Priming/Coating parts-proximity to salt water

tomhanaway · #1 10-01-2006, 07:42 PM

OK guys,
I live in Boynton Beach, FL and have jumped in by ordering my Rv-10 empennage package. I've read through many of the multiple threads re: priming/coatings and am already confused.

Assuming all goes reasonably well, and the plane is ready to fly sometime in the far future, I'll have it professionally painted.
My question relates to priming/coating of parts while being assembled. Given that we have the salt water environment, and different aluminum parts contacting one another may be a petri jar for corrosion,
what are the South Florida builders using/doing???
Is there a primer thread that you found particularly useful for builders close to salt water/air?

Question 1 of the many hundreds to come.
Tom Hanaway
Boynton Beach, Fl

AntiGravity · #2 10-01-2006, 08:16 PM

Can't help you with the whole Florida thing, since I'm in New Zealand. But where I live is a particularly wet place.

I looked at it this way:

If I didn't prime and got corrosion some time down the track, then I'd be pretty peeved and wonder whether the whole alodining/priming thing would have been worth it, and would have saved me the hassle/cost of repair work.
On the other hand, if I alodine & prime (which I am) and I still get corrosion, then heck, it was gonna happen anyway, but maybe I bought myself some extra time.

Primer weight, for me, was not an issue. I'd rather have a slightly heavier plane that lasts, than one that costs me an arm and a leg to repair in xx years time.

It's an insurance thing...

Cheers,

N62XS · #3 10-01-2006, 08:25 PM

After the dimple/drill/fit process, I plan to apply an AlumiPrep/Alodine treatment, followed by a Eposy primer prior to joining any part together. I will be living about 3000' from a saltwater sound in coastal Georgia. I too will appreciate any constructive advice.

az_gila · #4 10-02-2006, 01:09 AM

Quote:

Originally Posted by Hard Knox

After the dimple/drill/fit process, I plan to apply an AlumiPrep/Alodine treatment, followed by a Eposy primer prior to joining any part together. I will be living about 3000' from a saltwater sound in coastal Georgia. I too will appreciate any constructive advice.

Robby... the specification for the MIL-P-23377 primers - and the Boeing proprietary specification primers (e.g. Akzo from Aircraft $pruce) - calls for a properly prepared 2024 alclad panel to take 1000 hrs of hot water salt spray with no corrosion. It even calls for a scribe in the primer before the test, and no corrosion must exist in the scratch at the end of the test.

Proper preparation is defined as an acid etch and alodine. The alodine is sacrificial, so this keeps the "no corrosion" bit true in the scratched part of the primer during the salt spray.

This preparation is good enough for the recently retired F-14s on board carrier decks, so is probably good enough for FL.....

This is the advantage of following Mil Specs. - the quality of the final job is known if the procedures are followed...

gil in Tucson... a little drier than FL...

mike newall · #5 10-02-2006, 02:06 AM

Ooo, goody, Primer Wars is back !

We live in England where we get average summers and moist winters so corrosion protection is important and yes, our forums get a good dose of primer concern from time to time.

When you visit your local airport, whether it is in Florida, Maine or UK and look around, the fleet of aging Cessnas and Pipers are not falling apart from corrosion. Some have factory corrosion protection, some have none.

You have to be careful not to go over the top and end up going through so many processes as to slow your build to a crawl, expose yourself to some rather dangerous chemicals and finally to allow the weight to grow without any need.

If in doubt, go back to basics and ask what did the commercial manufacturers do and what does Van's suggest. Either way, you usually come up with some basic protection for the inside skins using a paint or sealer that slows down the action of corrosion. Don't forget, the coating of aluminium over the 2024 is very effective at stopping corrosion by itself.

Above all, be careful, some of the chromic conversion chemicals are toxic in multiple ways. Heavy metal toxins build up in the body and do not get passed through the system.

So, back to the original question.

Find an easy to apply, simple, low toxicity primer( we use a 2 part acid etch primer for the auto industry, not epoxy, carbon mask only needed), spray the inside surfaces, pay attention to joints of dissimilar metals and a light smear of joint compound is all that is needed there. Finally, if you want belt and braces, when all is finished and painted, an internal spray of something like ACF50 will guarantee that your bird will outlast you and the next 3 owners !

Captain Avgas · #6 10-02-2006, 02:59 AM

Quote:

Originally Posted by mike newall

When you visit your local airport, whether it is in Florida, Maine or UK and look around, the fleet of aging Cessnas and Pipers are not falling apart from corrosion.

Yes they are. And that's specifically why Cessna, Piper and every other reputable manufacturer of certificated metal planes now internally primes fully with phosphoric acid etch, alodine, and BMS10-11 strontium chromate two pack epoxy (Boeing spec). They learnt from their mistake.

cytoxin · #7 10-02-2006, 06:05 AM

telling them i was priming they said they would prime everything they could. 75 miles from the coast. you'll get the 50 year old cessna no prime

but do what pleases you. i did most of mine and wish i would have primed more. all ribs, steel,bar stock, and rivet lines on skin. alumna prep alodine and akzo or nason ful poxy...YMMV

all the old 150's ive flown have had alot of faying surface corrsion (mid 70's birds)

captainron · #8 10-02-2006, 06:26 AM

Hi Tom, Glad to have another builder in the area. I'm right up the street. There are several other builders close-by, too. I have a QB -7, and am trying to figure out the primer issue also.

TSwezey · #9 10-02-2006, 10:34 AM

Our plane will be kept at Savannah. It is surrounded by swamp and salt water. Most of the places we will be flying to are also surrounded by saltwater.
We are following the procedures that I believe is used by Gulfstream and other jet manufacturers.
We light sand the aluminum and then apply alodine.
The alodine we are using is Alodine per MIL-C-5541, Class 1A.
We then prime.
The primer we are using is manufactured by Deft. It is a 2 Part, Green
Epoxy, Polyamide Primer (44-GN-11 Base/Catalyst). It is both chemical and
solvent resistant. It meets Boeing Specification BMS-1011. It is used by a
number of jet manufacturers (Boeing, Gulfstream, and Bombardier are three
that I know of that use it). It has two benefits: 1.) It is water soluble,
which makes cleanup easy. 2.) It is rated as low-VOC (Volatile Organic
Compounds) for air quality and health.

The company web site is: http://www.deftfinishes.com

We are applying proseal to every location on the airplane that two pieces of metal come together when we rivet. Basically our plane is sealed just like the fuel tanks. Is this excessive? I don't know but there are many planes that come back to Gulfstream with corrosion problems. Our plane will probably stay together without the rivets!
The building process easily doubles the build time of the plane but chances are I will be long gone before this plane has any corrosion.

Just my two cents and how we are building it.