Has anyone done an actual semi-scientific rattle can primer comparison?

My situation: I'm about done with the tail, and I've been using Dupli-color self-etch throughout, mainly for reasons of simplicity. (no paintgun setup/cleanup, and the ability to run to Advance when I need a restock)

However, I've been kind of underwhelmed by the stuff. Coverage doesn't seem that great, and the durability is nothing to write home about. Frequently I find myself scratching the primer during assembly and then going back and touching up afterwards.

Anyways, now I'm about to have some downtime between wrapping up the tail and waiting for my wings to arrive in March, so I was thinking of picking up cans of NAPA 7220, Sherwin GP988, and SEM, and doing some side-by-side comparisons. Same prep, same application, same cure time, then subject the primed pieces to some scratch tests and so forth.

I figure it'll be educational for me and also useful for future builders who want to do rattle can but want some better comparison data than what usually comes out of searching the forums here. I never found a good comparison like this, just a lot of "I used XYZ and it was great/OK/horrible etc." Not to say that those aren't valid data points, but it's a lot harder to parse them into a real decision IMO.

Thoughts?

I used both napa 7220 and duplicolor. I found them both to be about the same. Neither held up well to scratches or acetone or mek. Akzo epoxy primer is significantly better than the rattle cans.

I used 7220 on my 9A, and I'm using AKZO on my 10. The 7220 was nice for doing small batches and did not require prepping/cleaning a spray gun. The downsides were it scuffed easily, wiped off with solvents, and seemed to absorb oily finger smudges. The AKZO takes extra prep time and requires mixing, but the durability seems to be much higher. I don't plan on using the 7220 on my 10. So far I'm getting good results with the $12 purple spray gun from Harbor Freight.

SEM

Went to a pro auto body shop. Been using
SEM self etch primer large cans. Works very
Well. Drys fast and does not scuff off easily.
Would use it again. I prep the surface with a scotch
bright pad. Clean with Big Sky degreaser/ cleaner.
The big sky was also sold in the auto body supply.
I also use a 2 part DuPont epoxy primer ( mixed to the same
Color as the SEM) for steel parts and high wear areas.

Picked up a can of 7220 on the way home from work today. Tried to go to the Sherwin Williams store for 988 and SEM, but they were closed...I'll have to run by on the way in tomorrow morning.

Obviously none of these options are going to compare to a two-part epoxy like AKZO, I'm not debating that at all. But I would like to put together a good objective comparison of the rattle can options, both for my benefit and for other builders who are leaning towards rattle can but not sure what to get.

My personal experience is that the Duplicolor is plenty tough IF you let it cure at room temperature (~70F) for a few days. To save my fingers and scotchbrite, I prime before dimpling. As long as I wait a couple of days, the primer holds up to dimpling just fine. The photo below shows one of my wing walk doublers that was dimpled a few days after priming.

I'm very interested to see the results. I've gone about as far as I can with all the empennage pieces (HS, VS, rudder, elevators) before having to prime. I used the Dupli-Color self etch on the practice kit. Like you, I wasn't particularly impressed.
Unfortunately, it's proving very difficult for me to find decent priming weather in the winter. Fortunately, that means I haven't shot any primer on the empennage parts yet, so I'm still wide open to options. Like I said, interested in seeing the results... Thanks for doing this.

PS- More bad news... The SEM self-etch is $30+ locally

I used the sherwin Williams but tried a few others along the way. I was not happy with any of them for scratching off. The longer the cured the better they did but not good. I was told that Duplicolor is made by sherwin Williams just a different color. While working on the fuse I decided to try alodine before prime. What a difference. I have started alodining all the parts. Isn't that hard to do and really helps the primer grip. I recommend etch and Alodine and then any primer. I did still use the self etch primer after the alodine even though they say it is not necessary. It worked better.

I've used SEM exclusively on the fuselage and have been generally pleased with the results. What kills me is the cost of the stuff. I initially paid $10 a can for it back in 2006, (yeah it's a slow build) and have had to pay as much as $23. Yesterday I found it on sale at ToolTopia.com for $13 with free shipping on orders over $100. I ordered just enough to finish up.

I have used some of the rattle can stuff when I don't feel like having to mix us some of th AKZO. The durability of the ones that I have used is just not that great. Some of those parts I removed the primer and reshot with AKZO.
AKZO is really durable and it shoots pretty easily once you learn how to use a spray gun. I wouldn't say cleaning the gun is that big of a deal. The biggest issue I have with it is you have to wait 30 minutes after its mixed before you can shoot it. This is really annoying if you didn't mix up enough paint to complete the batch that you are shooting. All in all though its a great primer.

I have to put a good word in here for Stewart Systems Eko-Prime.

