SAFE, NO-PRESSURE CLEANING
removed the striping from the Hilton
by eliminating the growth of the
bacteria that cause it.
Stud or structure striping is a pat- tern of bacterial growth seen on building exteriors. These dark
stains are generally visible in shaded
areas – such as the north sides of structures – and occur primarily in areas
with consistent moisture and humidity
levels, most often in moderate, marine
What Causes the
The primary catalyst for structure
striping on building exteriors is the cyanobacteria Gloeocapsa magma (GM).
Moisture is required for the dark bacteria to grow and become apparent. The
stripe pattern occurs due to transfer of
heat from structural components, including studs, rafters, headers and plates.
With the transfer of heat from internal structural members to the building
surface, areas in direct contact with the
heated structural framing dry quicker
than other areas, such as open or insulated bays.
In areas not heated by underlying
framing, bacteria are able to flourish.
Over time this results in a pattern that
clearly shows the framework of structural components just below the building’s exterior surface.
Roofs Are Affected by
This striping phenomenon is not
only found on walls, but on roofing as
well – particularly composition asphalt
roofs, with rafters serving to transfer
the heat. However, wood and tile roofs
don't typically exhibit bacterial striping.
The reason these materials are relatively
unaffected by bacterial growth is due
to their thicker dimension and insulative
properties. Tile roofs, when correctly
installed and insulated, create a thermal
barrier that doesn’t come into contact
with the heat transferred by structural
While darker colors downplay the pattern effect, lighter colors make striping
more pronounced. And, as the bacteria
are allowed to proliferate and darken
with time, areas subject to GM bacterial
growth become much more concentrated
and visible in areas with nonexistent or
While virtually all areas in the U.S. are
subject to the growth of the dark GM
bacteria, the striping pattern is generally only seen in moderate climates.
This is because structures built in colder
climates have much higher standards
for insulation, which limit the release of
internal heat to the exterior. Solid building materials, such as brick and mortar,
also disperse heat equally and show no
effects of structure striping.
Smaller buildings with many windows,
doors and comparatively detailed exte-
riors tend to obscure the pattern effect
and can make the pattern hard to see.
On the other hand, commercial buildings with large monotone, single-color
surfaces are much more prone to the
effects of structure striping. The pattern
is clearly visible and results from both
metal and wood framing.
The Most Effective Way
to Remove Structure
The safest, most effective way to
remove the bacteria that causes struc-
ture striping is using a non-pressure,
chemical cleaning process.
There are three distinct reasons for this:
1) Chemical or “soft wash” cleaning
eliminates bacteria as the source of the
staining. Because the bacteria itself is
being remediated, it takes years in most
cases for regrowth to occur, to the point
where it may become visible again.
2) The chemical solution to remove
structure striping is a safe, yet powerful
oxidizer. This results in the immediate
and generally complete removal of any
3) Perhaps most importantly is the
efficacy of soft (safe) washing. Contract
cleaners have traditionally used high
pressure for exterior cleaning. As mentioned earlier, structure striping typically
occurs in moderate climates. The most
common exterior building finishes and
materials used in these climates are
relatively delicate coatings, applied over
gypsum and acoustic board.
High pressure has proven to be an
ineffective means to remove bacterial
structure striping in most cases. The use
of high pressure has caused irreversible
damage to many costly building exteri-
ors. This isn't just due to human error:
The use of high pressure is simply the
wrong approach to cleaning many mod-
ern building exteriors.
Eric Schnaible is an exterior restoration
specialist with Pacific Exterior in Santa
What is Bacterial Structure Striping?
HOW TO REMOVE THE BACTERIAL GROWTH FROM YOUR BUILDING
THIS HILTON HOTEL was power-
washed just a week before this photo
was taken. Bacterial structure striping
is already visible.