Hi Ryan
Welcome to the "Rebels in progress" clan!
Corrosion protection is a key issue with many Rebel builders and leads to
plenty
of spirited discussion and even differeing opinions, I'll toss mine out here
to
start the thread and let the others join in. When we started our Elite we
faced
this issue and eventually settled on a paint system from Dupont availible at
your local auto part jobber. Our road to this choice is outlined below.
CHEMICAL TREATMENT:
According to best information, aluminum parts should be treated by a
"chromic
conversion coating" process. These are chemical processes
which leave a gold tint (actually a thin oxide layer) on the bare aluminum.
It
is more resistant to corrosion and paint sticks better. These are
known by trade names such as "Alodyne" and "Irridite". These materials are
availible in bulk, unmixed (airplane size) quantities from industrial
distributors and premixed in smaller quantities from automotive body repair
supply dealers (UAP, Autopro). This treatment is then covered by some
primer/paint treatment.
When you talk to the industrial distributors for bulk chromic conversion
coating
materials they do not really want to discuss the material if you are not a
licensed facility because handling the chemicls and disposal of the waste
products is regulated. This is a clear indication that it is not worth the
trouble to do this process in the home shop. We eventually found a shop who
offered this process to the "public". We had some parts treated but since
that
time they have closed the business and moved. Because they have closed and
we
do not want to do this process in our shop we will not treat any more parts
this
way.
PRIMERS:
Traditionally, aircraft manufacturers used zinc chromate primer for
aluminum.
This zinc chromate primer is said to be carcinogenic (!) and some
have said now that newer epoxy paints are better. I spoke to a facility
which
repairs military aircraft who said they no longer use this type of
product due to the health and environmental hazzards. I spoke to a
manufacturer
of floats who does not use this material either.
The favored materials seem to be epoxy primers, some with and some without
chromate in the paint. The military aircraft repair facility uses
alodyne then the epoxy primer and then a polyurethane top coat. I can give
you
specific information if you want it.
We eventually chose a material from Dupont called Corlar 810R. This is an
etching wash primer containing chromate and is availible
from automotive body repair supply dealers. On the data sheet it
specifically
says treatment with chromic conversion coatings prior to priming
is not required. The float maker I spoke to and a light aircraft paint shop
I
spoke to both use 810R. Dupont recommend covering this material with a high
solids primer called 1020R or 1044R. The difference between these is only
color. We plan to use another compatible Dupont top coat called Imron. It
is
said to be important to choose one manufacturer of paint products and stick
with
a compatible "system" within that manufacturer to ensure the paint will stay
where it is put!
Dupont also have a version (820R) which requires chromic conversion coating
prior to priming.
A side comment. In this forum you will get many opinions
including that you should use the green epoxy which comes with the kit and
use
it to "glue" pieces when you rivet them together. We chose to
not do this for a number of reasons. First, while the material is an epoxy
primer it does not state on the package that it is a chromate and if I
recall
corectly I spoke to the factory and they confirmed this but I am not 100%
certain. It also does not etch the base material for adhesion like the
Corlar.
Finally, it is not readily availible like the Dupont products.
We made our decisions based on this information including consultation with
the
Dupont Tech. center and local aircraft refinishing resources, if you find
better
information, we would like to hear about it also.
By the way, I spoke to someone at Cessna, he told me that they do chromic
conversion coating and priming of all piece parts prior to assembly
for their light aircraft (172 etc.). I did not ask what they do to keep
water
from entering through the seams, that would seem to be an important
concern that we have not addressed yet. Our local EAA chapter "guru"
suggests
applying Proseal/PRC after assembly as he did on his RV-4.
I suspect somthing like the more liquid pro-seal or other type of material
would
be useful if "painted" on the seams just prior to assembly. Perhaps
automotive
seam sealer applied during or after assembly would be good. It could be
wiped
off until just a small amount was left to seal the joint.
SHOP PRACTICE:
When we apply these primers we do it using a spray gun in our garage and
remove
the vapors with a powerful fan. The fan actually lowers the
pressure inside the garage so that fresh air is forced in. We also use a
fresh
air system (a hose from the output of a shop vacuum cleaner located in an
area
of fresh air) to provide clean air to breathe (inside a hood) for the person
painting. This is MOST important because the normal "painting gas masks" do
NOT
filter the isocyanates from the fumes of the paint. Isocyanates are part of
most epoxy or two part paints and are very serious! This is the same basic
material you find in Crazy glue etc.
The vendor of each of these materials, when requested, MUST provide you with
a
Material Safety Data Sheet (MSDS) describing toxicicity
and handling information. These will permit you to understand safety of
these
materials.
Back to the rivet question, we dip each (and every !!) rivet in Corlar (not
quite up to the bottom of the head) prior to installation and install wet.
theory being that the wet paint will go into all the gaps of the joint.
Don't
forget though that you still have the end of the steel mandrel exposed to
the
atmosphere (although down in the hole in the rivet), it will need to be
treated
in some way such as your external primer/top coat.
On painting the inside of everything, we are doing that (and assembling dry
like
Cessna) but don't do the insides of the fuel tanks or anywhere the sealer
(proseal) will be applied. We haven't gotten that far but those that have
will
be clear to tell you that you don't want to chance the proseal not sticking.
On your elevator/stabilizer question I will let the Rebel builders comment
on
this since our Rebel is an Elite and is built differently.
Well, that is about it for now, hope this is helpful in getting you ahead on
your decision making!
Dave R.
Ryan Amendala wrote:
All,
Just picked up our kit (Rebel #669) this weekend (can you see the huge
smile
on my face) and have been reading ahead in the manual with some questions:
1: Chromate. Apparently an overlooked item by us. We were surprised not
to see it in our kit. Can you buy this form local auto paint shops or do
you have to order it?
2. Salt Water application. I have read some archives on this. Seems as
though some people dip every rivet and spray the inside of panels with
chromate for heavy salt water use. My question is then, Do you spray the
inside of EVERY panel before assembly including the entire inside of the
wing (excluding tanks), ailerons, elevators...? If so do you spray say
the
top skin before you put in on and then let it dry or do you apply chromate
and immediately install top skin? We do not plan on painting the outside
at
this time we are trying to save on weight.
3. Elevator/stab construction: Reading this I was wondering if it is a
good idea to build the stab before installing the elevator tip? The
instructions say to make sure that the leading edge of the stab should be
even with elevator tip but if you follow instructions you do not have a
leading edge to reference to.
All parts have been inventoried, building starts as soon as we get our
tools
from ATS.
Thanks in advance
BB&R Amendala
Rebel #669
Long EZ N666BA
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