The guy who started my -7A was using it to prime everything, and I got about 3 quarts when I picked up the kit. So far I have been quite impressed with it. It's water based. No solvent fumes, everything cleans up with water, and you can thin it with distilled water as well.

I didn't think it would be very tough, but I'm here to tell you it's a whole lot tougher than the rattle-can self etch primer I tried. It dries pretty quickly and pretty hard, and the parts that were primed a while ago (before I got it) show that the primer holds up quite well. I can see bucking bar scuffs, but not scratches from incidental contact like I see with the rattle can primer. It may not be as tough as AKZO (I haven't tried it to see), but I spent over an hour in my garage the other night priming wing ribs. It was below freezing outside, kerosene heater was going, 56 degrees inside, no open doors or windows, no mask, no respirator, SCUBA tanks or hazmat suit. When this gallon is gone I'll probably buy more.

Oh -- and I also loaded up the Paasche airbrush when I needed to just spray a little bit. What you don't spray can go right back in the can.

Rattle Can

N546RV said:

Anyways, now I'm about to have some downtime between wrapping up the tail and waiting for my wings to arrive in March, so I was thinking of picking up cans of NAPA 7220, Sherwin GP988, and SEM, and doing some side-by-side comparisons. Same prep, same application, same cure time, then subject the primed pieces to some scratch tests and so forth

Click to expand...

In the picture below, you can see the green Duplicolor on flap bracket, darker grey Napa 7220 on ribs, and lighter grey SEM on aft spar. I didn't try the SW because it's almost as expensive as the SEM and harder to come by for me. I didn't do a formal comparison study per se but the main thing I took away from using all 3 was how much smoother and better the SEM covered. I chose to use SEM because of that.

A real build up 2k primer sprayed from a gun has a lot more fill capability than any rattle can, however it's heavier. I haven't built an Rv so I can't say what you should use, but i would certainly use it on the fiberglass surfaces.

Update: So I finally have gotten around to doing this. Tonight the experiment has begun.

I gathered a can each of Duplicolor, 7220, and SEM. I wanted to try the SW and maybe Mar-Hyde, but I haven't had any luck finding any of those locally, and the Mar-Hyde at least was pretty expensive online...like $16 a can. I did score a can of SEM off Amazon for $9. (not including shipping)

First impressions: Both the 7220 and the SEM go on much smoother than the Duplicolor. Like one or two passes with either of those, and I feel like I have good coverage. The Duplicolor, on the other hand, seems to come out in a more "spotty" pattern, and it takes 3-4 passes or more before I feel like I've got good coverage. (this has been my experience throughout my empennage using the Duplicolor as well)

So so far, I'm much more impressed with the 7220 and SEM. Once the samples cure, I'll do some testing to see how durable each primer is. Look for a full report in a few days.

Philip,
I'm semi-interested in your test results, but I think you should consider cost and availability with the mission. You are talking about priming parts that, after construction, will never see any abuse or the light of day, most likely. If it is in an area that might see wear, maybe another more durable coating should be considered. If you scratch something during construction/assembly that causes concern, just shooting it with a rattle can is not much of an issue. The only true test with these considerations is how it holds up long term in the interior areas we deal with. I don't think you can test for that without some really expensive equipment. Any self-etching rattle can primer is probably better that nothing on alloy parts, and useless on unscratched alclad parts.

Scott Hersha said:

Philip,
I'm semi-interested in your test results, but I think you should consider cost and availability with the mission. You are talking about priming parts that, after construction, will never see any abuse or the light of day, most likely. If it is in an area that might see wear, maybe another more durable coating should be considered. If you scratch something during construction/assembly that causes concern, just shooting it with a rattle can is not much of an issue. The only true test with these considerations is how it holds up long term in the interior areas we deal with. I don't think you can test for that without some really expensive equipment. Any self-etching rattle can primer is probably better that nothing on alloy parts, and useless on unscratched alclad parts.

Click to expand...

Honestly, I'm as concerned with efficiency as anything else with these "tests." I went with the Duplicolor for the empennage because I read good reviews of it here, but I haven't been very satisfied with it. For one thing, I find that it scrapes off very easily, just from doing normal stuff like bucking rivets and so forth. It's a pretty trivial matter to touch up any scratches, but the inefficiency of that bugs me...priming, then priming again. I also went through what I'd consider to be an unseemly amount of Duplicolor for the empennage, and I think that has a lot to do with how the stuff sprays, and me needing to make a lot of passes with it to get good coverage.

So my reason for doing this comparison is to find out if there are better rattle-can options out there than Duplicolor. In retrospect, the way I picked Duplicolor for the empennage was not much better than just taking a shot in the dark and picking a random primer, and I wouldn't expect to be much more successful if I just went and started using another rattle-can primer.

