Zinc Chromate vs Zinc Oxide

[mhorowit]

I see Aircraft Spruce offers Zinc Oxide as well as Zinc Chromate; the former being more environmently friendly.

I understand two-part epoxy can be placed over the chromate; can it just as well be placed over the oxide? The literature says the oxide meets MIL SPEC TT-P-1757, but that spec was probably developed long before two-part came out. - Mike

[Winston L.]

Re: Zinc Chromate vs Zinc Oxide

Taylorcraft originally used yellow zinc chromate on your airplane. Yes, you can prime just about anything with epoxy primer. Use the stits epoxy primer though because I haven't found another epoxy primer that is resistant to the M.E.K. based adhesive.

Winston

[N96337]

Re: Zinc Chromate vs Zinc Oxide

Taylorcraft originally used yellow zinc chromate on your airplane. Yes, you can prime just about anything with epoxy primer. Use the stits epoxy primer though because I haven't found another epoxy primer that is resistant to the M.E.K. based adhesive.

Winston

Yep, the Polyfiber Epoxy Primer is awesome stuff! I wouldn't waste my time with any of the available (in the US) "zinc chromate" primers....
JH

[Ragwing nut]

Re: Zinc Chromate vs Zinc Oxide

Chromate was banned from paint along with lead years ago. The primer today only has the name. I also am a supporter of Stits epoxy. Expensive but worth it. Any spray can paint you buy has very little protective value and in today's age I would only consider a 2 part catalysted paint.

Mike

[mhorowit]

Re: Zinc Chromate vs Zinc Oxide

Guys - let me explain what I'm trying to do and that will explain why all these questions.

I'm going to be removing old glue/paint/primer off pieces for a long time. For two reasons I don't want to initially apply epoxy primer: First, the expense and second, the shelf life of an open catalyst is only a month.

I'm thinking I can apply zinc chromate/oxide on everything as I go, and then put a coating of epoxy over those parts that had previously shown rust damage(plus all of the fuselage). That way everything is protected until I'm ready to apply epoxy to specific parts.

Now today’s posts concerning the effectiveness of today’s Zinc Chromate primer has set me back. I’ll need to check the statement that today’s Zinc Chromate won’t do what I’m expecting it to do. Consider this however; if today’s Zinc Chromate primer says “Meets MIL-SPEC TT-P-1757”, which is the one for the 1945 primer, shouldn’t the effectiveness be the same?

- Mike

[Winston L.]

Re: Zinc Chromate vs Zinc Oxide

It still does the job it is supposed to. The only thing is you can't use it where fabric is going to bond like you used to. The new zinc chromate does not have as many solids as the old stuff, therefore it isn't dope proof. You can use zinc chromate, by itself, on internal parts, where the fabric will not come in contact with it. I would prime the steel parts that you blast with any primer you can get your hands on if you are going to epoxy prime later.


Winston

[mhorowit]

Re: Zinc Chromate vs Zinc Oxide

It still does the job it is supposed to. The only thing is you can't use it where fabric is going to bond like you used to. The new zinc chromate does not have as many solids as the old stuff, therefore it isn't dope proof. You can use zinc chromate, by itself, on internal parts, where the fabric will not come in contact with it. I would prime the steel parts that you blast with any primer you can get your hands on if you are going to epoxy prime later.


Winston

Sure!! You're talking about the incompatibality of the new adhesives to the old primer. No problem. - MIke

[Mark Julicher]

Re: Zinc Chromate vs Zinc Oxide

Mike,
Primer makes the top coat stick. Steel parts can still rust (albeit much slower) when they are primed with zinc-xx and left to sit around. A lot depends on humidity, hmmm N. Virginia is not exactly Arizona in that regard. Primer is better than bare metal, and there are non-epoxy primers that are better than zinc-xx. My personal favorite is Mar-Hyde which is available at your local Auto paint shop.

By saying this I have doubtless upset 25 other tribesmen and their favorite steel preservation method (hey, trashing another guy's paint method is worse than insulting his dog). I can take the heat.

