From: Craig Wall <corax@concentric.net>
Subject: Re: tube notching, how?
Date: 26 Dec 1998
Newsgroups: rec.aviation.homebuilt

DEADAIM10X wrote:

>
>
> Now as to coating the inside of the tube with linseed oil: I have discussed
> this topic with many an "olde timer" and get this difference. Some say use raw
> linseed oil because it never hardens and continues to flow the areas of need
> for the life of the fuselage. Others say to use boiled linseed oil because it
> clots and plugs any pinholes in the welds preventing moisture from getting
> inside via barometric pressure changes.

  The confusion over "boiled" versus "raw" linseed oil is a source of a
lot of misinformation. Both will harden, given continuous exposure to
oxygen.  Both will not if oxygen is not present, though raw will come
closer.  Both will seal pinholes.

  "Boiled" is not what most people think; it should actually be called
"de-gassed" since the "boiling" is done by vacuum at room temperature.
It just takes the dissolved air out (the "boiling" is just the gases
expanding and breaking as bubbles), and makes the linseed oil less likely
to cause spontaneous combustion when oily rags are left wadded up.
(Remember "spontaneous combustion" warnings about oily rags? They never
managed to mention that linseed oil is the *only* oil you need to worry
about, and the only oil you were likely to generate oily rags with that
you were likely to store wadded up overnight for use the next day.) It
also forms less gum on standing due to crosslinking in bulk storage.

  BTW, I swear by linseed oil as an anti-corrosive coating.  I use it on
aluminum, *especially* externally where there have been white patches- I
sand off the white oxide and then coat with a thin layer of linseed oil
to occlude and passivate pinhole craters.  It weathers away and need to
be reapplied, though you can get it off quickly with a little paint
remover when you need too.

  Craig Wall