Once rot gets a toehold in wood it is
difficult to cure completely -- it is like a cancer. Digging out the
rotted wood will still leave spores and water in the sound wood. After
you fill in the cavity with something like epoxy, the rot continues to
flourish underneath. Products promoted to make rotted wood sound and
stop rot penetrate only until they meet water, with which they do not
mix. Under the solid repair rotting goes on. With one exception (more
later), the commercial products sold to treat dry wood to prevent rot
are completely ineffective against established rot in wet wood because
they are dissolved in petroleum solvents and oil and water do not
mix.
There are two commonly available inexpensive
materials that will kill rot in wood and prevent its recurrence. First,
there are borates (borax-boric acid mixtures) which have an established
record in preventing rot in new wood and in killing rot organisms and
wood-destroying insects in infested wood. Second, there is ethylene
glycol, most readily available as auto antifreeze-coolant. Glycol is
toxic to the whole spectrum of organisms from staphylococcus bacteria to
mammals. All of the published material on its effectiveness against
wood-destroying fungi and insects that I am aware of is the result of my
investigations over the past 15 years.
Both borate solutions and glycol penetrate dry and
wet wood well because they are water-soluble; in fact, penetration by
glycol is especially helped by its extreme hygroscopicity -- its strong
attraction for water. For both, the fact that they are water-soluble
means they are not permanent solutions to rot in wood that is
continually exposed to water-below the waterline and in ground-where
they will eventually be extracted-dissolved out.
I first was interested in glycol as a
wood-stabilizing agent, where it is in many ways superior to
polyethylene glycol (PEG), and it was during this work that I realized
the useful effect of glycol on organisms, though I was pretty dense in
interpreting the first experiment.
The ladies immerse the stems of greenery such as
magnolia branches in glycerin to keep them green. Glycol is very similar
to glycerin in all its physical properties and much cheaper, so I stuck
a magnolia branch in antifreeze. The next day it was brown. After the
third attempt I tumbled to the fact that the glycol was killing the
greenery. This was the reason that glycol never replaced glycerin in
applications such as a humectant for tobacco and an ingredient of
cosmetics and pharmaceutical ointments, though it had all the desirable
physical properties.
I had two 2" thick slabs of a 14" diameter hickory
tree that had just been cut. I treated one with antifreeze and left one
untreated. I was looking at wood stabilization, not rot prevention.
After about six months stored inside my shop the untreated control was
not only cracked apart, but it was sporting a great fungal growth, while
the treated slab was clean.
The local history museum wanted to exhibit two
"turpentine trees", longleaf pines that had many years ago been gashed
to harvest the sap that made everything from turpentine to pine tar. The
trees delivered to us after cutting were infested with various beetles
and had some fungal growth. I treated them with antifreeze outside under
a plastic tarpaulin every few days for three weeks. They were then free
of insects and fungus and have remained so after being moved inside and
installed in an exhibit over four years ago.
I took three pieces from a rotting dock float that
were covered with a heavy growth of fungus, lichens, etc. I treated one
with antifreeze painted on with a brush, the second with a water
solution containing 23% borates (as B2O3), and left the third untreated
as a control. They were left exposed outdoors and were rained on the
first night. By the next morning the growth on the antifreeze-treated
piece was definitely browning and the borate-treated piece showed slight
browning. After two months exposure to the weather the growth was dead
on the antifreeze- and borate-treated pieces and flourishing on the
control.
I have a simple flat-bottomed skiff built of
plywood and white pine, which has little resistance to rot. After ten
years some rot developed in one of the frames. It may have begun in the
exposed end grain. It consumed the side frame, part of the bottom frame,
and part of a seat brace fastened to the side frame. The plywood gusset
joining the side frame to the bottom frame was not attacked. I excised
the rotted wood, saturated all with ethylene glycol antifreeze to kill
all the rot organisms, and there has been no further deterioration in
four more years afloat with wet bilges. I have not replaced any pieces,
as I am building another boat that can replace it; that is more fun,
anyway.
I have a 60+-year old case of the fungus infection
known as "athlete's foot". Many years ago it infected the toenails
extensively. The whole thing was pretty grotesque. My dermatologist and
druggist both assured me there is no known cure. About six years ago I
started using antifreeze applied under the nails with a medicine dropper
about every five days. The professionals are technically right. I have
not completely cured it, but the nails have grown out pink and thinned
almost to the ends and I never have any trouble with blistering,
peeling, or itching between the toes as I had had for six decades. No
drug company is going to have any interest in this because the
information has been in the public domain for so long that there is no
opportunity for any proprietary advantage. The various wood-rotting
organisms cannot be anywhere near as tough.
There are two types of borate products
commercially available for treating wood-solid sodium octaborate for
making solutions in water (Tim-BorŽ and Ship-BorŽ) and a 40% solution of
sodium octaborate in ethylene glycol (BoracareŽ). Their equivalents and
more concentrated solutions can be easily prepared from borax, boric
acid, and antifreeze at much lower cost. Keith Lawrence, editor of
Boatbuilder offered to sell me advertising if I wanted to go in
the business, but I might run afoul of patents (preparation for
individual use is not prohibited), I would have to get EPA registration,
and I could not deliver products anywhere near as cheaply as they can be
made from raw materials available at your supermarket, drugstore, and
discount store.
Glycol by itself has one big advantage over
solutions of borates in either water or glycol. Glycol penetrates
rapidly through all paint, varnish, and oil finishes (except epoxy and
polyurethanes) without lifting or damaging those finishes in any way.
You can treat all of the wood of your boat without removing any finish.
The dyes in glycol antifreeze are so weak that they do not discolor even
white woods. Once bare wood has been treated with glycol or the borate
solutions and become dry to the touch it can be finished or glued. If a
borate solution leaves white residues on the surface, it will have to be
washed off with water and the surface allowed to dry.
This is my preferred process to treat rot. Once
you find soft wood or other evidence of rot, soak it with antifreeze
even if you cannot do anything else at the moment. Paint it on or spray
it on with a coarse spray. Avoid fine mistlike spraying because it
increases the likelihood that you will breathe in unhealthy amounts of
glycol. Put it on surfaces well away from the really damaged wood, too.
Use glycol lavishly on the suspect wood, which will readily absorb
10-20% of its weight of antifreeze.
Next dig out wood that is rotted enough to be
weak. Add more glycol to wet the exposed wood thoroughly. Then add the
25% borate solution of the recipe below so long as it will soak in in no
more than 2-3 hours. Then fill in the void with epoxy putty and/or a
piece of sound treated wood as required. The reasons I use borates at
all are: 1) it is a belt-and-suspenders approach to a virulent attack,
and 2) over a long period glycol will evaporate from the wood;
especially, in areas exposed directly to the sun and the high
temperatures that result.
If there is any question about water extracting
the glycol or the borates, you can retreat periodically with glycol on
any surface, painted or bare, and with borate solutions on bare
wood.
Glycol's toxicity to humans is low enough that it
has to be deliberately ingested (about a half cup for a 150 lb. human);
many millions of gallons are used annually with few precautions and
without incident. It should not be left where children or pets can get
at it, as smaller doses would harm them, and they may be attracted by
its reported sweet taste that I have confirmed by accident. The lethal
dose of borates is smaller than of glycol, but the bitter taste makes
accidental consumption less likely.