Agreed, Ron, there are several ways to do the job. My main point was that
aluminum MUST be treated in some fashion in order to make any paint adhere.
In your link to dplf-p-196 the footnote for painting aluminum addresses this
point, "+ Film build of 1.2-1.5 mils of DPLF is required or the surface must
be treated with Metal Cleaner/Conditioner or coated with DX 1791/1792."
However, in my view, MIL-DTL-81706B makes a rather strong case for using a
conversion coating prior to painting. Links to this specificaiton and other
relevant stuff are available at
http://www.chemical-supermarket.com/Henkel_Alodine_1201_Chromate_Conversion_
Coating-p364.html
Alodine provides corrosion resistance and promotes adhesion of the
subsequent organic coating to aluminum, and its application is relatively
quick and painless. True, we are playing with chemicals here so a certain
amount of caution is required but the chemistry is nowhere near as hazardous
to work with as oven cleaners or drain cleaners. Henkel, incidentally, is
the owner of the Alodine trademark.
Best regards,
Rob Housman
Irvine, California
Europa XS Tri-Gear
S/N A070
Airframe complete
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of
rparigor@suffolk.lib.ny.us
Sent: Tuesday, May 08, 2007 2:38 PM
Subject: Europa-List: Painting metal parts
Hello Rob
There are more than 1 way to skin a cat or paint metal on a Europa. If you
read the link you posted:
http://www.ronjoseph.com/Q&A/B2001_painting_aluminum.htm
bout half way down:
Q: What would a common procedure be to resurface a corrosion pitted marine
motor outdrive (mercury-aluminum outdrive). I have heard that 2 part
paints and epoxies have incredible adhesive properties as well as
corrosion resistance, but what would be recommended in this application?
A: An epoxy primer followed by a polyurethane topcoat is still my number
one choice, but the real issue is cleaning up the pits in the motor
outdrive. Once the pits have been thoroughly cleaned, your friend will
need to immediately apply the epoxy primer. By immediate, I mean within a
few hours and not the following day. One method to clean the pits and
prepare the surface is by abrasive blasting with glass beads. But your
friend will probably need to take the drive to a ob shop to have this
done. In the industrial world the drive would probably be pretreated with
a chromate conversion coating, but in all likelihood your friend won't
have access to this process, unless he/she is willing to take the drive to
a job shop that has the capabilities of pretreating aluminum. (Many job
shops can blast clean the surface with glass beads and pretreat in a
conversion coating).
Glass beading is very bad advise though. Glass beading creates rounded
scratches that do not bode well for adhesion. Sharp media is needed.
Downside to 2 part Epoxy or powder coating is like stated you must paint
shortly after you sand. You can apply DPLF over Alodined parts though. If
acid creeps somewhere it is not supposed to be and you can't get it out
that will do no good for the long term.
I provided link for manual for paints, here is one for DPLF:
http://www.pwpaints.com/images/downloads/dplf-p-196.pdf
1 note on self etching zinc primers, they use acid to etch the surface,
half or more of the magic provided by zinc is used up to neutralize the
acid! I know many folk coat aluminium with zinc primer, but it is porous
and for best corrosion properties, sealer is needed.
PPG and Dupont have technicians you can talk to, whoever system you
choose, don't be bashful to call. Or if you are going to have your plane
painted by someone, now is a good time to perhaps talk to a few shops and
get their opinion on painting various materials and what to use.
No matter what you decide, try on something other than your aeroplane
parts first, and always have a sample you can do a scratch test then heat.
You will learn a lot, 3M 375 packaging tape is pretty aggressive, use it
to try and lift paint, use dental tools for adhesion testing.
Ron Parigoris
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