Cleaning & Prevention Guide for Algae, Fungus, Lichens, Moss on Stone Tombstones, Graves, Walls, Sidewalks
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How to clean graves, tombstones, stone walls, sidewalks
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
We provide photos and text to help distinguish among algae, lichens, moss and mold growths on any surface.
Questions & answers about the best methods to clean stone surfaces
How to clean exterior stone surfacaes: This article describes cleaning, and preventing future 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.
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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.
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.
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.
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). Quoting:
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:
Powdered household detergent
Household liquid bleach
Trisodium phosphate
Water
1/3 cup
1 quart
2/3 cup
3 quarts
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
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
1 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 StainhandleR 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 at Black Stain Removal & Prevention.
Preventing Algae, Lichens, Mold Growth on Gravestones & Other Stone, Brick, or Concrete Surfaces
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.
Online Guide to Types of Stains on Building Surfaces:
In the following guide we list types of stains by stain color & appearance, by building location or material, and by stain cause. We distinguish among the following stuff that may stain or be found growing building roofs, walls, or other surfaces, with extra focus on asphalt shingle roofs as well as other roofing materials such as wood shingles, wood shakes, roll roofing, and even slate or tile roofs. Some of these types of roof stains or discoloration are only cosmetic in nature, while others may indicate growths that are likely to reduce the roof covering life. A more detailed, illustrated version of the list below is given at STAIN DIAGNOSIS on BUILDING EXTERIORS.
Black stains on asphalt roofing products such as asphalt shingles or roll roofing, caused by extractive bleeding (product defects) - see Bleed-Through and see Roofing material defect / environmentally-caused roof shingle stains.
Black, brown, or gray stains on roofing products due to debris left on the roof surface, such as piles of leaves and organic waste from nearby trees. See Debris Staining and see Proximate cause roof shingle stains
Black or other colored stains on roof surfaces may be caused by soot from chimneys, both wood-fired and oil-fired devices. Black or other colored stains may also appear on roof surfaces from nearby industrial activities. See Soot Staining.
Brown or red stains on roof surfaces are often caused by rust from wearing steel flashing or other on-roof metal products. See Rust Stains on Shingles.
Green roof stains on roof shingles, clay tiles, cement tiles, and asbestos cement roof shingles or newer fiber cement roof shingles are often caused by algae. For details see ALGAE STAINS ON ASPHALT ROOF SHINGLES. Moss on roofs is also often green and should be unmistakable in appearance. See ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES.
Moss on roofs and other building surfaces: see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES, and Green Stains on Stone. Green or other colored mosses are a bit easier to remove than lichens on roofing surfaces, but both can carry away mineral granules and damage the roof surface. Moss tends to hold more water and moisture on the roof surface. So in our opinion moss is more likely to damage a roof surface than lichens or algae. Also see ALGAE, FUNGUS, LICHENS, MOSS COMPARED.
Rust Stains on buildings - see Rust Staining - Red or Brown Rust Stains (on shingles)
Soot or Creosote black or brown stains on roof surfaces near or below chimneys - see SOOT STAINING - Black Soot Stains on Roof Shingles Around Chimneys and see Proximate cause roof shingle stains
Stains on stone or masonry surfaces - see STONE CLEANING METHODS for cause, cure, and prevention
White stains on roof surfaces may be from wash-down of pigments in paint on surfaces above the roof such as a gable end or dormer wall; white or less-black roof surfaces may also be found below copper or aluminum flashing whose salts run down the roof surface in wet weather, preventing algae or moss growth and leaving a white area on an otherwise stained roof surface. Our article at ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES includes a photograph of this condition on a wood shingle roof.
Questions & Answers regarding this article
Questions & answers about the best methods to clean stone surfaces
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Guides to identifying mosses, lichens, algae Graphic Guide Ontario Mosses (some of which appear widely dispersed by climate and geographic area, not just in Ontario) which offers a graphic guide to mosses. worldofmosses.com/ggom/index.html
Also see the sources listed at worldofmosses.com/ggom/ggomBibliography.html
Also see the Journal Folia Geobotanica, Springer, Netherlands ISSN1211-9520 (Print) 1874-9348 (Online) IssueVolume 11, Number 2 / June, 1976 DOI10.1007/BF02854759 Pages217-22
The Ecology of Algae, F.E. Round, Cambridge University Press, 1984 ISBN-10: 0521269067 ISBN-13: 978-0521269063 (Available at Amazon.com) After an introduction outlining the chemical and physical characteristics of the environment, the book goes on to look at the actual habitats in which algae occur. The communities of the individual habitats such as open water, sediments, rocky shores, coral reefs, hot springs, sea ice, soil, etc., are then discussed with special phenomena highlighted, for example rhythmic activity, nitrogen fixation and buoyancy. There are also chapters on seasonal cycles of algal growth, energy flow, geographical dispersion, palaeo-ecology and contribution to sediments. The importance of algae in symbiotic relationships and their considerable significance to animal grazers in aquatic food chains are also discussed. The final chapter deals with the relationships of algae to eutrophication and pollution of water. This is an important aspect, which can only be understood through an appreciation of algal ecology.
