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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
This article describes and provide photographs and microscopic photographs of algae, moss, lichens, or fungal growth that occurs on buildings and in nature. We include links to references useful in the identification of algae, moss, lichens, and mold. Our photo at page top shows moss on an asphalt shingle roof.
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This article series tells readers how to identify, evaluate, remove or prevent stains on building surfaces.
Black stains due to algae: Algae often appears on organic and even inorganic surfaces of buildings and in nature such as on the asphalt roof shingles in this photo.
Black algae stains can also look a lot like extractive bleeding shown in this separate article on "EXTRACTIVE BLEEDING on SHINGLES" which can appear on asphalt roof shingles.
While algae is the most common source of black or green roof stains on shingles, when the staining or bleeding appears to run down the roof from individual small points or "spots" this may be something other than a fungal growth or soot: it may b e extractive bleeding or "bleed through" on shingles. (See ALGAE STAINS ON ASPHALT ROOF SHINGLES and also STAINS on ROOF SHINGLES for a more detailed discussion of bleed through or extractive bleeding as well as black algae stains on roof shingles.)
The presence of algae on the roof is an indicator that this roof area is in a shaded spot where you may want to be alert for development of moss or other roof problems, but the level of damage from algae is probably low, even less than that caused by lichens.
Avoid any aggressive cleaning methods that might damage the roof surface.
Green or black stains due to algae: green stains also appear on buildings including on shingles, siding, and even on masonry walls, sidewalks, planters, and retaining walls: stone, concrete block, and concrete.
If you see flat green stain on a building exterior and that is not producing any plant-like raised growth it is likely to be an algae.
Watch out: on walks and decks algae makes for a dangerously slippery surface when it is wet. Details are at Slippery Stairs, Walks.
Also see STONE CLEANING METHODS for details about cleaning and prevention of algae or moss growth on outdoor and other surfaces.
Algae under the microscope has a distinctive appearance that easily distinguishes it from moss, lichens, and mold, as we show here.
This microphotograph of algae was made in our lab while examining a sample sent to us from our friend and mold lab expert Sue Flappan.
The original algae sample was collected from a concrete sidewalk using simple adhesive tape.
Lichens, one of the most hardy growth organisms found in nature, can grow in harsh conditions. Lichens is often found growing on roof shingles, especially asphalt and wood shingles as we show here.
Our photographs (above) show lichens growing on an asphalt roof shingle in situ (above left). In the photo where our pen is inserted for scale (above right) we had "picked" the spot of lichens gently and flipped it over.
Our pen points to the hole left in the asphalt shingle as the lichens had such a good grip on the mineral granules that when removing the lichens it brought some of the roof protective coating along with itself. If you click to enlarge the photo at above right you'll see the actual mineral granules from the shingle adhered in the "roots" of the lichens.
See LICHENS on ROOFS for details about the causes, effects, and prevention of lichens growth on roofing surfaces.
Also see LICHENS on STONE SURFACES.
Moss growing on any roof surface will be more severe on roof sections that area shaded and exposed to periodically damp cool weather conditions.
The presence or absence of much sunlight on a roof surface is often a determining factor in the amount of moss or lichens growth (more sun, less moss and lichens.
Moss and lichens are more than a cosmetic issue on many kinds of roofing materials - asphalt shingles, roll roofing, wood shingle roofs, wood shake roofs. By holding moisture against the roof surface lichens but more so moss speed the wear of the asphalt shingle surface in freezing climates by increasing frost damage to the mineral granule coating on the shingles.
What Moss Looks Like Under the Microscope - photos
It's easy to see the plant-like structure of moss fragments, as our photograph (left) demonstrates.
This moss sample was collected from a basement wall: we suspect that the damp conditions that produced this moss growth on the building wall also increased the risk of a mold problem in the same structure.
For an identification guide to mosses we include some resources below at Reviewers.
For an extensive catalog of methods for preventing algae, moss, or lichens growth on roofs see How to Prevent Moss, Lichens & Algae Growth on Roofs.
See Black Stain Removal & Prevention for advice on diagnosing, cleaning, and preventing algae stains on roofing.
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.
Our photo (left) shows algae formation in a fresh water lake near a failed septic drainfield.
See SEPTIC DRAINFIELD FAILURE DIAGNOSIS and SEPTIC FAILURE SPOTS where we describe where effluent typically shows up when the disposal field is failing, including causing algae blooms in nearby waterways.
A complete building exterior stain diagnosis list is given at STAIN DIAGNOSIS on BUILDING EXTERIORS.
See BLACK STAIN REMOVAL & PREVENTION for advice on diagnosing, cleaning, and preventing algae stains on roofing.
See STONE CLEANING METHODS for a discussion of the mechanical, chemical, lighting, heat and other methods used to remove algae, lichens, moss, and fungi from stone, masonry, roadways, and other exterior surfaces.
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