filling rivets for painting

I have had the chance to look at several RV's in the past month, and they have been very nice. From paint to panels, I was impressed. My only previous experience building was with a glassair and a kitfox. One thing I liked about the glassair was how smooth it was. I am building a -9, so they are flush rivets.

I have about finished my empannage kit and there are a few places I will need to fix from the rivet gun getting away from me. I am comfortable with epoxy and fillers, but only have experience with fiberglass or wood boats. I would like a smooth finish with the rivets invisible.

I searched the site and got lots of painting advice and how to do the fiberglass tips, but not much on covering the rivets to a smooth finish. I have a few questions I would sure like opinions about.

1. should I prime the aluminum first of fix the marks and cover the rivets first?
2. I have read many opinions on what to use - epoxy or Evercoat type product. My experience is with West Systems and believe it would be the strongest and have the best chance of holding the rivets solid and not flexing through the finish. No matter how tight a rivet, it may move from flex or heat - cold. Is this a concern that I need to consider?
3. Has anyone else done this and can you give me advice and pictures?

Thanks for the information and help.

It's a metal airplane there are supposed to be rivets. Too much work and weight to fill every rivet.

my plane

I understand metal planes have rivets. I also know it is my plane and I can finish it how I want to finish it. Im not looking for opinions on if I should or should not fill the rivets, but what way is the best to do it.

As for the weight, there is no way it will add more than a pound or two to the plane if I filled every skin rivet. I could skip lunch and it would be equal.
I have filled screw holes on boats and worked on a glassair and know how much material is used. There will be much less filler weight than primer weight.

I just tried a couple rows on the VS with west system and micro balloons. I sanded the area with a 120g sanding pad to roughen it up and cleaned with lacquer thinner. I used a hotel card key to skim over the row of rivets. I will wait until tomorrow to sand and check out how well it worked.

That is an interesting concept, good luck with it. I don't think I have ever heard of someone doing that.

thanks Don

Thanks Don. I love looking at your weblog and pictures. I can't wait to see your RV 12 with the FIT engine in it ready to fly. Nice prop!

I may not skim all the rivets, but I saw a HS and elevators done on a -7 a couple weeks ago and it looked great. I am aware of too much filler and flutter issues, and looks are not as important as safety, but why not give it a shot!

I've seen more than a few RV's with this done, although it was primarily on the wings. The only issue I know of is that certain areas begin to crack due to the vibration around the rivet. If it were me, I would probably toy with the idea of using fuel tank dimple dies where possible on the plane. It would allow for a little more depth. Just a suggestion.

great idea

danielhv said:

I've seen more than a few RV's with this done, although it was primarily on the wings. The only issue I know of is that certain areas begin to crack due to the vibration around the rivet. If it were me, I would probably toy with the idea of using fuel tank dimple dies where possible on the plane. It would allow for a little more depth. Just a suggestion.

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That is a great idea. I will give that a try on some scrap and see how it works. From the test spots I did on scrap, the epoxy holds on like crazy and sands to an invisible edge. There is a pinhole problem with epoxy, but that will be managed with primer and Evercoat. My neighbor owns a body shop and said he would spray any test pieces I want when they are painting at the shop. That should give me a good idea on how well it is working.

I thought of trying it on my test toolbox kit, but it turned out so bad, I am embarrassed to show it to him!

Check this out

Rockwood - check out this page

http://www.aircraftspruce.com/menus/cm/fillers.html

The only reason I would see not to do it is that if you have to repair something someday you'll have A LOT more to do than just drill out some rivets.

Av8torTom said:

The only reason I would see not to do it is that if you have to repair something someday you'll have A LOT more to do than just drill out some rivets.

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This too! I've also seen some that they put strips of fiberglass over the rivet lines, and feathered them out. But again - repairs would be 10x more difficult to blend beyond recognition.

lots of fillers and epoxy

Thanks Tom. I have used west systems pretty much exclusively building boats and on the glassair I worked on. I never even knew much about others - but this page has a bunch of info.

