TSP Substitute (C) Daniel FriedmanCleaning & Prevention Guide for Algae, Fungus, Lichens, Moss on Stone
Tombstones, Graves, Walls, Sidewalks

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How to clean building stains & algae, fungus, lichens & moss from exterior surfaces:

This article describes cleaning, and preventing future algae, moss, lichens, or fungal growth that occurs on stone, brick, and other surfaces such as buildings, gravestones, sidewalks, stone walls, walks, roadways and in nature.

We discuss how to identify, remove, & prevent algae, lichens, or moss growth on graves, tombstones, stone walls, sidewalks. Photographs of Algae, lichens, moss, mold help identify these substances in nature and on buildings. Photos & text to distinguish among algae, lichens, moss and mold growths on any surface.

We include links to references & researh useful in the identification & control of algae, moss, lichens, and mold.

Green links show where you are. © Copyright 2017, All Rights Reserved.

Methods for Cleaning Organic Growth (Algae, Fungus, Lichens, Moss) from Stone, Brick, or Concrete Surfaces

Photos of Australian tombstone before and after cleaning

Especially if you are restoring artifacts, art works, tombstones, or graves, avoid any aggressive cleaning methods that might damage the roof surface.

Mechanical Cleaning of Brick, Stone or Concrete Surfaces

The gravestone that was shown at the top of this page and appears below in "before and after" photos was successfully cleaned using simply a soft bristle brush and plain water. Here is what Patrick Walsh said about the cleaning procedure:

I only used regular cold tap water, no soap, and a soft bristled dish-brush.

You should wet down and rub in water on the stone by hand (the growths were oily, and repelling water!).

Then brush in circular pattern to break down the lichens, moss, or algae, using plenty of water for lubrication. Hand wipe the gravestone down before it dries again.

Start cleaning the tombstone at the top and work down.

That way you won't have to re-scrub the run-off. This was a 7-foot high grave stone including the cross.

All told, (minus the cross) it took me about 45 minutes (I started on the back, so I would be inspired to do the rest and in case I found a problem.

Then I cleaned the gravestone's sides and top. The front surface was cleaned last.

Photos of Australian tombstone before and after cleaning

Whatever cleaning is done on a stone or masonry surface, make sure the process does not cause more harm than good to the artifact and to the environment around it.

Algae, Fungi, Lichens, Moss: Chemical Cleaning of Brick, Concrete, or Stone Surfaces

Watch out: don't try any cleaners or preservative treatments on a valuable cultural artifact or art work without first discussing options with a professional art conservator. If you are proceeding to use any cleaning procedure or chemical, try it first on a small, unobtrusive area of your artifact or surface.

A comprehensive survey prepared by Caltrans ( 2011) examined studies by various U.S. states concerned with the control of moss growth on pavement. Those experts examined a wide range of methods used to remove moss growth as well as to control or prevent its recurrence, yielding advice on the effectiveness and costs as well as safety of various approaches from which we include excerpts here.

The Caltrans information is followed by advice from the USDA on controlling sooty molds appearing on exterior surfaces.

Treatment Options for Algae, Fungal, or Moss Growth on Stone & Masonry Surfaces

These moss cleaning & control methods studied for application on roadways in the U.S. may be applicable in whole or part to treatment & control of algae, lichens, moss and even fungi on exterior surfaces such as masonry or stone walls, walks, and monuments outdoors

Moss Treatment Method Description Comments
Synthetic moss growth control products Wet & Forget. This commercial product can be used in residential and commercial applications. Marketed as noncaustic, nonacidic and safe for all outdoor surfaces, the product’s active ingredient is alkyl dimethyl benzyl ammonium chloride . Environmental concerns;
Glyphosate. Two applications per year of this herbicide should be adequate to kill the moss. Glyphosate is the active ingredient in commercial herbicides such as Roundup® May not be suitable for areas of animal or human occupancy or direct-contact; Environmental concerns;
Natural-based moss growth control products

Acids: acetic acid, citric acid, pelargonic acid, cloveoil, corn glugen meal were cited by Caltrans as under study, generally less effective and more costly than the synthetic alternatives.

Baking soda, vinegar, biodegradable fatty acids. Certain kinds of soap and borax are also recommended.  

Electrolyzed water: Identified as a cost - effective and environmentally friendly alternative that can be used as a contact fungicide on plant surfaces and for general sanitation in greenhouses.

A cell electrolyzes water, resulting in two types of water possessing different properties:

An electrolyzed basic solution that has strong reducing potential and can be used as a cleaning solution.

