwater is low in metals and minerals.

As rain wets the stone it dissolves and leaches out iron that then runs down the stone below to form a red stain.

You might be able to reduce the stain intensity by using an iron removing cleaner but it will return.

You might reduce the rate of return of the iron stain by appying a clear stone masonry waterproofing agent like Thompson's Water Seal - but you'll want to test its appearance first on an unobtrusive location, and you'll need to apply it again every year or so.

On 2018-08-23 by Clare

Hi Thee,

Can you please help me identify what is the cause of the rusting as per the photo attached [shown above]?

The stone is part of the external wall at the front of the house. Many thanks

On 2018-08-22 by (mod) - lichens & moss on brownstone

C: the green stuff looks very much like moss though there may be some green algae present too.

The tan and gray circular growths look like a lichens growth though I'd need to see a sharper enlarged photo to be certain as some fungal growths also appear in that pattern.

On 2018-08-22 by C - green stuff on brownstone in New York City

Please see photo: several years ago the entire facade of this brownstone in NYC was resurfaced. The main body of the house looks like new. The steps and other surfaces surrounding the steps, which were done last, are covered with this stuff you see in the photo.

It appears that this stuff is eating the surface, or rather is in the brownstone material itself.

I suspect this stuff was in the brownstone mix when it was applied. Thank you

On 2017-04-12 by (mod) - red stains on buildings

Thanks Kai, for space and detail we address your question in the article above

at RED or OTHER COLOUR STAINS On Stone Surfaces

On 2017-04-10 by Kai

I'm surprised you didn't mention serratia marcescens.

On 2017-01-15 by (mod) - remove green stains on the outside of our parkhome?

Barry:

It depends on what the stains are.

It also depends on what the outside of your parkhome is made-of, since some cleaners can damage some exterior siding or trim materials.

Algae, for example, is cleaned using an exterior cleaner like a TSP substitute, or a detergent, along with, perhaps, a brush.

I'd be careful about power spraying as that can damage siding or send water into the home's walls, causing more trouble than I want to explain.

On 2017-01-15 by barry

How do you remove green stains on the outside of our parkhome?

On 2016-08-20 by (mod) - bioslime growing on buildings?

Karen,

I would take the exciting news on TV with a grain of salt.

There are numerous art conservation experts who are doubtless working with this problem. I suspect that the "bioslime" is no such thing - or at most a "safe" appellation used by someone who was not sure if they were seeing algae, moss, lichens, or soot - as often what you are seeing is a dark algae or mold or a combination of those plus airborne particulates, soot, debris.

The effects of urban air on monuments and buildings have beeen widely studied.

An underlying problem is that unless you shelter the outdoor monument or building from the air it's just about impossible to keep things from falling onto and sticking onto it.

Our current law and environmental management systems haven't taken this dark bull by the horns.

That leaves the experts deciding on the least-harmful cleaning procedure and then finding money to do it. Longer term, actual damage to monuments is, I agree, at risk.

These are some example research references that address your black bioslime concern;

Black Bioslime Damage to Stone: Research

• [14] "Microbes Eating Away at Pieces of History", Vina Venkataraman, The New York Times, 27 June 2008 p. F3. http://www.nytimes.com
• [15] Allsopp D., Seal K. J. (1986) Biodeterioration of refined and processed materials. Introduction to biodeterioration. (Edward Arnold, London, United Kingdom), pp 51–53.
• [16] Bock E., Sand W., Meincke M., Wolters B., Ahlers B., Meyer C., Sameluck F. (1988) Biologically induced corrosion of natural stones—strong contamination of monuments with nitrifying organisms. in Biodeterioration, eds Houghton D. R., Smith R. N., Eggins H. O. W. (Elsevier Applied Science, New York, N.Y.), 7:436–440.
• [17] Bock E., Sand W. (1993) The microbiology of masonry biodeterioration. J. Appl. Bacteriol. 74:503–514.
• [18] Griffin P. S., Indictor N., Koestler R. J. (1991) The biodeterioration of stone: a review of deterioration mechanisms, conservation case histories, and treatment. Int. Biodeterior. 28:187–207.
• [19] Grilli Caiola M., Forni C., Albertano P. (1987) Characterization of the algal flora growing on ancient Roman frescoes. Phycologia 26:387–390.
• [20] Ortega-Calvo J. J., Hernandez-Marine M., Saiz-Jimenez C. (1993) Cyanobacteria and algae on historic buildings and monuments. in Recent advances in biodeterioration and biodegradation, eds Garg K. L., Garg N., Mukerji K. G. (Naya Prokash, Calcutta, India), I:173–203.

On 2016-08-20 by Karen Hollyman

I just saw on the news that our white marble monuments in Washington, D.C. are being covered by a black bioslime.

They also reported they do not know how to stop it from spreading.

It was CBS This Morning Saturday that I saw the report on. Is there anyway you can help them save our National Monuments?
Thanks for your time and here is hoping and praying you can help.

