The Murphy Builders Site

You can search the archives on the keyword 'corrosion',
or 'Northern' or 'Boeing' for several messages about this -
corrosion prevention is a frequently recurring question !

Northern Shield is a liquid, blown into finished structures
using a 6 ft. wand with holes, so it comes out as a fine mist. The
mist droplets drift into all the corners, settle out, and spread
to cover the surfaces, creeping into cracks & joints. The solvent
evaporates from the solution over a few days, and you are left
with a permanent, waxy coating that remains flexible, but
prevents oxidation. It is used as a rustproofer in cars, trucks,
boats, and aircraft. It is still best practice to use the
Polyfiber Epoxy Primer in the joints, fastened WET ... you
can use the Northern Shield later if you want. About $40 will
do a complete airplane.

The Boeing product (D-29 ??) is a 2 part solution -
the first part is sprayed in as a mist & allowed to creep for
a day or so, then the 2nd part, a hardener, is sprayed in.
This also leaves a thin, flexible coating on the large surfaces.
Much more expensive than other solutions, but permanent.

D-50 is basically an oil-like product that is sprayed in,
and drips out over a couple of years. Besides needing replacement,
it is messy, continuing to drip for months, and can prevent paint from
sticking on the ouside where it has dripped. Because it stays wet,
it can attract & hold dust, which could hold moisture & add weight.
Personally, I would not use it.....

If you are really worried about it, you can spray (with
proper breathing apparatus only !!) a thin (enough so you can still read
the lettering on the aluminum sheets) coating of Epoxy Primer on
all the large surfaces inside the tail & fuselage bottom, after
installing the ribs & bulkhead using wet Epoxy in the joints.
I strongly suggest spraying, as brushing will most likely give
too thick a coating, which could then crack.
In reality, the fuselage will likely last longer than you !!
There are lots of 50+ year old Cessnas still flying, and they had
NO corrosion protection !!!

..... bobp

----------------------------orig.-------------------
On Sunday 04 April 2004 11:50 pm, you wrote:

Bobp said "You can always blow in a mist of
Northern Shield or Boeing D-29, or similar, AFTER everything is assembled"

I

had never heard of this. Can you give any more details? Is this an
alternative to painting/priming for the major portions of interior

surfaces?

I still don't know if I should be worried about this as much as I am, but I
definately see saltwater in my future.


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