primer weight?

[gmcjetpilot]

Originally Posted by chaskuss

George,
Have you ever actually read the application instructions for the various brands of polyurathane paints? If you actually had, you'd know that they call for a 6 mil coating (2 coats) of finish paint. Assuming a MilSpec (1 mil) application of primer, that means the primer is only ONE SEVENTH of the weight of the complete paint job. Let's see, ... 30 pounds divided by 7 equals 4.29 pounds of primer on the exterior. If we assume that priming the interior will add twice that 4.29 pounds, that's quite a bit less than your guesstimate of 25 pounds. 25 pounds of primer sounds reasonable for a sea plane, but not most RVs.
I think you really are overstating what portion of the total weight can be attributed to the primer. If you live in Florida or New Zealand, you had better treat it like a sea plane, because it is. Down here, we have 4 year old RVs (always hangered) which have significant corrosion because the builder didn't use Alodine under the primer. FYI, MilSpec epoxy primers only stop 7 of the 8 types of corrosion. The only thing which stops filiform (the most insideous type) corrosion, is a chromate conversion process (aka Alodine, Iridite and several other brand names). Alodine will prevent 4 of the 8 types of corrosion. Most of this info is available on EAA Chapter 1000's web site.
Charlie Kuss

Not sure what your point is? It decidedly sounds like you are telling me I am not only wrong but ignorant, "Have you ever actually read the application instructions for the various brands of polyurathane paints? If you actually had, you'd know......"

Clearly you are looking for a fight and I am not playing. You don't like my SWAG, OK. Second please don't lecture me about corrosion. I was a lead structural engineer for Boeing at one time. I know more about finishes and corrosion in aerospace materials and structures than you think. I am not going to argue with you. Prime to you hearts content Charles.

I don't buy your 5 lbs, 1 mil thickness for a true protective (sealing) primer by the way. No 1 mil thick primer could stand up to the "Mil Spec" salt spray test that I know of. The Grey Lesonal (german) primer I use recomends min 3 mil build to seal surface.

If you would read my post carefully it starts with SWAG - Scientific Wild A** Guess. Second, I only quote what a FINISH paint job weighs as a data point. Not a trying to make any comparison, except that primer, paint and clear can add 30 lbs, fact. Yes primer alone is lighter, no kidding. Primer is at least a quarter of teh 30 lbs.

So Surface area outside < Surface area inside structure (including sub structure)

This is my point. How much more area inside? I don't know. 100% more? So if primer alone on the outside is 7 or 8 lbs than the inside would be 14 to 16 lbs. OK so my 25 lbs is too high by a factor of 2. I don't really care, but your 4.29 lbs (high precison number) is off by a factor of 3. In a 100 years it will not matter.

If you would have read my post, there are many brands and types of primers. Wash primer is translucent, low solids. Filler primers are applied to greater thickness and weight. What Van uses, wash self etching, does not add much weight. I am not going to get into wheather Van's wash primer is OK as a final coat. I think it is fine and adds some protection, especially since the aluminum is already clad. However other true sealing primers go on way thicker than 1 mil my friend.

For the record, I gather you don't like my comment about float planes. Yes, I don't think Alclad needs to be primed unilateral. Overkill priming is one of the contributing factors to RV's that have 1,250 lb empty weights. Some builders have never seen an extra pound of weight to add they said no to. My RV-7 in a hanger. Even on a coastal city is going to last longer than I need it to. Will any of this matter in a 100 years. Relax. It is not critical like you make it sound. We are not using exotic high strength materials in harsh conditions. Just 2024-T3 clad sheet. Ho hum. You are eggagerating the corrosion issue, even in Florida or new Zealand. You have a better chance of your RV being destroyed by either a hurricane (FL) or a goat eating it (NZ), than getting significant corrosion damage in your life time. But do what makes you happy.

To each his own brother. If you want to prime that is your business, but you are adding weight, more than you think.

There are too many variables to say for sure, but a true primer that is designed to be top coat protection (thick) and "fully priming" ALL THE structure inside a RV can add up to 25 lbs IMHO. May be its half that? Most people apply paint and primer too heavily. There are too many variables.

