from the bright work is one of those contentious issues the wooden boat
Unsightly marks are caused by
mold, weathering or by
chemical reaction between metals and tannic acid in the wood.
Sanding is the best way to get
down to good wood.
However, sometimes if the
stains are too deep bleaching is
the only solution, unless you are prepared to stain the whole area
blend in the stains.
Wood Stain Removal
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Bleaching wood is
accomplished by using highly reactive
chemicals that break down the color in the wood.
These bleaches are poisonous and
caustic so, wear the
appropriate protective gloves, safety glasses and if mixing dry bleach
wear a dust mask.
Knowing the cause of the stain will
help you to select the
correct bleach but in most cases you'll need to experiment on a trial
You may find that a particular wood
react to a bleach, so you may have to try a different one.
And not all woods react well, oak
reacts well, whereas
chestnut won’t, so always do a check on your wood stains first.
There are three types of bleaches
used on wood, peroxide
or “two-part’ bleaches, chlorine bleach and oxalic acid.
Oxalic acid is the one to try first,
then if that
doesn’t work chlorine and as a last resort one of the two part
Before trying any bleach it’s always
worth trying to
sand the offending wood stain clean, sometimes it is surprising how
material must actually be removed.
Oxalic acid is particularly
removing wood stains
formed when iron and moisture come into contact with tannic acid in the
Woods such as oak and mahogany
naturally contain a high
amount of tannic acid.
Oxalic acid can be used to remove
without affecting the natural color of the wood.
It can also be used to lighten the
weathering, which is why it is found in most 'deck washes'.
Oxalic acid comes in the form of
crystals, which are mixed
with warm water and then applied with a brush or sponge.
Once the stains are gone you need to
neutralize the acid so it will not react with your wood finish.
Mix up two tablespoons of borax in a quart
of hot water.
Or use a solution made from one-quart water
with two heaping tablespoons of bicarbonate
Saturate a rag with the solution, wipe the wood
clean, rinse it again with clean water, and allow it to dry thoroughly.
Or use the solution
by the instructions that come along with the bleach.
Chlorine is a strong oxidizer that is more
appropriate for removing or
lightening dye stains.
A weak chlorine based bleach will
probably require too
many applications to be effective.
A strong solution can be made from
the stuff used in swimming pool bleach.
It is inexpensive and can be
purchased from a pool
These are the two-part bleaches.
parts are usually sodium
hydroxide and strong hydrogen peroxide.
When they are mixed together they
become a strong
This is very effective at removing
the natural color from
These two part solutions need to be
washed off with a
'neutralizer' such as plain water, water mixed with white vinegar or
solution recommended in the instructions that come along with the
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your wood down to a reasonable finish before bleaching, so the
do its work properly.
Once the wood stains have been
bleached you should only
sand it lightly with a fine grit to remove the grain that has been
the bleach and the neutralizer.
Use some cheap disposable brushes to
apply the bleach as
they will not be fit for any other use afterwards.
If using oxalic acid, mix a solution
of dry crystals in
hot water and apply to the entire surface, not just the stain.
You may need several applications
allowing it to dry
overnight drying in between coats.
Once you are satisfied with the
results and the area is
perfectly dry any residual oxalic acid must be washed off before
using a two part peroxide
bleach, wash the area down with mineral spirits after sanding and allow
dry well for a couple days.
Then using a paint brush, apply a
generous even coat of
the first part of the bleach.
sure that there are no
drips or missed spots, then wipe off any excess with a rag.
Allow this to stand for about 5 or 10
Then apply part two, using a separate
Make sure that you cover all the
areas treated with the
Again wipe off any excess with a
clean rag and allow it to
sit for a few hours before washing down with the neutralizer.
Allow to dry at least overnight
before attempting to
finish or if necessary, applying a second application.
If you end up with a few streaks or
an uneven tone you may
have to rectify this with a final treatment of oxalic acid.