I saw they have Bondo. I built the full size mock up of the B-2 for the movie Broken Arrow. I used cases of Bondo to take it from a plywood skin to look like the real thing. that was an interesting project.

No Bondo

Yeah, don't use the Bondo for fill though - if you read the description it suggest uses like temporarily holding things in place etc. It's not flexible enough.

I will be using something to fill in the occasional dent or 2 I've managed to cause. Let me know if you try any, and what your results are.

T.

BTW - someone here had suggested using fuel tank sealant. Put a little dab on the rivet head and squeegee most of it off to JUST fill the rim of each rivet. Sounds like it might give a little smoother look, but not hide the rivet if repairs are needed. Tank sealant takes paint nicely too... something to consider.

I'm really interested to see how this turns out. Can you post some pictures of your lab work?

I did this to all my top rivets on my Mooney, wings,cowling etc. I painted it 8years ago and it still looks great.
I used a light coat of 3M glazing putty, sanded then applied several coats of epoxy primer and basically sanded back off except a bit around each rivet.
I got it to the point that if I got down and looked closely down the skin I could just make out the rivet line. I did this incase a repair would ever be needed.
This is how I also preped the tail and wings for my 7 . Very little weight added.

that might be the ticket

N9331v said:

I did this to all my top rivets on my Mooney, wings,cowling etc. I painted it 8years ago and it still looks great.
I used a light coat of 3M glazing putty, sanded then applied several coats of epoxy primer and basically sanded back off except a bit around each rivet.
I got it to the point that if I got down and looked closely down the skin I could just make out the rivet line. I did this incase a repair would ever be needed.
This is how I also preped the tail and wings for my 7 . Very little weight added.

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I have used the glazing putty and now that you mentioned it, it may be the best of both ideas. It is limited to very thin filling, but that is all I am looking for. For any of the small dings, I would still use some type of epoxy. The nice feature of the glazing putty is it doesnt have the pinholes. Bondo is way to heavy for aircraft unless it is VERY thin.

At least for me it has been impossible to set all the rivets on a rib or edge perfectly with no dent. The better the paint job, the easier it is to see the indententions. That is what I am looking to hide. Great idea on the glazing putty.

Filling rivets

Rockwood
I had my painter fill the rivets on my 9's wings. He didnt use bondo he sprayed the row of rivets with high build primer, then sanded it off. What was left was a very small ring of primer around the rivet. The result was visually appealing, you can tell it is metal plane but it is very smooth. You can see the occasional faint outline of a rivet here and there. I wanted to ensure the paint bridged the gap between the rivet and the skin. This method achieves this goal and from my estimations at very little extra weight but at quite a bit more labour cost. Aprox 43 hours for both sides of the wings, flaps, ailerons, and horizontal empenage. I'm not presuming that it will be any faster but it sure looks good.

Matt

has to be faster

Matt, there is no way it couldn't be faster - even if it is only in your mind! Thanks for the idea.

Primer

First, do not use any of the non catalyzed fillers. They are constantly shrinking and will react to some primers. Not good. Use Evercoat 416 for a super light filler and easy to sand.

Regarding the rivet fill, the best process I have seen was simple, quick and used only a few ounces of high build primer. Clean the rivet lines with alcohol. Lots of ways to do this. Use high pressure air to blow out the rivet line and make sure it is dry.

Mix the primer and simply finger paint primer into each rivet. This pushes primer into any of the gaps. For me this is enough and I still want the rivet lines visible. Inspect and repeat as needed.

For the smooth finish, do the above then spray primer over all the rivet lines, sand and repeat as needed.

I'm confident this can be done with only a few ounces of primer. I did this on my plane and only used about 4 ounces of primer in a couple of 2 ounce sessions. And, I didn't use all of it. I only did the top, or visible surfaces. The rivet edges were filled but still visible.

I saw a "clean" RV at Oshkosh. Very nice. However if you want it judged don't expect any awards. Big deductions for no visible rivets lines!!!