Clearly you don't like my guess. OK. We agree to disagree. I am going to take a wild guess your RV is primed inside. Right. What is the empty weight of your plane? Respectfully disagree. Have a nice day. Cheers

[markerthebarker]

This has really got me thinking I should use a polished finish

George Henson
RV-10 Empennage Intransit
Regina, SK

[Stephen Lindberg]

Here is a datum for your consideration. I weighted two fuselage skins before and after priming. The primer is DuPont ChromaPremier 22860S Etch Primer. I applied it heavier than George would like but it sure felt (and looks) good. The results? 0.038 ozs./ft. squared.
These airplanes will outlive most of us. I think we should do the best we can to make them useful for the next generation. Case in point: I have in the past year worked on two Ercoupes and a Luscombe repairing corrosion damage. No primer. Charity care in my case, but I got to fly them after I worked on them. For some reason the owners wanted me to fly them first. Anyway, it is my impression that internal surfaces that are primed (probably zinc chromate/lacquer in these old airplanes) has less corrosion than unprimed. I am thinking of Comanches. The curtain is coming down on many Ercoupes due to center section corrosion, from what I've seen. Luscombe tails, too, but they are more fixable. Include me in the primer camp. It is worth a few pounds.

[cytoxin]

as far as akzo i dont think much of it is solvents.(as compared to primers thinned with thinners (dp 40 by ppg thinned 25%by volume for app as a sealer)) i would speculate that if you weighed both cans you could reasonably estimate 1/2 of the total weight. 12 lbs. comes to mind for mine. but here we have huge differences in tecnique and the weight could vary wildly. i have used 1 akzo kit (2 gal total) note the reducer itself dries and leaves a thick sticky film)) and i am almost done priming. if you apply it correctly there is very little overspary..ALOT of people here are priming for the first time and really overdo it. the fluid tip of the gun and psi can reduce the overspray to nil.( the whole concept behind HVLP) you load it up in a large gun i would say it takes twice as much as small touch up gun which sprays a finer mist.as far as production goes it IMHO they waste loads of everything for speed. JMHO
the weight really is determine by film build as we all know already and that is not remotely consistent among builders. i think it is safe to assume 12-25 pounds. just realize most people start off in the tail and as the learing curve takes place thay use less and less.. i dont think my a&p instructor would be happy. he would always say to much in the tail goes a long way and will have you stripping and doing it over

[az_gila]

Originally Posted by gmcjetpilot

No 1 mil thick primer could stand up to the "Mil Spec" salt spray test that I know of.

George.... I'm confused on this statement....

The new MIL-P-23377J specification states...

3.8.2.1 Salt spray. The primer coatings, with and without a topcoat, shall not exhibit blistering, lifting of either coating, nor substrate pitting after exposure to a 5 percent salt spray for 2,000 hours. Class C1 and C2 primers shall exhibit no corrosion in the scribe.

And the spec. calls for a thinner coat than we have talked about here...

3.9.2 Application. The admixed primer coatings shall be capable of being applied by conventional, airless, high volume/low pressure (HVLP) or electrostatic spray equipment. Application shall yield a uniform film with no runs or sags at a dry-film thickness of 15 to 23 microns (μm) (0.6 to 0.9 mil)

e. Spray the test panels with primer coating to a dry-film thickness of 15 to 23 μm (0.6 to 0.9 mil).

It seems to me that 2000 hrs of direct salt spray IS meeting the Mil-Spec, and it has to be either with or without a topcoat.

What data were you basing your comments on??

gil in Tucson ... reads too many specs. for a living....

For those not familiar with the spec. The "scribe" is a scratch in the test sample... note, it's not allowed to corrode even when there is a scratch... this is part of the alodine/chromate "self-healing" effect.
The Classes are described here...
3.4.1.1 Class C1. Coatings containing barium chromate based corrosion inhibitors, along with extenders and other pigments, shall be identified as class C1.
3.4.1.2 Class C2. Coatings containing strontium chromate conforming to ASTM-D1649 as the corrosion inhibitor, along with extenders and other pigments, shall be identified as class C2.


Govt. specs. can be found here for free... your tax $$ at work...
http://assist.daps.dla.mil/quicksearch/

[gmcjetpilot]

Originally Posted by az_gila

George.... I'm confused on this statement....

gil in Tucson ... reads too many specs. for a living....

For those not familiar with the spec. The "scribe" is a scratch in the test sample... note, it's not allowed to corrode even when there is a scratch... this is part of the alodine/chromate "self-healing" effect.

Govt. specs. can be found here for free... your tax $$ at work...
http://assist.daps.dla.mil/quicksearch/

I'm confused as well...

