bleach to five parts water should be adequate. In no case
should a mixture stronger than one part bleach to three
parts water be necessary. Add a little powdered detergent to
help remove the dirt. Do not use liquid detergent because
it may contain ingredients that react with bleach to give
toxic fumes. Gently scrub the surface with a bristle brush
or sponge and rinse thoroughly. Rinse using a garden hose,
keeping the water stream pointed down to avoid flooding
the back side of siding with water. If using a power-washer,
keep the pressure low to avoid damaging the wood and, as
with the garden hose, keep the water stream pointed down.
Refinish the cleaned surface as soon as it has dried using a
finish containing a mildewcide.Household bleach mildew remover- 1 part (5%) sodium hypochlorite (household bleach)
(1 gallon) - 3 to 5 parts warm water (3–5 gallons)
- A little powdered household detergent (1/2 cup)
Warning: Do not mix bleach with ammonia or with any
detergents or cleansers that contain ammonia. Mixed
together, bleach and ammonia form a toxic combination,
similar to mustard gas. Many household cleaners contain
ammonia, so be careful in selecting the type of cleaner to
mix with bleach. Avoid splashing the cleaning solution on
yourself or plants.Loss of Gloss and Fading
Loss of gloss and fading typically occurred with traditional
oil-alkyd finishes. Although modern acrylic-based latex
finishes do not give the high gloss of an oil-alkyd, they
maintain gloss much longer. Some pigments fade more than
others; check with the paint manufacturer to ensure that the
colors will last. White is always a safe choice. The paint
and solid-color service-life estimates given in Tables 16–4
and 16–5 do not take into account loss of gloss and fading.
Many dark-colored finishes will fade to give unacceptable
performance long before the finish fails.Water-Soluble Extractives
In many hardwoods and softwoods, the heartwood contains
water-soluble extractives. (Sapwood does not contain water-
soluble extractives.) Western redcedar and redwood are
two common softwoods that contain highly colored water-
soluble extractives; extractives give these species their at-
tractive color, but they can also discolor paint. When wood
gets wet, water dissolves some extractives; then as the wood
dries, water carries water-soluble extractives to the surface.
The water evaporates leaving extractives behind as a reddish
brown stain. Discoloration shows in two ways: diffused and
run-down extractives bleed.
Diffused extractives bleed is caused by (1) water from rain
and dew that penetrates a porous or thin paint coating, (2)
water that penetrates joints in the siding, railings, or trim,and (3) absorption of water vapor in high humidity areas
such as bathrooms, swimming pools, and greenhouses
(Fig. 16–25).
Good painting practices prevent diffused extractives bleed.
Use an oil-alkyd stain-blocking primer or a latex primer
formulated for use over woods like redwood. Do not use
porous paints such as flat alkyds or latexes directly over
extractive-rich woods. If the wood is already painted and
is discolored by extractives, clean the surface and apply a
stain-blocking primer. Allow sufficient time for the primer
to cure so that it blocks the extractives, and then apply top-
coat.
Run-down extractives bleed is caused by (1) water draining
behind siding from roof leaks, faulty gutters, or ice dams,
(2) condensation of water vapor, originating inside the struc-
ture, on the back side of siding, and (3) wind-blown water
that wets the back side of siding. The water on the back side
of the siding dissolves extractives and runs off of the backChapter 16 Finishing of Wood
Figure 16–25. High moisture content of wood can
cause diffuse extractives bleed, particularly if a stain-
blocking primer is not used.Figure 16–26. Water-soluble extractive discoloration
can result from water wetting the back of the siding
and then running down the front of the board.