Lichens of North America, Irwin M. Brodo, Yale University Press, 2001, ISBN-10: 0300082495, # ISBN-13: 978-0300082494 (Available at Amazon.com)
Quoting from Library Journal: Lichens are a combination of a fungus and an alga but have a unique structure and appearance quite different from either. Existing worldwide and growing on a variety of surfaces, including rocks, soil, and trees, they may appear leafy, shrubby, mossy, crusty, or jellylike and are seen in a wide range of colors, from brilliant oranges, yellows, and reds to dull grays and browns. This huge new book, written by a world authority on lichens and emeritus research scientist at the Canadian Museum of Nature, Ottawa, provides information on about 1500 of the roughly 3600 recognized North American lichens. Part 1 introduces lichens in 14 clearly written chapters that discuss their biology, ecology, geography, environmental roles, and collection. Part 2, the heart of the book, is a guide that offers identification keys to groups, genera, and species and their descriptions, with accompanying photographs and North American distribution maps. The more than 900 truly beautiful, full-color photos were taken by the Sharnoffs, nature photographers whose work has been widely published in National Geographic, Smithsonian, and elsewhere. Of value to professionals and amateurs alike, this book is certain to be a classic reference for decades to come. Highly recommended for academic and research libraries and for public libraries where interest warrants; libraries needing only a brief yet informative introduction to lichens should consider William Purvis's inexpensive Lichens (Smithsonian Institution, 2000). William H. Wiese, Iowa State Univ. Lib., Ames
Cultural Heritage and Aerobiology, Methods and Measurement Techniques for Biodeterioration Monitoring, Paolo Mandrioli, Guilia Caneva, and Cristina Sabbioni, Eds., Kluwer Academic Publishers, 2003 ISBN 1-4020-1622-0 See our book review of this reference. The conservation of art objects relies on expert inspection, testing, and diagnosis of environmental contaminants and factors that affect the deterioration of artworks, such as mold, moisture, temperature, acid rain, and both indoor and outdoor air quality components. This text reviews these important art conservation concerns and describes methods for the inspection, testing, and monitoring of environmental conditions wherever artworks and other cultural artifacts are located.
Thanks to Patrick Walsh for discussing cleaning methods for gravestones & tombs May 2010. Mr. Walsh is experienced in the cleaning and restoration of antique gravestones and contacted us to discuss this topic.
"Assessing Cleaning and Water-Repellent Treatments for Historic Masonry buildings", Robert C. Mack, FAIA, Anne GrimmerU.S. National Park Service, web search 07/24/2010, original source: http://www.nps.gov/hps/tps/briefs/brief01.htm
Quoting from the document introduction: The purpose of this Brief is to provide information on the variety of cleaning methods and materials that are available for use on the exterior of historic masonry buildings, and to provide guidance in selecting the most appropriate method or combination of methods. The difference between water-repellent coatings and waterproof coatings is explained, and the purpose of each, the suitability of their application to historic masonry buildings, and the possible consequences of their inappropriate use are discussed. The Brief is intended to help develop sensitivity to the qualities of historic masonry that makes it so special, and to assist historic building owners and property managers in working cooperatively with architects, architectural conservators, and contractors. Although specifically intended for historic buildings, the information is applicable to all masonry buildings. This publication updates and expands Preservation Briefs 1: The Cleaning and Waterproof Coating of Masonry buildings. The Brief is not meant to be a cleaning manual or a guide for preparing specifications. Rather, it provides general information to raise awareness of the many factors involved in selecting cleaning and water-repellent treatments for historic masonry buildings.
Shingle Shield™ are zinc strips that are inserted under the shingle tabs of individual shingles to reduce moss, lichens, and algae growth on asphalt roofing - see shingleshield.com
StainhandleR are zinc strips that are inserted under the shingle tabs of individual shingles to reduce moss, lichens, and algae growth on asphalt roofing- see stainhandler.com
Zinc-Shield® - zincshield.com and Z-stop™ zinc roofing strips - z-stop.com, are roll-out zinc strips intended for installation near the ridge of a roof to reduce moss, lichens, and algae growth on roofs
04/09: thanks to William M. Norman, P.E., S.E., Keeler-Webb Associates, 486 Gradle Drive, Carmel, IN 46032 for opening discussion regarding the legitimacy of extractive bleeding as a term to apply to asphalt roofing material. Mr. Norman suggests that many (not all) black stains on asphalt roofing may be due to algal growth. We will report progress in this discussion as updates to this web article.
How to Recognize & Control Sooty Molds, USDA publication on the recognition and control of black sooty molds, including on buildings.
This publication is also available in printed form from the U.S. Government Printing Office, 1992 657-152 HT-69 1992. The original article was authored by Kenneth K.Kessler, Jr., Principal Plant Pathologist, U.S. Forest Service, in the Department of Agriculture of the United States. Copies are also available from North Central Distribution Center, Forest Products Laboratory, One Gifford Pinchot Dr., Madison WI 53705-2398.
