yellow-cedar, and redwood. However, it is difficult to com-
pare the advantages and disadvantages of the two types of
cleaner (oxygen versus chlorine) because of the wide range
of active ingredient concentrations in the cleaners, additives
in the cleaners, and various wood substrates that have been
used for evaluating the cleaners. Some commercial products
contain household bleach. Commercial cleaners usually
have a surfactant or detergent to enhance the cleansing
action.
At the other extreme from the reported gentle bleaching ac-
tion of sodium percarbonate are those cleaners containing
sodium hydroxide. Sodium hydroxide is a strongly alkaline
chemical that pulps wood and is used in some paint strip-
pers. These cleaners may be necessary where mildew is
imbedded in a surface finish; however, they should be used
only as a last resort.
Manufacturers of some cleaners and brighteners report that
their products restore color to wood. Cleaning wood does
not add color. Removing mildew reveals the original color.
Brightening the wood may make it appear as if it has more
color. Weathered wood has a silvery gray appearance be-
cause weathering removes colored components from the
surface. If you want to restore color, stain the wood. Some
commercial cleaners pulp the wood surface and subsequent
power washing removes the pulped surface. In this case, the
color is “restored” because the surface of the wood was re-
moved. Sanding would give the same result.
Some brighteners contain oxalic acid. Oxalic acid removes
extractives bleed and iron stains, but it is not effective for
removing mildew.
Paint Strippers
Removing paint and other film-forming finishes from wood
is a time-consuming and often difficult process. Finish
removal is necessary if a finish has extensive cracking or
peeling (see Finish Failure or Discoloration). It may be nec-
essary to remove paint containing lead; however, if the paint
is still sound and it is not illegal to leave it on the structure,
paint over the lead-based paint to seal in the lead (see Lead-
Based Paint).
Methods described here can remove finishes from furniture;
however, companies that specialize in stripping furniture
usually immerse the furniture in a vat of paint stripper, then
clean and brighten the wood.
Mechanical and chemical are general types of stripping
methods. Consult product literature for additional informa-
tion on appropriate uses and safety precautions. Regardless
of the method used to strip paint, sand the wood prior to
applying new finish.
Note: Dust caused by mechanical stripping methods and
fumes given off by chemical strippers are usually toxic.
Use effective safety equipment, including a respirator,
even if the paint does not contain lead (see Lead-Based
Paint). Dust masks sold in hardware stores do not block
chemical fumes and are not very effective against dust.Mechanical Methods
Scraping, sanding, wet or dry sandblasting, spraying with
pressurized water (power washing), and using electrically
heated pads, hot air guns, and blowtorches are mechanical
methods for removing finishes.
Scraping is effective for removing loosely bonded paint
or paint that has already partially peeled from small areas
of the structure. If possible, sand weathered surfaces and
feather edges of paint still bonded to wood. Do not sand if
the old paint contains lead (see Lead-Based Paint).
If paint has partially debonded on large areas of a structure,
contractors usually remove the finish by power washing.
This methods work well for paint that is loosely bonded. If
paint is tightly bonded, complete removal can be difficult
without severely damaging wood. The pressure needed to
debond tightly bound paint from wood can easily cause deep
erosion of wood. If high pressure is necessary to remove
paint, the paint probably does not need to be removed prior
to refinishing. Power washing erodes less dense EW more
than dense LW, leaving behind ridges of LW, which are dif-
ficult to repaint. Power washing is less damaging to wood
than is wet or dry sandblasting, particularly if low pres-
sure is used. If more aggressive mechanical methods are
required, wet sandblasting can remove even tightly-bonded
paint. Dry sandblasting is not suitable for removing paint
from wood because it severely erodes wood along with the
paint and it tends to glaze the surface. Power washing and
wet and dry sandblasting are not suitable for paint con-
taining lead.
Power sanders and similar devices are available for com-
plete paint removal. Some devices are suitable for removing
paint that contains lead; they have attachments for contain-
ing the dust. Equipment that has a series of blades similar
to a power hand-planer is less likely to “gum up” with paint
than equipment that merely sands the surface. Planers and
sanders cannot be used unless the fasteners are countersunk.
Consult the manufacturers’ technical data sheets for detailed
information to determine the suitability of their equipment
for your needs and to meet government regulations on lead-
containing paint.
Paint can be softened using electrically heated pads, hot air
guns, or blow torches, then removed by scraping it from the
wood. Heated pads and hot air guns are slow methods and
cause little damage to the wood. Blowtorches have beenChapter 16 Finishing of Wood