Smooth rivets

I too am aware that this is a rivetted plane, and by traditional standards, the rivets should be visible. But my girlfriend, who was my co-builder, insisted that the rivets were to be filled. She has used Super Fil, which is very light. For the complete 7A, including the cowling, 32 oz was needed, and lots of it was sanded away to make a smooth finish. I absolutely have no regrets now that the PH-OBO is done.

Av8torTom said:

BTW - someone here had suggested using fuel tank sealant. Put a little dab on the rivet head and squeegee most of it off to JUST fill the rim of each rivet. Sounds like it might give a little smoother look, but not hide the rivet if repairs are needed. Tank sealant takes paint nicely too... something to consider.

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Rod Bowers did this on his AMAZING "8". He said he skimmed pro-seal over a group of rivets and then immediately wiped the rivets clean with acetone. It left just enough to bridge the rivet edge and allow the paint to have something to stick to and not crack............ It looked really clean.

crabandy said:

It's a metal airplane there are supposed to be rivets. Too much work and weight to fill every rivet.

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Last year I wrote an article for KitPlanes on aircraft judging at OSH.

One of the things that came through loud and clear and was mentioned a few times during my interviews for the article was just that, an aluminum airplane is supposed to look like an aluminum airplane.

The judge's I spoke to felt that when the rivets are hidden they wanted to know what else was hidden. If you are trying to build a show plane, let the rivets show.

While strictly an aesthetic issue, it adds nothing to the aircraft but weight and more work.

Looks like some builders would merely like to ensure the finish paint bridges any gap between rivet head and skin. FWIW, two coats of PPG epoxy primer followed by base and clear left nothing unbridged, without any prior filling.

There were a couple of suggestions in this thread last month (including a brief discussion on whether or not it was worth it): http://www.vansairforce.com/community/showthread.php?t=85462

judging of an aluminum plane

As for an aluminim airplane looking like an aluminum airplane - you make yours look like you want and how about you let me make mine how I want?

I have no interest in having my plane judged at AV or anywhere else for that matter. The only judging I really care about will be done by my wife and I. As for adding more work and more weight, since I will be doing the work and the added weight will be less than a second coat of primer, neither of those issues are concerns for me.

Dan is the expert as far as fiberglass and finish and thanks for the info. I think you and RV7Guy's ideas are great for bridging the edge of the rivet to the skin. When I look at the top side of wings, no matter how great you are at riveting, the rivet line has dimples. It is more noticeable with a shinny paint job. That is what I want to go away. Just a quick skim over the rivet line with a mixture of epoxy or glazing filler, sand, prime, then paint.

Vickruis did their entire -7 and only used 32oz - then probably sanded at least 50% of that off. Weight is not an issue. The photo looks great - to me and my wife and I are that matters. I will take some photos as I try the different methods.

Thanks to those who have offered ideas on different ways to make my wings smoother. I appreciate your time and ideas.

I apologize, just expressing my opinion.

If I could do it over again, I would defer all of the extra beauty work and off plans additions until after I was flying. A baggage floor toolbox here, aluminum canopy trim strips there, hidden hinge cowl covers etc...7 years later I am still 1 1/2 - 2 years out from flying. I'm now in the simplify to fly mode.

I know some modifications are best done as you are building, but you can easily fill the rivets after flying.

crabandy said:

I know some modifications are best done as you are building, but you can easily fill the rivets after flying.

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You might want to get advise from painters on this. Once flying, some areas may get oil in the rivets. That may be difficult to clean to have fillers bond properly.

If you want a real exercise in wasted time, try filling all the pop rivets on an RV12! Yes, it can be done and has been done, I intend to do it on mine. Remember, there are 12,500 of them suckers, and a syringe to vaccinate horses is what you use to fill all them holes.

no apology necessary

crabandy said:

I apologize, just expressing my opinion.

If I could do it over again, I would defer all of the extra beauty work and off plans additions until after I was flying. A baggage floor toolbox here, aluminum canopy trim strips there, hidden hinge cowl covers etc...7 years later I am still 1 1/2 - 2 years out from flying. I'm now in the simplify to fly mode.