An electrolyzed acid solution with a strong oxidation potential that can be used as an alternative to chlorine - based compounds for killing bacteria.

Recent procedure, uses water and saturated salt (sodium chloride) to create an electrolyzed acid used as a contact fungicide on plant surfaces
Mechanical moss removal methods High - pressure, low - volume power washer. A small - scale test of this mechanical method involves the use of a portable power washer to determine how much pressure is needed to remove moss when moving along at a reasonable rate of speed (that is, 10 mph).

Watch out: as we also cite at STAINS on STONE, STUCCO DIAGNOSE & CURE, Grimmer (1992), - Schierhorn ret. 2014) and other experts warn about using abrasives to clean stone exteriors of buildings or stone cultural artifacts. .

Brooming - sweeping has been used on roadways.
Moss cutting machine. This machine, used by an irrigation district in Oregon to remove moss from canals, applies similar technology
Light & Heat to kill, remove or prevent moss growth Infrared heaters. An infrared heater is used to direct a propane flame at a ceramic or metal plate, which radiates heat onto the moss. Other applications use water and intense heat in an enclosed space  
UV light: shielded high-intensity ultraviolet light has been used to treat moss growth on roadways.

Widely used in water treatment & in forensic investigation.


Coatings to retard moss or algae growth on surfaces

Fog line paint: Caltrans observed that the paint used to provide white fog lines along roadways appeared to be a moss growth retardant in areas where otherwise moss appeared along roadway sides and suggested the paint might be moss-retarding.

In our [DF] opinion an error in this consideration was the omission of the moisture-absorption effects of the fog line painted along roadways.

By coating the roadway surface the pavement will surely absorb less moisture and perhaps fewer spores as well, acting thus as a moss growth retardant in an effect beyond the biocidal effect of the paint itself.

This observation suggests that where other conditions permit, periodic coating of some stone surfaces with moisture repellants such as Thompson's water seal may retard moss, algae, lichens ane even fungal growth on those areas.

However in our personal experience those silicone-based coatings are not durable and may need annual re-application, making them not cost-effective for some cases. And on hard surfaces such as walkways there may be slip hazards as well.

Paints including fungicides may use elemental zinc or other metals or chemicals.

Not suited for artifacts, most building exteriors, most walkways, masonry stairs, etc


Laser Cleaning of Sandstone or Stone Surfaces

Building & stone artifact conservators have researched and used lasers as a method for cleaning some stone surfaces. See

  • Dajnowski, A. "Laser cleaning of the Nickerson Mansion: The first building in the US entirely cleaned using laser ablation." In Lasers in the Conservation of Artworks: Proceedings of the International Conference Lacona VII, Madrid, Spain, 17-21 September 2007, vol. 3, p. 209. CRC Press, 2008.

See additional sandstone cleaning citations at



Adapted to include excerpts from

  • CTC & Associates LLC, "Environmentally Friendly Elimination of Moss from Open-Graded Asphalt Pavement", Requested by Deborah Harmon, Caltrans District 1 April 14, 2011, retrieved 3/28/2014, original source: investigations/docs/elimination_of_moss_pi_04142011.pdf

References on building or monument moisture control, moss, historic preservation

  • Bruhns, Harry R., Philip Steadman, Horace Herring, Sarah Moss, and Peter A. Rickaby. "Types, numbers, and floor areas of nondomestic premises in England and Wales, classified by activity." Environment and Planning B 27, no. 5 (2000): 641-666.
  • Christopher, D. "Exterior Cleaning of Sandstone Buildings in Edinburgh: Technical and Aesthetic Considerations: Submitted for the Degree of Master of Science [Architectural Conservation]." PhD diss., School of Architecture, Edinburgh College of Art/Heriot-Watt University, Edinburgh, 1990.
  • Clifton, JR, ASTM STP935 Cleaning Stone and Masonry, Abstract:

    January 1986STP935-EB - Describes modern techniques, methods and materials for restoration cleaning of building facades. 9 peer-reviewed papers examine cleaning practices in the U.S., the selection of appropriate cleaning materials and methods, methods for determining the effectiveness and possible damage caused by cleaning, and cleaning case studies.