When you get down to it, most of the opinions here tend to take the form of "Well, I used [Duplicolor|SEM|7220|Sherwin|somethingelseentirely] and it worked great for me." That's useful information, but it doesn't really say anything about how the different options compare, and that's what I'm trying to find out.

I'm under no illusions that I'm conducting a study that will be submitted for peer review. I just want to see for myself - and also provide for future readers here - how these options stack up side-by-side. I'm quite likely overthinking the primer issue quite a bit, but what the heck...it's fun for me, and maybe helpful for others.

Personally, the SEM would have to significantly outperform the other two options for me to go with it. I don't know of anywhere local to buy it, and while the price online isn't horribly more than the other two, the simple inconvenience of having to wait for a delivery vs. running around the corner to Advance or Napa is a big factor for me.

N546RV said:

Personally, the SEM would have to significantly outperform the other two options for me to go with it. I don't know of anywhere local to buy it, and while the price online isn't horribly more than the other two, the simple inconvenience of having to wait for a delivery vs. running around the corner to Advance or Napa is a big factor for me.

Click to expand...

I use SEM to paint the kydex interior panels in my RV-10. I found it at both the SW and PPG distributors that service the local autobody shops. They tend not to stock all colors across the various product line, but the SW distributor was able to get it over night, which would imply that there is a local warehouse for distribution.

As far as comparisons go, I used SW rattle can selfs etch primer on the first two airplanes. On this one I've used SW and also Rustoleum self etch primer made for bare metal/aluminum. They are both very similar in terms of durability. Both will scratch off under certain circumstances. The SW is gray, as you know. The Rustoleum is green. Coverage with the Rustoleum can seems to be a little better. I can buy the SW locally for about $9 per can. The Rustoleum is about $5.50 at Lowes. I'm only priming the non-alclad parts, so the price difference isn't a huge deterrent.

I have used the duplicolor products for a long time on a lot project. Except for a few bad cans here and there I have been very happy with the product. I used the Duplicolor self-etch on my RV. The trick with the duplicolor is to cure with a little heat. I use my propane torch (with air bleed off) to warm the part so it is maybe ~120*F. I do this after the primer has flashed off or before and after if it is cold out (only warm to 80-90* before). With a quick heat cure that stuff is tough as nails. You cannot scratch it with a fingernail. Heck, I was back-drilling a part and the chuck of my drill touched the skin. It barely scuffed the primer.

For the interior paint I scuffed the duplicolor primer and put on a coat of PPG MTK Epoxy Primer. I had no adhesion or reaction issues at all.

Acetone will take off the diplicolor no matter how long it has cured. Handy at time when you mess up a part and want to re-prime, just wipe it off.

Some of these primers are just that - primers, with little to no corrosion protection beyond being a barrier film. Because of that, they need to be intact to prevent corrosion.

There are self-etching corrosion-protective primers such as zinc chromate available in the rattle cans. These actually help prevent corrosion.

Dave

I see two uses of primer.

One, to prepare the metal or fiberglass for the final top coat of paint. This would be typical of visible surfaces. Sealing, corrosion prevention, etc. are not important for this use because the top coat(s) of paint provide protection.

Second, to protect the metal or fiberglass from the environment, wear, and corrosion. This might be used on interior where appearance doesn't matter. An Alclad surface would offer good corrosion protection, though maybe not for physical wear, and all cut edges would not enjoy the Alclad layer.

Seems to me that a primer that's good for use #1 might not work for use #2, and vice-versa. For instance, somewhere I got the notion that the acid-etch primers are great for preparing the surface for top coats, but don't provide protection against corrosion.

Comments?

Around my hangar, I've stopped using 7220 and now use the Rustoleum Self-Etching Primer. Feels more durable, and I like the way it goes on...works great IMO, and available everywhere for cheap.

"Etches and primes in one easy step"

Priming using different AKZO products

Hello everyone,

I am about to start a -10 build. My tail came last week and I am finishing the shop. The "engineer" in me still has not made a decision on what primer to use, but I will be priming. I searched the web for information and came upon a few links that actually describe a testing method and results for different priming methods/products. The emphasis was on removing Chromates and making the process healthier and more eco-friendly. AKZO did the study. I wrote to the AKZO person who presented the paper and he said AKZO's recommendation for chromate free aircraft internal priming is to use 2100P003.

Here are the links to the papers. The links look the same but they actually point to two different papers with similar material. I am neither endorsing or recommending anything except educating ourselves on what is available.

http://www.nstcenter.biz/docs/PDFs/MR2010/Wednesday-3-Presentations/3-Brown_Adams.pdf

http://www.lockheedmartin.com/conte...obel-Chromate_Free_Coatings-Patrick_Adams.pdf

I will be starting with building some outdoor lamps using Aluminum while I master my sheet metal skills. I will probably order a sample kit of each of the Akzo products and try them, assuming they come in sample kits smaller than gallans.

