Why is my
Pool Deck turning green and black?
Frederick M. Hueston
What is that green and
black stuff growing on my pool deck? The majority of these unsightly spots are
the result of biological growth in the form of Algae, Molds, Lichens and Mosses as well as plants such as ivy and
grasses. The following guide will help you in identifying these biological
growths as well as removing and controlling them.
Biological Growth Types
Algae
Algae is commonly green in color but can also be
black, orange, red or yellow. It is easy to identify since it grows in mats,
films and patches on the surface of stone, brick and Concrete.
Algae is a single cell plant but lacks roots, leaves,
stems and vascular tissue. Most algae,
especially the green type needs moisture and sunlight to grow. However there
are species that will grow in low light but damp moist areas are usually
required.
Moss
The most common moss is green but can also be red.
Like algae it requires sunlight and moisture to grow but in addition needs a
mineral source often found in soils. Unlike algae it has root structure and a
very small leaf structure. It will often be growing in the grout between the
stone and masonry.
Mold
Mold is not a plant but a fungus. It does not require
sunlight but does require moisture and an organic food source. Mold is
generally black in color but can also be red, organe, brown or yellow. Mold
grows easily on many types of limestone since they contain organic matter to
feed the mold.
Lichens
Lichens comprise
a fungus living in a symbiotic relationship with an alga or cyanobacterium (or
both in some instances). They can be red, yellow, red, green, white or yellow.
They are identified by crusts or leaf like structures with defined borders,
growing away from the surface of the stone or masonry.
Ivy,
Grasses and Higher plants
These plants are easily
identified by there root system and there large leaf structure. They are often
green in color.
Removal of
Biological Growth
Regardless of the type
of biological growth removal requires the uses of biocide cleaning chemicals
such as peroxide, bleach and other biocides. The following is a basic cleaning
procedure that is recommended to remove these growths.
1.
Wear gloves
and protective clothing. A mask is recommended since some mold and algae spores
can emit spores which can be harmful to your respiratory system.
2.
Algae is
best removed when it is dry since the spores are more likely to become airborne
when wet. Allow the surface to dry or dry it with a fan. Once dry remove as
much as possible by scraping of scrubbing with a stiff broom or brush.
3.
A pressure
washer can be used to remove the remaining biological growth but there are some
precautions and recommendations as follows:
a.
Do not use
high pressure. Test the pressure in a non-conspicuous area to make sure you are
not damaging the stone or masonry.
b.
Use hot
water if possible. Hot water will also kill some of the biological growth as
well sanitize the surface.
c.
Use a wide
nozzle tip to minimize damage. Keep the tip of the wand at least 12 inches away
from the surface.
d.
4.
Bleach or
Vinegar can be used to clean suborn growth. Mix the bleach or vinegar. Use one cup
of bleach or vinegar with one gallon of water. test this mixture in a non-conspicuous
area to test for discoloration. Some stone and masonry types can lighten up
with bleach or vinegar.
5.
Apply the
bleach or Vinegar mixture on the deck and allow it to sit for 15-20 minutes. Do
not let it dry. If it dries, apply more of this mixture.
6.
After 15-20
minutes scrub the area with a nylon brush and rinse with plenty of clean water.
Be care of nearby plants since this mixture can kill landscaping plants and
grasses.
In lieu of bleach or
vinegar you can use many of the commercial cleaners that are available at most
home centers. Be sure to read the directions carefully.
Spot
Removal
If you have just a few
spots you can use 3% hydrogen peroxide. Simply spray the growth with the
peroxide, allow it to sit for several minutes and then rinse with water.
Prevention
To keep biological growth
at bay you should clean the deck on a regular bases. There are also sealers and
preventive biocides that are available which will hasten the growth. But you
best defense is to keep the deck clean.