Bleaching Wood

bleaching 5F00 lead Bleaching Wood

Bleaching Wood

Subtract color
to add life

By Michael Dresdner

There are four types of bleach that
woodworkers commonly use:
chlorine, two-part wood bleach, oxalic
acid and peroxide. Two-part bleach
changes the actual color of wood and
the other three remove stains. Read on
to find out what each one does and
how to use them safely.

 

Chlorine bleach

Common household laundry bleach
(sodium hypochlorite) will kill mildew
on your deck and outdoor furniture,
and will remove dye-based stain, but
not pigment-based stain, from wood.
Chlorine bleach can irritate skin and
mucous membranes, so wear gloves
and goggles.

Deck cleaner. To remove mildew
from your deck or exterior furniture,
first hose off the wood to remove any
loose debris. Mix about a quart of
chlorine bleach (Clorox, Purex, etc.) to
each gallon of water. Use a syntheticbristle
brush and scrub the surface
with the bleach mixture. Be sure to
wear goggles—it’s easy to splash.
Reapply the bleach if necessary in order to keep the surface wet for about
15 minutes. Then, brush off the surface
again and hose it down thoroughly
with water. Keep the runoff away
from plants, pets and other wildlife.

Fortunately, deck stains are formulated
with pigments, so they are not
affected by the bleach. Let the wood
dry completely if you plan to re-stain.
If you live in an area where mildew is
a problem, choose a deck stain that
contains a mildewcide, or add some
yourself. Most home centers and paint
stores sell them.

Dye remover. Chlorine bleach will
remove most dye-based stains from
raw wood but will not lighten the
wood itself. This is handy to know if
you finish your project with a dye,
and then decide you want to “erase” it
and start over. Chlorine bleach will
also remove old dye that you might
encounter during a refinishing project.

Use a synthetic-bristle brush or a
clean rag to apply the bleach full
strength. It should remove the color
by the time it dries, but for stubborn
stains, repeat the process. If you are
removing the stain from an old piece
of furniture that you are refinishing,
make sure all the finish is off the surface
and lightly scuff-sand it first.
Bleach will not go through a finish.

As bleach dries, it breaks down to
salt and water. Once the water evaporates,
you’ll have salt residue on the
wood. Brush it off before you finish
the wood.

 

Two-part (A/B) wood bleach

Wood bleach actually lightens the
color of wood. It can also de-color
many pigments and dyes.

A package of wood bleach contains
two bottles, usually labeled “A” and
“B.” One contains lye (sodium
hydroxide) and the other peroxide
(hydrogen peroxide). The bleaching
action occurs when the two chemicals
come together in contact with wood.

Instructions for use vary from brand
to brand. Some say to put part A on
first, then apply B before A dries.
Others suggest mixing the two just
before application. The object is to get
both chemicals and the wood all in
the same place at the same time. Read
the directions.

Use a synthetic-bristle brush or a
clean rag to apply the bleach. When
the lye goes on first, it initially darkens
the wood. Once the peroxide goes
on it is likely to foam as it reacts
with the wood and lye. Let the
wood dry completely, usually
overnight, then sponge off all
residue with plenty of clean water.

 

Oxalic acid

Iron, in the form of nails, hardware,
or even bits of steel wool, often leaves
a blackish stain on woods high in tannin,
like oak. A wash of oxalic solution
removes these stains as well as the
grayed color of oxidized wood.

Oxalic acid is sold in most hardware
stores and home centers as a dry,
white crystalline powder. The crystals
are toxic and irritating to mucous
membranes, so wear goggles and a
dust mask when handling the dry
powder. In a glass or plastic container,
dissolve an ounce of oxalic acid into a
pint of warm water.

Make certain that you have
removed all the offending metal
before you bleach the wood.
Sometimes stains are caused by broken-
off nails or bits of fencing that are
hidden in the wood. Wet the surface
with the oxalic acid mixture and let it
dry. Repeat if the stain is not completely
gone. Once dry, sponge the wood with plenty of clean water to
remove the crystalline residue. Any
oxalic acid residue left in the wood
will make irritating dust when you
sand, so wear a dust mask and eye
protection.

 

Peroxide

Maple is prone to a particular type of
blue stain that is caused by mold during
the drying process. A strong, 35-
percent peroxide solution, like the
“B” portion of wood bleach, can
usually remove the stain.

Concentrated peroxide is
very caustic, so wear goggles,
gloves, and a
waterproof apron.

You can buy 35-
percent peroxide
solution from a chemical
supply company, or borrow
it from your box of two-part
wood bleach. Flood it onto the maple
with a foam brush and let it dry completely.
There is no need to wash it
down, since peroxide (H2O2) neutralizes
itself to water and oxygen. In
extreme cases, when the peroxide
alone won’t do the trick, two-part
wood bleach will.

Click any image to view a larger version.

bleaching 5F00 wardrobe Bleaching Wood

Use bleach like stain. Two-part wood
bleach turns red oak bone-white,
without obscuring the grain the way
a pickling stain would. The top coat
is water-based polyurethane.

bleaching 5F00 chlorine 2D00 bleach Bleaching Wood

Chlorine bleach, full strength, easily removes most dye-based stain (right) but will not bleach raw wood white (center), nor will it remove pigment-based stain (left).

bleaching 5F00 two 2D00 part 2D00 bleach Bleaching Wood

Two-part wood bleach takes the color out of most dark
woods and blends maple heartwood color with its sapwood.

bleaching 5F00 safely Bleaching Wood

Apply A/B bleach safely. Wear long neoprene gloves, with
ends cuffed to catch drips, a
waterproof apron, and goggles.
Brush carefully. A/B bleach is
extremely caustic and will quickly
burn your skin and eyes.

bleaching 5F00 oxalic 2D00 acid Bleaching Wood

Oxalic acid dissolved in water
removes black iron stains
like magic from tannin-rich
wood like oak.

This story originally appeared in American Woodworker April 1999, issue #72.


AW72 Apr99 Cover Bleaching Wood


April 1999, issue #72


Purchase this back issue.

 

 Bleaching Wood

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