Comment:

(Oct 9, 2011) جوري اوسي said:
this is beautiful a pohto

Question:

(May 5, 2012) Evelyn Neber said:

Question: Thick black patches that looked like moss, covered the concrete walls and exteriors of the basement access, outside my ground floor apartment.

Last spring, after a HUD inspection of our complex, the basement was cleaned up:they even had some outside workers in white covered suits come and they power -sprayed and cleaned the whole cellar and the outside. The black moldy mossy patches(some were a couple inches in diameter) are gone.

But my almost new through-wall air conditioner which was right up the cellar stairwell has had surges of but black goopy things flying through it onto my carpet and dining/living room.

I also always have black mold spots all over the blades inside the a/c which I try to clean with q-tips but they always come back. I've never experienced anything like this in my life

. Was this black mold ? The superintendent will not tell me. Do I have any rights? Are they responsible to clean my air conditioner? I live in HUD housing. I am disabled, have what is called probable sarchoidosis and suffer from have asthma and allergy attacks. Can you direct me to where I could possibly go to find out if I have any rights in this situation. Thank you.

Reply:

(June 5, 2012) Angela T. said:

@Evelyn Neber:

It's difficult to determine whether or not your particular situation is harmful black mold or algae. Given the black patches were on the building's exterior, my opinion is that it's algae stains and fungal growth. Black mold is typically found on the building's interior (walls, basement structural joists) where moisture and humidity levels are consistently high.

The white coveralls you saw were most likely used to protect the workers from the cleaning chemicals, usually good ol' bleach, from damaging their clothers or irratating their skin.

Your through-wall air conditioner may have been subjected to the high-pressure water washing and algae run-off, hence the surges and intake of algae.

I'm surprised the superintendent or contractors didn't advise you to turn off the a/c and cover it while they performed their work, so that the mechanisms and filters would be protected. With this said, tenants in HUD housing have certain rights that vary from state to state.

For instance, California has the Toxic Mold Protection Act passed in 2001 that requires landlords to disclose mold discoveries to existing or prospective tenants and the remediation methods taken. Your best action would be to contact your local HUD agency to find out your rights relevant to the state you live in.

Moderator said:

Thanks Angela T., your comments are spot-on.

Question: how do I get rid of algae on my river rocks and rose beds?

(July 13, 2012) Theresa Cremona terric1011@gma said:
I have algae coming from my air conditioner in the corner of my concrete home in Florida.

It is green and staining my river rocks in the beds. I have rose plants there.
How do I get rid of the algae.

Reply:

Theresa the article above describes how to clean off algae, but to stop the problem you will need to find and fix the water source - in this case rerouting the condensate drain to a location that doesn't bother your plantings.

Question: white lichens on living roof fireplace stone wall

(Mar 4, 2014) Kristine Creery said:
We recently purchased a home that has a living room fireplace surrounded by a natural stone wall.

A white lichen is growing in some spots, ranging from dime size to fifty cent piece size. We have cleaned the stone and are trying to remove the spots (by scraping with a putty knife - very gently so as not to damage stone).

What is the best way to remove the spots and how do we keep them from growing back?

We want to enhance and seal the stone soon. Thanks so much!

Reply:

Hi Kristine.

I would like to see some sharp photos including closeups. It would be odd to find lichens growing indoors in a home at normal humidity range. Perhaps it's something else like efflorescence?

Question: pink stones on siding when it rains

(July 2, 2015) Ian said:
The outside North facing wall of our house show pink staining when it rains but disappears when dry I am told that this is a fungus. The walls are white Arctic finish
How do I treat this
Thanks

Reply:

Ian:

You're asking this question on a stone stain diagnosis page. Are your house walls stone or some other material? The solution may depend in part on how the walls are built.

There are fungi and also algae blooms that can stain walls pink, but I'm surprised that the stains are only visible when wet. PResuming the walls are painted you might try adding a fungicide to your next paint job.

Question: white crust on our stone house

(Nov 30, 2015) Anonymous said:
Seeba Perincheril
We see a white crust like stuff on our exterior stone work of our house. I think the stone is fake. Our house is South facing and gets lots of sun to that area. What do you think it is and how can we clean that? Thanks

Reply:

Seeba, please search InspectApedia for EFFLORESCENCE to read about what I think you may be seeing.

Use the page top or bottom CONTACT link to send me some photos for further comment.

Question: bright green mold on flagstones

(Mar 20, 2016) Jan Sutherberry said:
My flagstones have only been down for two and a half years in my back garden. Only in the middle area of the garden has bright green mould. Could you tell me what it could be?

Reply:

Jan

Outoors mold and algae will grow freely, as will moss, on hospitable surfaces, moreso in damp, wet, or shaded areas.

...

Continue reading at STAINS on STONE, STUCCO DIAGNOSE & CURE - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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