Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
EXTERIORS of buildings
ADHESIVES, EXTERIOR CONSTRUCTION
AGE of a BUILDING - how to determine
ALGAE, FUNGUS, LICHENS, MOSS
ARCHITECTURE & BUILDING COMPONENT ID
ATTIC CONDENSATION CAUSE & CURE
BARK SIDE UP on DECKS & STEPS
BEST CONSTRUCTION PRACTICES GUIDE
BRICK VENEER WALL Loose, Bulged
BRICK WALL DRAINAGE WEEP HOLES
BOOKSTORE - EXTERIORS
CAULK GUN TYPES, CHOICES
CAULKS & SEALANTS, EXTERIOR
CHIMNEY INSPECTION DIAGNOSIS REPAIR
DECK & PORCH CONSTRUCTION
DEFINITIONS of ENGINEERED WOOD OSB LVL etc
EIFS & STUCCO EXTERIORS
ENGINEERED WOOD Products
EXTERIOR WALL SIDING TRIM & FINISHES
FLASHING MEMBRANES PEEL & STICK
FLASHING ROOF WALL DETAILS
FLASHING SIDING DETAILS
FLASHING WALL DETAILS
FLASHING WINDOW DETAILS
FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
GALVANIC SCALE & METAL CORROSION
GLUES ADHESIVES, EXTERIOR CONSTRUCTION
GUTTERS & DOWNSPOUTS
HOUSE PARTS, DEFINITIONS
HOUSEWRAP / SHEATHING WRAP
ICE DAM PREVENTION
INSECT INFESTATION / DAMAGE
LEAD POISONING HAZARDS GUIDE
LEED GREEN BUILDING CERTIFICATION
LOG HOME GUIDE
MOISTURE CONTROL in BUILDINGS
ODORS GASES SMELLS, DIAGNOSIS & CURE
PAINT & STAIN GUIDE, EXTERIOR
PORCHES & Sunrooms
PORCH CONSTRUCTION & SCREENING
RETAINING WALL DESIGNS, TYPES, DAMAGE
ROT RESISTANT LUMBER
ROT, TIMBER ASSESSMENT
SHEATHING, Gypsum board
SHEATHING, FOIL FACED - VENTS
SIDING TYPES, INSTALLATION, DEFECTS
SINKHOLES, WARNING SIGNS
STAINS on & in BUILDINGS, CAUSES & CURES
STAIN DIAGNOSIS on BUILDING EXTERIORS
STAIN DIAGNOSIS on STONE
STAIRS, RAILINGS, LANDINGS, RAMPS
STONE CLEANING METHODS
STRESS SKIN INSULATED PANELS
STRUCTURAL DAMAGE PROBING
STUCCO WALL METHODS & INSTALLATION
SURFACE GRADING, SITE DRAINAGE
TEST KITS for DUST, MOLD, PARTICLE TESTS
Thermal Expansion Cracking of Brick
THERMAL EXPANSION of MATERIALS
TRIM, EXTERIOR CHOICES, INSTALLATION
TRIM, INTERIOR INSTALLATION
VAPOR BARRIERS & CONDENSATION in BUILDINGS
VENTILATION in BUILDINGS
VINYL CHLORIDE HEALTH INFO
VINYL Siding or Window PLASTIC ODORS
VOCs VOLATILE ORGANIC COMPOUNDS
WATER BARRIERS, EXTERIOR BUILDING
WATER ENTRY in buildings
WINDOWS & DOORS
Vinyl siding stain diagnosis: this article discusses common causes of stains or discoloration found on vinyl building siding. Distinguishing the type of stain found on siding is useful in deciding on the cause and thus the cure or prevention of staining. Dirt from rain splash-up, algae, lichens, mold, moss, or even smoke or chemical stains have different causes and different preventative measures. Shadows, moisture variations that collect or don't collect dust on siding, even roof leaks or air leaks through building walls can often be diagnosed by a close look at wall stain patterns discussed here.
Green links show where you are. © Copyright 2014 InspectApedia.com, All Rights Reserved.
As we complain throughout InspectAPedia.com, mildew, a proper subset of the larger family of molds or fungi, does not grow on buildings - mildew grows on living plants.
But people often refer to mold growth on surfaces as "mildew" and so product manufacturers selling cleaners intended to remove mold will understandably call them "mildew removers". It's mold - if you care.
The photo at above left shows green algae on vinyl siding. Algae may also look black or brown, as may some molds.
Small gray or darker round spots on siding that are about 1/16" in individual diameter, particularly if the spots are slightly raised may be artillery fungus - a mold spore.
Algae on building walls: Algae is often confused with mold. In our photo at above left shows a common condition that is found on many types of building siding: green (or brown or black) algae growth. Algae is found on siding that is shaded and stays damp.
While algae stains on exterior walls are principally a cosmetic concern and can be cleaned using scrubbing, mild soaps, or more aggressive TSP-substitute cleaners or detergents, there may remain a hidden problem: any building wall that stays damp and shaded may be at higher risk for hidden insect or rot damage.
If there is an accessible crawl space or basement below a wall that looks like the one in our photo, that's a good place to look for signs of building leaks, rot, or insect damage.
In our photo just above we think these black specs may be a fungal growth. A pen cap is included in the photo for scale. Artillery fungus can produce black specs on a building wall, trim, or other outdoor surfaces. Similar black specs may be found on exterior siding where the attachment points of vines have adhered to the surface.
In our photo at above left you are looking at dirt and dust on building siding; that vertical light colored streak shows where water has washed away some of the surface debris. "Is that a problem?" is a common question. Probably not. Look above the water streak for a drain opening that is permitting condensate to drain off from the back side of the building siding ouit onto the siding exterior surface. Such markings may be normal.
But extensive water streaks down exterior siding may indeed indicate a wall or roof leak that needs to be tracked down and repaired. Our photo at above right shows that water has been leaking out of this vinyl-clad wall (in winter in a northern climate); further investigation and repair are needed, and there is a risk of hidden rot damage, insect damage, or mold contamination in the wall cavity; I'd also worry that water leaking into the wall cavity may have wet insulation.
Advice for Dealing with Algae or Mold on Outside Walls
A microscopy lab examination of a sample from this surface would be needed to know for sure. But testing is probably not justified.
Where there are apparent "growth" substances on a building exterior wall we offer the following added advice:
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
Question: Chalking surface of older vinyl siding - is this normal
I am wondering why when I rub my fingers across our siding I come away with my fingers being white. Is this a normal vinyl siding thing or does it mean it has been previously painted or what? I want to clean the siding but would like to know what the white stuff is first. - Anon 8/18/2011
Watch out: any older oxidized plastic may have increased in brittleness and be more vulnerable to mechanical damage.
Question: I found carpenter ants behind my siding - how do I fix the problem
after i took down insulation i found a lot of carpenter ants ,killed them . investigated more around the house noticed in the garage that there were more took down sheet rock water damaged. j channel cut and holes with wood showing .how do i fix this? - Dale 7/21/12
Dale you're going to need to follow the water backwards until you've found the leak or water entry point; fix that, and restore the siding; You'll need the "siding hook" siding replacement tool we describe if you're working from the bottom of the wall up.
Questions & answers or comments about Vinyl Siding on Buildings, Installation, Inspection Methods, Defects, Diagnosis & Repair.
Try the search box just below or if you prefer, post a question or a comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.