    Available from
  • Dajnowski, A. "Laser cleaning of the Nickerson Mansion: The first building in the US entirely cleaned using laser ablation." In Lasers in the Conservation of Artworks: Proceedings of the International Conference Lacona VII, Madrid, Spain, 17-21 September 2007, vol. 3, p. 209. CRC Press, 2008.
  • Griffin, P. S., N. Indictor, and R. J. Koestler. "The biodeterioration of stone: a review of deterioration mechanisms, conservation case histories, and treatment." International Biodeterioration 28, no. 1 (1991): 187-207.
  • Grimmer, Anne E. Keeping it clean: removing exterior dirt, paint, stains and graffiti from historic masonry buildings. DIANE Publishing, 1992.
  • Grimmer, Anne E. Dangers of Abrasive Cleaning to Historic Buildings. [Department of the Interior], Heritage Conservation and Recreation Service,[Office of Archeology and Historic Preservation], Technical Preservation Services Division, 1979.
  • Halim, Al-Hafzan Abdullah, Siti Norlizaiha Harun, and Md Yusof Hamid. "DIAGNOSIS OF DAMPNESS IN CONSERVATION OF HISTORIC BUILDING." Jurnal of Design+ Built 5, no. 1 (2012).
  • Hui, Sam CM, and Anfernee HM Leung. "Sustainable building services systems for historic buildings." In Proceedings of the Joint Symposium 2004: Servicing Dense Built Environments, vol. 16, pp. 133-142. Organising Committee of the Symposium., 2004.
  • Lazzarini, Lorenzo, and Marisa Tabasso Laurenzi. Il restauro della pietra. Cedam. Casa editrice dott. Antonio Milani, 1986.
  • Lisci, Marcello, Michela Monte, and Ettore Pacini. "Lichens and higher plants on stone: a review." International biodeterioration & biodegradation 51, no. 1 (2003): 1-17.
  • Park, Sharon C. "Moisture in historic buildings and preservation guidance'." Moisture Control in Buildings 18 (1994).
  • Piervittori, R., O. Salvadori, and A. Laccisaglia. "Literature on lichens and biodeterioration of stonework. I." The Lichenologist 26, no. 02 (1994): 171-192.
  • Preston, John. "The surface restoration of buildings–An investment in the present as well as in the future." Structural Survey 7, no. 4 (1989): 450-460.
  • Richardson, B. A. "Control of microbial growths on stone and concrete." In Biodeterioration 7, pp. 101-106. Springer Netherlands, 1988.
  • Sáiz-Jiménez, Cesáreo. "Biogeochemistry of weathering processes in monuments." Geomicrobiology Journal 16, no. 1 (1999): 27-37.
  • Sargent, Karen. "Exterior sandstone restoration of Alexander Hall." In Preservation and restoration of cultural heritage: proceedings of the 1995 LCP Congress, Montreux, 24-29 September 1995= Conservation et restauration des biens culturels: actes du congresLCP 1995, Montreux, 24-29 septembre 1995, pp. 231-234. Laboratoire de conservation de la pierre, 1996.
  • Schierhorn, Carolyn. "Sandstone." [PDF] retrived 9/23/2014, original source:
  • Schnabel, Lorraine. "The treatment of biological growths on stone: a conservator's viewpoint." International biodeterioration 28, no. 1 (1991): 125-131.
  • Tiano, Piero. "Biodegradation of cultural heritage: decay mechanisms and control methods." In Seminar article, New University of Lisbon, Department of Conservation and Restoration, pp. 7-12. 2002. [PDF]
  • Tudor, Phoebe B., Frank G. Matero, and Robert J. Koestler. "A case study of the compatibility of biocidal cleaning and consolidation in the restoration of a marble statue." In Biodeterioration Research, pp. 525-533. Springer US, 1990.
  • Unterwurzacher, Michael, Ulrich Obojes, Roland Hofer, and Peter W. Mirwald. "Petrophysical properties of selected Quaternary building stones in western Austria." Geological Society, London, Special Publications 333, no. 1 (2010): 143-152.
  • Wakefield, R. D., M. Young, K. Tonge, and D. Urquhart. "Effects and efficacy of some masonry biocides applied to Scottish sandstone in the control of biological growths: current studies." In Conservation science in the UK: preprints of the meeting held in Glasgow, May 1993, pp. 15-19. James & James Science Publishers Ltd., 1993.

Not all roadway moss control measures in the original source are included in the table above. For example we exclude "Pavement mix selection" as a means of moss control as it pertains more narrowly to roadways not to other outdoor surfaces such as stone walls and brick structures.

Using UV light in a wide range of applications inculding the control of bacteria, mold, and algae or moss growth is also discussed at


The USDA has published How to Recognize & Control Sooty Molds. That publication includes suggestions for removing sooty black molds (the author considers Cladosporium sp. and Aureobasidium sp. as sooty black molds though they may in fact be brown or black and may not easily wipe off as "sooty" molds). Excerpting & commenting on the USDA advice for controlling sooty molds on surfaces: :

Sooty molds can be indirectly controlled by reducing populations of sucking insects that excrete honeydew.