I know some modifications are best done as you are building, but you can easily fill the rivets after flying.

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Sometimes posts don't read the same as they are thought to mean when written. I have no issue with other opinions and enjoy reading them - and considering them. On a quickly written post, it is easy to miss the emotion intended - at least it is by me. Thanks for taking the time to let me know your thoughts.

I agree with you about getting into the air as quickly as I can. Im not getting any younger! You are ahead of me and I value your thoughts on getting the plane done.

In my project, I really enjoy the fiberglassing and finish of the plane. I am pretty good at it - not as good at keeping the rivet gun exactly right and even when the rivet is perfectly driven as designed, there are still indentations along the rivet line. I prefer the smooth look and I don't care about seeing the rivets or not - I just want it smooth when the sun shines on it. I guess that comes from boat building.

I tried epoxy last night and after looking at it today, that is NOT the way to go! I will try some glazing putty today if I get some time and I think that is the best option. Im not looking for perfection, but I know the "look" I am going for.

Filling

Rockwood,

I too am building a 9. There were several places on the 9 empennage that I think are not so aesthetically pleasing. One is the rudder trailing edge rivets another is the trailing edge of the elevators. I filled the rivet line on the rudder and the top of the elevator (building a tail dragger so I didn’t fill the underside) with Evercoat. As you said, I didn’t use much so I don’t think I added but maybe a few ounces. I hope a good cost of paint will hide most of the other rivets on the plane.

Disclaimer: My machine is not flying so I can comment on the endurance of the Evercoat.

Good luck,

I am not sure there are enough "filled" airplanes in the fleet to get an idea of what system may or may not be a lasting one. All I can add is my own observations.
I have seen only a few machines with filled rivet lines. None that I saw where executed well and most had some cracking.
I am not saying you should give up on the idea unless you can't find someone with enough hours, and years, on the airplane to make a good judgement. Not sure that airplane exists.
It is good that you are not taking this lightly and trying to gain as much experience and knowledge as possible. (before you ruin your airplane, oops, I mean, pursue your dream!) Sorry

rockwoodrv9 said:

judging of an aluminum plane
As for an aluminim airplane looking like an aluminum airplane - you make yours look like you want and how about you let me make mine how I want?...

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That is exactly why we build our airplanes to fit our likes.

What I was trying to point out with my judging comment is that some people are building planes to be judged. If I didn?t make that comment and later on someone read this thread thinking that filling the rivets would help them with the judges, when in fact, it would penalize them. And for I know, you might be trying to build an award winner, which you have very clearly pointed out is not the case.

Thanks Bill

Until I read your post, I had no idea covering the rivets would be deduction if being judged. Truthfully, I had never even thought about having my plane judged at all. I didn't know it was an option!

Thinking it through now, I can understand why the judges would want to see the rivets. I sort of feel I would have a better chance with the judges if I did cover them up!

Like I said in an earlier post, I think my wording could have been better and it reads much nastier than I intended. I do appreciate the info here and being able to run ideas past people that really do know what they are talking about.

I am just getting started and know that I don't know enough to even know how little I really do know about most parts of aircraft construction. I have been around building all my life and have built several very nice boats - from canoe's to sailboats and restored a Chris- Craft runabout. I know fiberglassing and finishing and enjoy making the finish look like glass. Im going to give it a go on the rudder, VS, and HS and see how it comes out. It may not look good and I will have to sand it off or replace the parts, but waiting for my wing kit, I have some time. I will post some pictures either way - good or bad.

And Bill, I do appreciate your posts on my questions and others. Thanks.

