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Black stains on building exterior stonework (C) InspectAPedia C&D Sandstone Stain Diagnosis, Cure, Prevention
How to Identify, Diagnose, Clean & Prevent Algae Stains on Sandstone Surfaces

  • POST a QUESTION or COMMENT On the cause, cure, & prevention of algae, fungus, moss or lichens stains & growth on exterior surfaces such as stone monuments, buildings, roofs, & other site features.

Algae, Moss, Lichens or other stains on sandstone surfaces of buildings or monuments:

This article discusses the causes & remedies for dark stains that appear on both natural and cultured sandstone? We address methods for removing stains from sandstone, and we discuss how experts control the development of algae or other stains from forming on standstone in the first place.

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. We include links to references useful in the identification of algae, moss, lichens, and mold. Our page top photograph algae growing on the stone wall at the entry to the dungeon of Goodrich Castle, Ross on Wye, Herefordshire, England U.K.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Cause & Cure for Dark Stains on Sandstone, Re-Constituted Sandstone & Building Exterior Masonry Surfaces

Black stains on re-constituted sandstone on a building exterior (C) InspectAPedia C&D

[Click to enlarge any image]

Reader Question: Having looked on your website I was wondering if you could tell me if you think these black stains on this re constituted sandstone could be bacterial and what damage could this be doing and the best way to treat it. C&D 9/23/2014

Black stains on re-constituted sandstone on a building exterior (C) InspectAPedia C&D ... Black stains on building exterior stonework (C) InspectAPedia C&D

Reply:

Black stains on building exterior stonework (C) InspectAPedia C&DWhile bacteria may be a factor in black stains on masonry-like building exteriors, more often the colour is due to an algae or a fungus. That's what I see in your first three photos of black stains on building masonry exteriors.

At above right I see what looks like moss or algae or both on a brick wall inside corner where one would infer the presence of roof runoff spillage that might be better controlled or routed. But shade is also a factor in moss and algae growth on buildings.

And in our photo at left we see a heavy moss growth on the building balcony edge suggesting a long-standing combination of watr and possibly partial shade in this location.

See ALGAE, FUNGUS, LICHENS, MOSS COMPARED for details.

Sandstone & Other Building Masonry Cleaning Advice for Black Stains, Moss, Algae

We discuss the cleaning/restoration of the stone grave marker shown at page top as well as other stone surface cleanign methods in more detail
at STONE, STUCCO & BRICK CLEANING METHODS.

Watch out: Grimmer (1992) warns about using abrasives to clean stone exteriors, and further quoting another expert on cleaning sandstone:

Avoid the use of nonproprietary acids on sandstone, which can damage the material irreversibly.

Proprietary cleaning materials fall into two categories—general purpose and cleaners for metallic-sensitive masonry. Only cleaners for metallic-sensitive surfaces should be considered.

Always use a test panel and evaluate the re- sults for at least two weeks be- fore determining acceptability. - Schierhorn _ret. 2014)

In addition to reviewing the article above, you'll want to take a look at STONE CLEANING METHODS [live link is given below]

Also see the citations we offer below, particularly Grimmer (1992) and Christopher (1990)

Research on Re-Constituted Sandstone constituents, installation, troubleshooting, cleaning, repair

 


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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

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.


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