No wounder I got out of engineering. My good friend makes a living in this area and this is what he does, run test and verify or make specs. I am not sure what your question is.

I guess you are talking about the thin film thickness passing the salt spray? If a 0.6 mil thick layer of primer passes the test, that's the primer you want for your RV on floats.

I noticed you mention chromate or typically Zinc Chromate. I am not up on the latest; I thought you could not buy it anymore, but see Spruce A/C sells a "Zinc Chromate" primer? If you are going to prime for a truly severe environment and can get zinc chromate, than by all means get chromate, its awesome. It is also hazardous to your health and the environment. Remember Julia Roberts in the move "Erin Brockovich", about contaminated well water in a small town and the severe health problems of the towns residence. ** Chromium hexavalent was the ingredient in those wells from the local PG&E chemical company. There's a push to eliminate all these carcinogens chemicals. How it stands I don't know. I use epoxy primers with out chromium or zinc. Industries like Pratt and Whitney for example have worked hard to develop chromium free primers.

You talk about "self healing" of zinc chromium, and I know what you mean. Zinc is sacrificial, protecting the base material. Boats put zinc bars on the haul to protect the steel. The chromium neutralize the galvanic process. All good stuff for a wet severe environment. Also very nasty stuff with potential serious health effects.

The NON chromate primers or epoxy sealants can meet the salt spray test I assume by using thicker film thickness, at the cost of weight. I do know zinc chromate is good stuff. I don't think you need it for a RV myself. Sorry if that does not answer your question. There are 100's or primers. Too many for me. I can guess that if you want to use zinc chromate and can get it, than do it with great great care, meaning a fresh air system and dispose of all items contaminated to a hazardous waste disposal site.

This is beyond the scoop of this thread which was what is the added weight to prime ALL internal structure of a RV, every square inch, of every aluminum part, top, bottom, front and back. My 25 lbs may be a high est, 15 lbs is too much. No doubt zinc chromium can go on thinner and provide the same level of protection with it's active (carcinogenic) ingredients. Bottom line, the environment is not severe for a land based RV. I am a liberal when it comes to primers, do what makes you happy, just don't kill yourself with chemicals.


** Chromium hexavalent (CrVI) compounds, often called hexavalent chromium, exist in several forms. Chromates are often used as pigments for photography, and in pyrotechnics, dyes, paints, inks, and plastics. They can also be used for stainless steel production, textile dyes, wood preservation, leather tanning, and as anti-corrosion coatings.

[az_gila]

Originally Posted by gmcjetpilot

I'm confused as well...

No wounder I got out of engineering. My good friend makes a living in this area and this is what he does, run test and verify or make specs. I am not sure what your question is.

I guess you are talking about the thin film thickness passing the salt spray? If a 0.6 mil thick layer of primer passes the test, that's the primer you want for your RV on floats.

I noticed you mention chromate or typically Zinc Chromate. I am not up on the latest; I thought you could not buy it anymore, but see Spruce A/C sells a "Zinc Chromate" primer? If you are going to prime for a truly severe environment and can get zinc chromate, than by all means get chromate, its awesome. It is also hazardous to your health and the environment. Remember Julia Roberts in the move "Erin Brockovich", about contaminated well water in a small town and the severe health problems of the towns residence. ** Chromium hexavalent was the ingredient in those wells from the local PG&E chemical company. There's a push to eliminate all these carcinogens chemicals. How it stands I don't know. I use epoxy primers with out chromium or zinc.


The NON chromate primers or epoxy sealants can meet the salt spray test I assume by using thicker film thickness, at the cost of weight. I do know zinc chromate is good stuff. I don't think you need it for a RV myself. Sorry if that does not answer your question but not sure I understand or know the answer is. Let me make it clear there are 100's or primers. Too many for me. I can guess that if you want to use zinc chromate and can get it, than do it with great great care, meaning a fresh air system and dispose of all items contaminated to a hazardous waste disposal site.


** Chromium hexavalent (CrVI) compounds, often called hexavalent chromium, exist in several forms. Chromates are often used as pigments for photography, and in pyrotechnics, dyes, paints, inks, and plastics. They can also be used for stainless steel production, textile dyes, wood preservation, leather tanning, and as anti-corrosion coatings.