Regards,

Michael

If allowed to cure long enough the rattle can primers (lacquer based) become very durable and can't be removed easily even with lacquer thinner, acetone or even MEK. I had a patch of the zinc chromate rattle can primer on the fuselage my RV-7A that was a couple years old and when the airplane was painted we could not remove it - we ended up scuffing it and then painting over it. I was amazed it was that tough!

When it is fresh solvents remove it ASAP.

Azko vs Steward

My only non-scientific empirical observations are on ASKO nobel (from ACS) and Stewart systems. The Azko is tough as nails. Really hard to scratch, immune to just about every solvent I have tried. The downside is it is fairly toxic. I used a fresh air respirator to apply it. Did the entire internal airframe with it and don't expect to see any corrosion.

I used the Stewart Eko prime under areas that I was painting--also with Stewart Systems. They are really nice people to work with and very helpful.
EKO prime works great under the top coat. It is also fairly tough but can be removed any time with MEK and probably a lot of other solvents. It would probably be okay where you are not going to see any movement but don't rely on it anywhere there might be abrasion or any solvents.

My $02.

Michael Wynn
RV 8 Finishing
San Ramon, CA

Buggsy2 said:

I see two uses of primer.

One, to prepare the metal or fiberglass for the final top coat of paint. This would be typical of visible surfaces. Sealing, corrosion prevention, etc. are not important for this use because the top coat(s) of paint provide protection.

Second, to protect the metal or fiberglass from the environment, wear, and corrosion. This might be used on interior where appearance doesn't matter. An Alclad surface would offer good corrosion protection, though maybe not for physical wear, and all cut edges would not enjoy the Alclad layer.

Seems to me that a primer that's good for use #1 might not work for use #2, and vice-versa. For instance, somewhere I got the notion that the acid-etch primers are great for preparing the surface for top coats, but don't provide protection against corrosion.

Comments?

Click to expand...

On the exterior surface filiform corrosion is expected. The top coat, usually polyurethane, is the reason for filiform corrosion. To prevent it a primer is needed.

Traditionally only alodine-primer-top coat would give good protection, but today good primers are formulated without the use of chromates. They give excellent protection against filiform corrosion. The catch is, that is the only thing they are good for (in addition to adhesion of course). It is better to think of primer and top coat as one singe product, used alone they are no good. Following the manufacturers procedures is essential. Typically such a primer needs to be covered by the top coat within hours. Used alone, many primers are porous and will accelerate corrosion because they collect moisture.

Other primers, such as chromated epoxy primers made for aviation applications, are used for internal surfaces. You cannot go wrong with a chromated epoxy primer on the internals. They are strong, durable, and waterproof. When using an "aviation grade" primer, they cover in a very thin layer. The only thing I can think of is it's like shooting small birds with cannons. What Vans are using on the internals on the QBs is probably more adequate for the job, but I don't think it is any easier to apply than an epoxy primer, so why bother?

For the internals, crevice corrosion is the only thing to think about. This corrosion typically occurs between mating surfaces. Chromated epoxy on everything is the brute force method. What is needed is merely a coating between the mating surfaces, but again, it's easier to just cover everything when you're at it, looks much nicer too.

For the internals, it is important that the primer do not create an environment for filiform corrosion. It is important that it is not porous, but repels water. It should be physically and chemically strong. Chromated epoxy is made for this. On the outside, it is much more important that the primer(s) and top coat(s) are applied according to manufacturer's spec.

But then again if you live and fly in a dry climate far from the coast (salt water), store it in a dry hangar, your airplane (or yourself) will become old and useless long before corrosion takes it, even "unprimed". Living and flying near the coast is a totally different matter.

A common misconception about alclad is it doesn't protect at edges and scratches. The corrosion protection mechanism of alclad is galvanic protection. The pure Al or AlZn alloy of the clad is a sacrificial anode to the AlCu alloy of the core. At edges and scratches the clad will corrode, while the core will not. The clad work exactly like sacrificial Zn anodes used in boats.

I am also looking into rattle cans, because it is faster. So far the only solution I have found is one particular that applies in a very thin layer, and then is covered with a thin transparent top coat to repel water and create some physical strength. That is a two step process, and seems a bit silly, but it works. But is it faster than using two component aviation grade epoxy? Another one is a rattle can primer for marine application (aluminium boats and engines, propellers etc). That one has pure aluminium pigments, thus it works just like alclad (galvanic protection). However it is a total mess to apply in anything but a thick heavy layer, so it is useless.