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-Bor® and Ship-Bor®) and a 40% solution of
sodium octaborate in ethylene glycol (Boracare®).
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. IN THE YEARS SINCE I FIRST WROTE THIS ARTICLE, MY EXPERIENCE HAS BEEN THAT GLYCOL BY ITSELF IS GENERALLY THE BEST TREATMENT FOR KILLING ROT. Gougeon's research has shown that borate solutions
weaken epoxy joints in the treated wood. 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.
If you decide you need to treat
with both glycol and borates, 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.