cedar siding discoloration
Cedar enjoys a well deserved reputation as a
wood that takes and holds a range of finishes
for extended periods. Nevertheless, the normal
life of a finish will be shortened by
degradation and discoloration. The causes of
discoloration, though not in themselves a
failure of the finish, often requires remedial
treatment.
Dirt
Dirt is the most benign cause of
discoloration and not usually a problem. A
periodic cleaning with a mild detergent solution
will usually restore the surface finish.
Mildew
Mildew applies both to the fungus and to its
staining effects on both the finish and the
wood. Mildew is a common cause of discoloration
of paint, solid color stains and natural
finishes. Restaining does not solve a mildew
problem. When it is time to refinish, clean off
the mildew with a commercial mildew remover then
refinish with a coating that contains an
effective mildewcide.
Extractives Bleed
Extractives bleed that discolor the finish is
usually caused by moisture. To stop stains
caused by extractives bleed, moisture problems
must be eliminated. Mild staining is often
washed away by rain over a period of weeks. In
sheltered areas of the building where the stain
persists, it may become darker with age and more
difficult to remove. If washing with a mild
detergent solution does not work, a commercial
cleaner may help.
Iron Stains
Iron stains may appear in two forms: the
reddish brown discoloration caused by rust, and
blue black discoloration caused by the reaction
of iron from nails and other metal objects with
extractives from the cedar. To prevent these
stains, use only hot dipped galvanized, aluminum
or stainless steel nails when fastening cedar.
Water Stains
Water stains often occur in combination with
extractive bleed and mildew growth. These stains
can be difficult to remove. Scrubbing the wood
with an oxalic acid solution is sometimes
effective.
Caution: Handle oxalic acid solution with care
as it can be extremely harmful
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