"Microbes Eating Away at Pieces of History", Vina Venkataraman, The New York Times, 27 June 2008 p. F3.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Paint and Surface Coatings, Theory and Practice [purchase at Amazon.com], R. Lambourne & T.A. Strivens, Ed., Woodhead Publishing Ltd., William Andrew Publishing, 1999 ISBN 1-85573-348 X & 1-884207-73-1 [This is perhaps the leading reference on modern paints and coatings, but is a difficult text to obtain, and is a bit short on field investigation methods - DF]
Analysis of Modern Paints, Thomas J.S. Learner, Research in Conservation, 2004 ISBN 0-89236-779-2 [Chemistry of modern paints, overview of analytical methods, pyrolysis-gas chromatography signatures of basic modern paints and their constituents, Fourier transform infrared spectroscopy for paint analysis, direct temperature-resolved mass spectrometry, and analysis in practice - technical reference useful for forensic paint science, focused on art works -DF]
Seeing Through Paintings, Physical Examination in Art Historical Studies, Andrea Kirsh, Rustin S. Levenson, Materials in Fine Arts, 2000 ISBN 99-051835 [ forensic science, technical reference, focused on art works - DF]
Sealants, Durability of Building Sealants (RILEM Proceedings), J.C. Beech, A.T. Wolf, Spon Press; illustrated edition (1995), ISBN-10: 0419210709, ISBN-13: 978-0419210702 This book presents the papers given at the RILEM Seminar held at the Building Research Establishment, Garston, UK in October 1994. The book provides an opportunity for researchers to review up-to-date progress towards the achievement of the objectives of the standardisation of laboratory techniques of sealants in the variety of service conditions to which they are exposed.
Soiling and Cleaning of Building Facades (RILEM Report), L.G.W. Verhoef (Editor), Routledge; 1 edition (November 3, 1988), ISBN-10: 0412306700, USBN-13: 978-0412306709 The report of a comprehensive investigation by RILEM which examines all aspects of the cleaning of facades, subject to soiling by both biological and non-biological agencies. The contributors are international authorities working in this field giving essential advice to all those who need to know how to approach the problems connected with the soiling and cleaning of building facades.
Staining, Prevention of Premature Staining in New buildings, Phil Parnham, Taylor & Francis; 1996, ISBN-10: 0419171304, ISBN-13: 978-0419171300 The appearance of ugly staining early in a buildings life, ruins an otherwise pleasing appearance, tarnishes the image of the owners and gives rise to costly refurbishment works. In this book Phil Parnham raises a number of questions that should be considered whenever a new building is being designed or built. These are: * why has staining become so prominent; * what causes premature staining; which parts of new buildings are likely to be affected; * how can it be avoided? By using a number of highly illustrated case studies, the author answers these questions and ends by suggesting measures that should be taken by all design and construction professionals to prevent premature staining.
Paint Handbook: testing, selection, application, troubleshooting, surface preparation, etc., Guy E. Weismantel, Ed., McGraw Hill Book Company, 1981, ISBN-10: 0070690618, ISBN-13: 978-0070690615, [Excellent but a bit obsolete paint theory and practice, also a bit light on field investigation methods, out of print, available used-DF] How to select and apply the right paint or coating for any surface. The first major reference to help you choose the correct paint or other finish to do the job best on a particular surface exposed to a particular environment. Experts in the field give full advice on testing surface preparation, application, corrosion prevention, and troubleshooting. The handbook covers wood, metal, composites, and masonry, as well as marine applications and roof coatings. A ``must'' working tool for contractors, architects, engineers, specification writers, and paint dealers.
Paint and Surface Coatings, Theory and Practice, R. Lambourne & T.A. Strivens, Ed., Woodhead Publishing Ltd., William Andrew Publishing, 1999 ISBN 1-85573-348 X & 1-884207-73-1 [This is perhaps the leading reference on modern paints and coatings, but is a difficult text to obtain, and is a bit short on field investigation methods - DF] Provides a comprehensive reference source for all those in the paint industry, paint manufacturers and raw materials suppliers, undergraduate and postgraduate students, and industrial paint users. R. Lambourne was in the Research Department at ICI Paints Division and the Industrial Colloid Advisory Group, Birstol University, UK.
Understanding Ventilation, John Bower, The Healthy House Institute, ISBN 0-9637156-5-8, 1995 [General building science-DF - ** Particularly useful text. Mr. Bower has retired from the field but his book continues to be important]
"Moisture Control in buildings: Putting Building Science in Green Building," Alex Wilson, Environmental Building News, Vol. 12. No. 5. [Good tutorial, "Moisture 101" outlining the physics of moisture movement in buildings and a good but incomplete list of general suggestions for moisture control - inadequate attention given to exterior conditions such as roof and surface drainage defects which are among the most-common sources of building moisture and water entry.--DJF]
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