Outdoor furniture can be hosed down with water during periods of honeydew excretion, particularly during drought. The growth of sooty mold fungi is inhibited by preservatives used in treated wood in rustic outdoor furniture. Here is the recipe for a good cleaning solution for removing sooty molds from plastic or painted surfaces:

USDA Stone Cleaning Agent Formula

Powdered household detergent 1/3 cup
Household liquid bleach 1 quart
Trisodium phosphate 2/3 cup [note: for environmental reasons TSP is no longer used, try a TSP substitute]
Water 3 quarts

Watch out: Be sure to wear rubber gloves when cleaning with this solution. [Note that trisodium phosphate is no longer used as a cleaning agent because it is an environmental contaminant.

However substitute products may be available. Be careful not to add a cleaning agent to bleach that can cause production of toxic chlorine gas.


Power Washing Brick, Stone, Concrete Surfaces to Remove Algae, Fungi, Lichens, Moss

Power washing, using plain water or perhaps a deck cleaner can be very effective for cleaning off stone, concrete, or masonry sidewalks and some building surfaces where valuable artifacts are not involved. First be sure that the surface to be cleaned is sound and secure - both to avoid causing serious damage and to avoid rocketing a piece of stone or brick into someone's eye during power-washing.

We have had some trouble with this method, however, when power-washing dry-laid brick and stone walks. The power washer wanted to also remove sand between the bricks or even to lift them out of place. Work carefully, and at a high angle to the surface to be cleaned if you have this problem.

Watch out: don't power-wash antique brick without first testing your procedure. If you sand-blast or use high pressure washing on soft brick or other masonry surfaces you may cause irreparable damage. In freezing climates, blasting the original glaze off of a brick surface means that it will absorb more water, grow more moss or lichens faster, and suffer more freeze damage than ever.

Also be careful when power-washing not to blast water into building wall or roof cavities where you risk cosmetic or even costly mold damage.

Do-it-yourself Cleanup for Algae or Fungal Stains on Stone, Brick, Concrete Surfaces

TSP Substitute (C) Daniel Friedman1 teaspoon of trisodium phosphate equivalent + 8 tbsp bleach in 1-1/2 cups water. (Oxygen bleach is readily available [Sodium percarbonate], which can be mixed with about anything that is not reactive to oxygen and it is not toxic.)

In greater proportions, reader Norman reports using 1 cup of trisodium phosphate, one gallon bleach and 4 gallons water on his own roof and ... "it has worked just fine, spraying it on lightly, then rinsing thoroughly with water about 15 minutes later."

Don't use the original TSP (tri-sodium phosphate) cleaner - it is an environmental contaminant. TSP substitutes such as the product shown (at left) are available at building supply stores and hardware stores.

Some deck cleaning sprays such as Stainhandle® roof and deck cleaner are also sold for use as cleaning solutions for stained roofs and might work on other surfaces - check with the manufacturer. We discuss removing stains from roofs separately

Cleaning Procedures for Marble Surfaces

Procedures for cleaning marble surfaces in or on buildings are at MARBLE CLEANING METHODS

Preventing Algae, Lichens, Mold Growth on Gravestones & Other Stone, Brick, or Concrete Surfaces

Mossy roof cleaned by copper runoff (C) Daniel Friedman

Trim back trees whose branches overshadow the stone surface if it is possible to do so without compromising the aesthetics of the site. Keep the flat or low-slope stone surfaces clean of organic debris like leaves or pine needles which may collect in valleys or at other roof locations.

Chemical sealants or treatments may be permitted for some stone surfaces outdoors, though where we have tried clear silicone water-resistant coatings outdoors they were not very long-lasting.

The New York Times reported that for the Angkor Wat historic Hindu temple, Dr. Warscheid devised a biocide "melange d'Angkor" that was to be used to whiten parts of the temple and to retard the blackening effect of the cyanobacteria or fungi causing the blackening of that stonework.

Watch out: Don't put slippery sealants or coatings on a walking surface.

OPINION-DF: for some artifacts it may be possible to reduce, prevent, and even "kill off" existing algae, fungal growth, or lichens on stone surfaces by installing a zinc or copper strip or cap in a position that sends dissolved copper salts down the surface in wet weather.

We have seen the success of this approach on building roofs where copper flashing was installed (photo of copper-flashed chimney on an otherwise mossy wood shingle roof at left), or where anti-fungal/moss/lichens metal strips were added.

