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EXTERIORS of buildings
ADHESIVES, EXTERIOR CONSTRUCTION
AGE of a BUILDING - how to determine
ALGAE, FUNGUS, LICHENS, MOSS
ANIMAL ENTRY POINTS in buildings
ARCHITECTURE & BUILDING COMPONENT ID
BASEMENT WALKOUTS & COVERS
BRICK VENEER WALL Loose, Bulged
BRICK WALL DRAINAGE WEEP HOLES
BOOKSTORE - EXTERIORS
CAULKS & SEALANTS, EXTERIOR
CHIMNEY INSPECTION DIAGNOSIS REPAIR
DECK & PORCH CONSTRUCTION
DECK FINISHES COATINGS PRESERVATIVES
DRYWELLS, FRENCH DRAINS for FLAT SITES
EIFS & STUCCO EXTERIORS
EXTERIOR WALL SIDING TRIM & FINISHES
EXTRACTIVE BLEEDING STAINS
FLASHING ROOF-WALL SNAFU
GALVANIC SCALE & METAL CORROSION
GLUES ADHESIVES, EXTERIOR CONSTRUCTION
GRADING, DRAINAGE & SITE WORK
GUTTERS & DOWNSPOUTS
HOUSE PARTS, DEFINITIONS
HOUSEWRAP / SHEATHING WRAP
ROOF ICE DAM LEAKS
INSECT INFESTATION / DAMAGE
LEAD POISONING HAZARDS GUIDE
LOG HOME GUIDE
PAINT & STAIN GUIDE, EXTERIOR
PAINT FALURE, DIAGNOSIS, CURE, PREVENTION
PORCHES & Sunrooms
PORCH CONSTRUCTION & SCREENING
RAILINGS, DECK & PORCH
RETAINING WALL DESIGNS, TYPES, DAMAGE
ROOF CLEANING RECOMMENDATIONS
ROT RESISTANT LUMBER
SHEATHING, Gypsum board
Sheathing Celotex Homasote & Other
SHEATHING, FOIL FACED - VENTS
SIDING TYPES, INSTALLATION, DEFECTS
SINKHOLES, WARNING SIGNS
STAIN DIAGNOSIS on BUILDING EXTERIORS
STAIRS, RAILINGS, LANDINGS, RAMPS
STONE CLEANING METHODS
STONE VENEER WALLS
STUCCO WALL METHODS & INSTALLATION
SURFACE GRADING, SITE DRAINAGE
Thermal Expansion Cracking of Brick
TREES & SHRUBS, TRIM OFF BUILDING
TRIM, EXTERIOR CHOICES, INSTALLATION
VINYL Siding or Window PLASTIC ODORS
WATER BARRIERS, EXTERIOR BUILDING
WATER ENTRY in buildings
WINDOWS & DOORS
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 include links to references & researh useful in the identification & control of algae, moss, lichens, and mold.
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Methods for Cleaning Organic Growth (Algae, Fungus, Lichens, Moss) from Stone, Brick, or Concrete Surfaces
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:
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.
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:
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 Surfaces1 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.
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 buildng 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. orry, 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 STAIN DIAGNOSIS on STONE 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
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