George .... MIL-P-23377 - in it's different versions is the standard military primer. It's part of the Navy spec. for planes (like the F-14s shown previously getting sprayed on an aircraft carrier)

The chromate in these are now strontium chromate, which has generically replaced zinc. We are NOT talking about zinc chromate.

This is epoxy primer, available from lots of sources, that will meet the salt spray test at 0.0006 inches thick. It's not exotic material.

The boat folks use it for metal, as in my previous post from DETCO Marine.

http://www.detcosterling.com/slacgu...CRAFT%20PRIMERS

I published it's wt. per sq. ft. earlier in a 1 mil. thickness. If homebuilders aim for a thin transparent film, then will get the 0.0006 to 0.009 range, but test first...

What I don't understand is your insistence that a 1 mill epoxy primer won't pass the salt spray test. They must to be Mil-Spec. qualified.
When applied over an etched, alondined aluminum material in this thin layer, it WILL meet the MIL-spec. for salt spray.

It's a standard aerospace product.... do a google on MIL-P-23377 and see how many suppliers there are for it in the US.... we are not talking exotics here... and it's still part of the current MIL-P-23377J shown in the earlier link.

It might be hazardous to your health, but so is every sprayed urethane that has an isocynate hardener (such as Imron, and even Centari enamel with a hardener)

gil in Tucson

[gmcjetpilot]

Originally Posted by az_gila

George .... MIL-P-23377 - in it's different versions is the standard military primer. It's part of the Navy spec. for planes (like the F-14s shown previously getting sprayed on an aircraft carrier)gil in Tucson

That is good stuff. I did a quick goggle, I see the specs, interesting. What is the cost? To be honest I did not know about or look at this new spec. Sounds good. Not sure what strontium chromate is, but it must be good stuff. The chromium is an active ingredient. This is not to be sprayed casually with a dust mask either, like any epoxy.

As far as the 1 mil thickness, I stand corrected, 1 mil gives full protection. My LESONAL spec calls for a 1 to 3 mil application, 3 mil to provide max protection. (Lesonal is a high grade product made in Germany.) Even MIL-P-23377 says 0.9 mil is minimum. My primer is not MIL-P-23377. I guess my RV will fall apart in a few years.

To have a weight discussion you have to talk about a spacific product or "system" of protection. Get MIL-P-23377 and apply 1 mil, you get great protection and lighter weight. That is a good thing if you plan on priming everything. That is great info. I still say the surface area of everything inside a RV is significant to build a significant amount of weight, even at 1 mil. I just don't see 5 lbs, that is all. 25 lbs may be too high as I first guessed, but I was going on my 3-mil epoxy two part primer.

As far as F-14 on the deck of a carrier, if that is what you are doing in your RV, carrier operations, you better prime it ALL! My RV lives in a hanger with dry wall and rarely flies in rain. You all know more about primer than I ever will or want to. Thanks for straightening me out.

[szicree]

I've been priming the heck out of my whole project from day one and never checked the film thickness until yesterday. I carefully mic'd the piece before and after my usual priming routine of clean, etch, alodine, tack coat of AKZO followed by medium coat of AKZO. Drum roll please....1 mil exactly! I wish to add that the coat is definitely not transparent as some have said it would be, but rather a lovely shade of baby-poo green. However, I suspect that sharpie marks would show through it. YMMV.

[az_gila]

Originally Posted by szicree

I've been priming the heck out of my whole project from day one and never checked the film thickness until yesterday. I carefully mic'd the piece before and after my usual priming routine of clean, etch, alodine, tack coat of AKZO followed by medium coat of AKZO. Drum roll please....1 mil exactly! I wish to add that the coat is definitely not transparent as some have said it would be, but rather a lovely shade of baby-poo green. However, I suspect that sharpie marks would show through it. YMMV.

Steve... I've been assuming that the AKZO is an easier to apply equivalent of MIL-P-23377 epoxy primer, with more suitable properties for interior protection.

It's made to a Boeing (nee McD. Doug.) specification. I'll see if I can get that spec. at work on Monday and compare it to the Mil-Spec.

The Mil spec is 0.6 to 0.9 mills, so if the AKZO is similar, you could ease off on the second coat...

On a day when I'm spraying well, I could apply it so the grain showed through.... but a little less, and bare spots appeared.... remember the primer works in conjunction with the alodine, that's why no corrosion is allowed even in the scratched areas after the salt spray test...

gil in Tucson