Subject: Re: baidarka Finishing wood on a kayak frame
From: Glenn Stauffer (stauffer@voicenet.com)
Date: Wed Mar 15 2000 - 20:55:13 EST
I understand that thinning also helps draw the oil deeper into the wood.
One web site I found that discussed oil finishes talked about using 50%
thinner, 40% boiled linseed oil, and 10% polyurethane for the first two
coats and then using following coats with progressively 5% less thinner and
5% more poly per coat, but not going below 30% thinner.
I've also read that raw linseed oil imparts a harder finish to the wood than
boiled linseed oil. My experiece is that raw linseed oil takes nearly
forever to dry - heat helps speed the process.
Glenn
----- Original Message -----
From: "albert.runyon" <albert.runyon@MCIWORLD.COM>
To: <baidarka@lists.intelenet.net>
Sent: Wednesday, March 15, 2000 6:54 PM
Subject: Re: baidarka Finishing wood on a kayak frame
> The "boiled" linseed oil already has dryers in it. Adding Japan dryer
may
> be okay but is some duplication of effort. The thinning recommended will
also
> help linseed oil "dry'. If you put too much unthinned oil on the wood it
gets
> sticky and takes forever to dry. Someone mentioned heating the wood as
opposed
> to thinning: probably has merit. Years ago I made some dugout models and
> burned the inside for a realistic look; The oil soaked in like the
> wood(cypress) was a sponge! I always thought it was the charing and didn't
> realise it could be the warm wood.
> I thinned with turpentine as that is traditional, recommended and
worked
> very well.
> As for Tung oil; it is also used in marine finishes; in fact some
"teak oil"
> is mostly tung oil. There are web sites describing all these products.
> Some of the traditional boatbuilding sites have some really great
info.
> Good luck--Al
> "Peter A. Chopelas" wrote:
>
> > I'm at the stage of finishing the wood frame and I have a question I
wonder
> > if anyone can answer:
> >
> > It appears the most common practice is to use thinned boiled linseed oil
> > for the first coat for good penetration, and then another coat of strait
> > boiled linseed oil. I know that linseed oil does not "dry" but rather
> > cures by absorbing oxygen into the polymer matrix, cross linking the
long
> > chains and therefore hardening. Japan dryer works as a catalyst to
speed
> > this process, though I suppose it too leaves a residue in the finish
once
> > cured.
> >
> > There are three common thinning agents: paint thinner, which is
cheapest,
> > turpentine, and naphtha which is also supposed to speed drying.
> >
> > If these all simply evaporate out leaving a thinner layer then I would
> > think the cheapest would be best but no one recommends using paint
thinner.
> > Someone told me that the residue left behind in the finish will cause
it
> > to break down faster and therefore it should only be used for cleaning
> > brushes, etc.
> >
> > Turpentine is derived from pine trees but also works the same way, it
> > simply thins the finish and evaporates out, though I imagine it leaves
some
> > residue as well. Naphtha is similar in cost but I would presume it is
> > chemically different, does it have a catalytic effect or is it simply
that
> > thinning the finish allows more air to come in contact with the matrix?
It
> > the chemical action any different than Japan Dryer?
> >
> > What are the chemical differences between paint thinner, turpentine, and
> > naphtha and when would I want to use one over the other? What long term
> > effect if any is there to the finish caused by the residue from each of
> > these, and the Japan dryer? Do any make it more durable, or reduce its
> > life, change it's color, etc.? Is there any toxic residue left in the
> > finish from each of these, including the Japan dryer, that I should know
> > about?
> >
> > I've also recently learned that it was discovered that the boiled
linseed
> > oil (and many oil based paints for that matter) will actually promote
mold
> > and mildew formation. This is believable since the lighter fractions of
> > the oil that get trapped in the matrix but do not actually chemically
take
> > part in the cross linking could indeed "feed" mold. The mildew
resistant
> > paints and the expensive "bottom" paints simply have toxic chemical
> > additives to kill any micro organisms, therefore would adding the
fungicide
> > available in paint stores for this purpose to the boiled linseed oil be
a
> > good idea?
> >
> > If so does anyone know enough about the chemistry of this additive to
know
> > how it may affect the long term durability of the finish? It is fairly
> > toxic stuff but is there any concern with its toxicity after the finish
is
> > cured?
> >
> > Is there any common and inexpensive additive to make the finish more UV
> > resistant? I read some old time wood boat builders add pine tar to the
> > linseed oil, this will darken it but does it have any other effect on
the
> > finish over the long term, making it last longer or more UV resistant?
> >
> > Also I have a quart of pure tung oil finish in the paint cabinet, which
is
> > derived from "tung" trees, and I was wondering how good a boat finish
that
> > would make. Does any one know how it holds up for use in kayak frames,
> > etc.?
> >
> > Most of the salesmen in the paint stores can not answer these questions
and
> > I find it useful to understand the chemistry of what I doing so I can
judge
> > if I may want to make adjustments to mix, and I would also like to know
> > what the practical, long term experience people may have had with this
> > stuff since knowing the chemistry does not answer the real important
> > questions, like will it have some undesired long term effect.
> >
> > I know some people use polyurethane finish on the wood frames but I
think
> > this would be a mistake, the finish is harder but also more brittle and
> > will shrink and crack as it ages. Not good on a flexible frame in a
marine
> > environment, the boiled linseed oil would be superior, I just want to
> > understand more about it.
> >
> > Peter
> > Arlington, WA
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