Watch out: don't try any cleaners or preservative treatments on a valuable cultural artifact or art work without first discussing options with a professional art conservator.

Also, as the Times reported in 2008, there was no point in coating the entire Hindu Temple of Angkor Wat with biocide, since within a decade experts anticipated that the fungi or cyanobacteria present would simply adapt to the chemistry of the biocide treatment. Rather, routine cleaning and maintenance were called-for.

This article series tells readers how to identify, evaluate, remove or prevent stains on building surfaces.

Using UV Light to Prevent Moss & Algae or Mold Growth on Masonry Surfaces

Reader Question: How to control moss growth in a historic building tunnel

I hope you may be able to help me.... I've been speaking to a client who has a very old historic building and they lit the tunnels beneath the structure a few years ago (not by me). They are experiencing growth on the stone walls (sample photo attached) which is causing them concern and we think is related to the lighting, which is LED.

It could be also down to the fact that there is now a lot of human traffic passing through the tunnels (thus creating moisture I guess). I'm not a plant expert (or anything even remotely like one!) but I understand that while plant growth can be stimulated using a combination of far red and UV lighting - hence the High Pressure Sodium lighting used for the purpose, that UV can be utilised to kill algae (or prevent growth).

The chap on site says it's more like a moss than an algae but I think moss is different, so really I'm wondering if you know of any ways of preventing moss growth using artificial lighting. It's a Listed Building so it can't be treated with chemicals, we just need to prevent any additional growth if possible and ideally, kill whatever is there.

Sorry, I realise this might take a combination of my knowledge of lighting and yours on horticulture but my Googling hasn't come up with any answers! Thanks very much in advance. Best regards - L.P., West Yorkshire, England 3/28/14


At STAINS on STONE, STUCCO DIAGNOSE & CURE we discuss moss and algae on stone as well as other "stains" such as from fungi and in this article above STONE CLEANING METHODS we discuss methods that can be used to clean and remove such materials while respecting the surface or artifact being cleaned.

I don't agree that because a building is historic that no steps whatsoever can be taken to address moss growth on its surfaces; conservators have dealt with these problems for a very long time and have advice on least-invasive methods that still clean and protect the surface.

In this article I'm adding some helpful citations found by my research in an effort to answer your question, from which I excerpt the following:

Of several surface treatment methods used to control moss growth there are these that you might consider

1. Wet & Forget. This commercial product can be used in residential and commercial applications. Marketed as noncaustic, non-acidic, and safe for all outdoor surfaces, the product'sactive ingredient is akyl dimethyl benzyl ammonium chloride

2. Natural based products including products that contain citric, acetic or pelargonic acid; clove oil; and corn gluten meal have been included in trials conducted by other agencies. Results, where available, indicate that these products are generally less effective than synthetic alternatives and tend to be more costly to apply.

3. Electrolyzed water. This relatively new process uses water and a saturated sodium chloride solution to create an electrolyzed acid solution that can be used as a contact fungicide on plant surfaces

Also listed but not something I'd try indoors or in a traffic area is Glyphosate. Two applications per year of this herbicide should be adequate to kill the moss. Glyphosate is the active ingredient in commercial herbicides such as Roundup

Two mechanical methods are listed for removing and controlling future moss growth on surfaces such as the stone tunnel that you describe, two of which might work in the case you mention:

1. power washing or use of a "moss cutting machine" (not useful for your case)

2. Shielded high - intensity ultraviolet light. This light source might burn off moss or delay its growth by triggering a negative phototrophic response. This method is used to treat recirculating water in greenhouses to remove algae and fungi.

Heat is also listed as a moss control measure:

1. Infrared heater. An infrared heater is used to direct a propane flame at a ceramic or metal plate, which radiates heat onto the moss. Other applications use water and intense heat in an enclosed space.

It seems to me that an initial effort to clean and treat the surfaces combined with UV light might be the approach of choice. 

If it were possible to add heat and reduce the moisture level in the tunnel I'm reasonably confident that the moss problem will be controlled.

If we are not able to make the tunnel more dry, that is if it stays cool and wet, I suspect that a combination of UV lighting and some environmentally-friendly topical treatment may be needed.

Some of the "environmentally-friendly" methods discussed by Caltrans were not economically feasible for highway roadside moss control is needed but might be economically acceptable in a smaller more controlled area such as the tunnel you describe.

Keep us posted, as what we learn will assist others. DF

How to Remove Paint From Stone Surfaces

Please see BRICK SURFACE PAINT REMOVAL as those methods pertain also to stone surfaces.


Continue reading at LICHENS on STONE SURFACES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.



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