Perhaps you can put your (some of the smaller) primed parts in plastic bags with some dessicant or keep them in the house where the humidity is less than out in the garage.

[VictorBravo]

Re: Zinc Chromate vs Zinc Oxide

Mike, get some Rust-Oleum primer or paint in a gallon can at your local home warehouse on sale. BRUSH it on liberally, squeezing it into all the nooks and crannies, making a big gloppy mess. Let it dry and then put the part in a plastic bag. If you have dessicant, put that in the bag too. Mark the outside of the bag with what it it is, and seal it. If you have a food vacuum sealer you can use that too.

When the time comes to put the plane together, sandblast off the Rust-Oleum, then epoxy prime it or powder coat it or whetever you decide to use, and move forward.

The Rust-Oleum is far cheaper than epoxy, and if I recall it is a thick sturdy coating that should protect your parts. Brushing will be far superior to spraying from a cost and breathing standpoint.

If they have a corrosion primer (red oxide would be ideal) then choose that, although their brand of paint is pretty decent at corrosion protection as well.

[mhorowit]

Re: Zinc Chromate vs Zinc Oxide

Mike,
Primer makes the top coat stick. Steel parts can still rust (albeit much slower) when they are primed with zinc-xx and left to sit around. A lot depends on humidity, hmmm N. Virginia is not exactly Arizona in that regard. Primer is better than bare metal, and there are non-epoxy primers that are better than zinc-xx. My personal favorite is Mar-Hyde which is available at your local Auto paint shop.

I don't wanna have to remove primer in order to put down epoxy.
I know I can put epoxy over Zinc XX. (Superflite sez so).

You have anything to support or debunk the feasibility of epoxy over Mar-Hyde?

Haven't I seen lots of parts primed with zinc chromate but not top coated?

- Mike

[fearofpavement]

Re: Zinc Chromate vs Zinc Oxide

quote:
Haven't I seen lots of parts primed with zinc chromate but not top coated?

Aluminum yes. Steel needs paint. Even red oxide will rust through if not topcoated.

[Forrest Barber]

Re: Zinc Chromate vs Zinc Oxide

anybody use DuPont Vari-Prime?? cute little spray can OR mix it and go.

[N96337]

Re: Zinc Chromate vs Zinc Oxide

I don't wanna have to remove primer in order to put down epoxy.
I know I can put epoxy over Zinc XX. (Superflite sez so).

- Mike

Mike, here's something to ALWAYS keep in mind with painting.... the topcoats are only as good as what is under them!! Sure, the Zinc XX may not wrinkle up and completely reject the epoxy, but I'll bet ya some $$ that it's not as durable nor does it have as good adhesion properties as the epoxy does... NO single part paint will... therefore why waste the time putting epoxy over it??? It's only as good as what it's applied over.
As far as epoxy being a pain to apply, just keep the parts stripped, dry, and when you get a few, paint the whole bunch. You can stretch the life of epoxy catalyst a long, long time, if you keep a really good seal on the can. I try to buy catalyst in the smallest container that they offer, unless I know that I'm going to be using a bunch at once (like a fuselage or something)
I usually always throw the catalyst can in a ziplock bag as soon as it's been used once, and work all the air I can out of it before sealing the bag. Take a good CLEAN rag and wipe the lip of the can, and the lid everytime you use it... and if you can, keep the catalyst in a cool, dry place, and it will suprise you how long you can use it. Don't worry, it will tell you when it's no good anymore!
JH

[Ragwing nut]

Re: Zinc Chromate vs Zinc Oxide

Mike, Variprime will work for what you want to do as Forrest said. Now that you have clarified you actions, when I have steel parts sand blasted that I can't immediatley go straight to epoxy with, I Variprime them. Variprime is a Dupont product, but Nason has an acid etch primer cheaper that does the same. It conditions the metal to accept primer. I have 2 Cub fuselages in Variprime now while I am making all the repairs to them. Once done, scotch brite, and epoxy prime and your ready to go.

Mike

[Forrest Barber]

Re: Zinc Chromate vs Zinc Oxide

Nason? tell us more Old dogs love new tricks