In regards to your quest, I did the following on all of my fiberglass pieces that had rivets. I coated each rivet in epoxy mixed with micro prior to inserting it, then set the rivet. I skim coated the entire fiberglass piece to fill the pits, and then used stranded reinforced body filler to hide the indentations caused by the rivets. After sanding with 120 grit dry paper and then 320 wet, I sealed with epoxy primer followed by a filler primer block sanded again using a guide spray. I have to say it looks good, only time will tell if I eventually see and evidence if cracking.
Where the fiberglass on the 10 meets the metal, I scuffed up with 120 and bonded the joints with 3 ounce glass tape following by strand reinforced filler, then epoxy prime and fill prime, then block sand.
The joints look great and I am hoping that the glass tape prevents any cracking at the seams.
I thought about doing what younhave proposed, but ran out of energy!

good info

Bill.Peyton,
That sounds like you have it covered. I was looking at one plane that did the same thing on the HS tips and it turned out great. My thought was if it cracked, it was the perfect place for a pinstripe painted aqround the tip!

Thanks for letting me know how you did it. It sounds like it will work great.

Cover 'em up

As you very, very clearly indicated...it's your plane and you can do what you want with your rivets.

For others that are reading this thread......I see a few posts/replies about judging. From someone who has won a few awards including 'the big ones', and from my Oshkosh Judges perspective......I can promise you that I want to see your rivets.....all of them. If you putty/fill/bondo/prime/glass/glaze/etc over your rivets it leaves me to believe that you did a poor job of riveting and you are covering up your smilies and your 'innie/outie' bucking errors. It also hides any 'working rivets' which can lead to structrual issues that you are no longer able to witness, this could be a safety issue. I've seen magnificent and beautifully finished metal airplanes that didn't make the cut at Osh due to covered rivets on any surface of the airplane. Most folks are proud of their rivets and want to show them off. Then there are a few like yourself that want them covered up. To each their own.

Good luck with your airplane building, have fun and enjoy the ride.

rockwoodrv9 said:

Until I read your post, I had no idea covering the rivets would be deduction if being judged. Truthfully, I had never even thought about having my plane judged at all. I didn't know it was an option!

Thinking it through now, I can understand why the judges would want to see the rivets. I sort of feel I would have a better chance with the judges if I did cover them up!

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Etch primer issues

To kick off an old thread, I have an issue I need some pointers with.
I am using a Wattyl (Valspar) paint process for the exterior of my aircraft consisting of cleaning, scotchbriting, cleaning again, then etch primer (Wattyl Super Etch) and finally top coating using polyurethane (Colourthane C-Series).
I originally picked this process as I can (A) get the product locally (very important as shipping hazmat to Tasmania takes forever) and (B) I wanted to so keep paint weight to a minimum as I'm building a -7 which are notoriously tail heavy with the parallel valve 360, and (C) like the look of rivets so didn't care for high build primers.
After successfully completing the priming yesterday, I spoke with a friend of mine who is a composites engineer, and he asked what I was going to do in order to bridge the from the rivet factory head circumference to the skin surface so moisture couldn't creep under the rivet head and subsequently cause corrosion. Sure enough, looking closely at the rivets, there is no bridging from the tip of the rivet to the surrounding skin by the primer because it is such a thin layer, and when I look at some interior parts where I have already top coated with PU and sure enough even these are not bridged. Having this gap with no sealing under the rivets basically negates the point of painting. His father had built an -8, but had alodined and used a high build primer before topcoating, so he could trowel on some additional high build primer mixed with micro, then sanded smooth.
So I tried filling some rivets today, with limited success. Basically the solvent in the high build primer I mixed with baloons (West 410) ended up dissolving the etch primer. After researching this further, auto body guys say never put any type of filler over etch primer (but can't explain why). I then just tried dabbing etch primer onto each rivet. Because there is so much solvent in etch primer (10% solids) it took 3 dabs on each rivet, allowing an hour between applications, before the gap was bridged, and I plan to lightly sand any high spots tomorrow (I'm hoping this etch buildup will sand). You can still clearly see the outline of the rivet, but now no longer see a lip under the rivet head. I'd post a photo, by my success with photo posting is about on par with my paint success (my fisheye story I'll save for a later chapter).
Thus, I guess what I'm seeking guidance for at this stage is:
Does anyone know of a more effective method for bridging the gap under rivets when using etch primer?
Is there any potential downside (apart from a huge chunk of time) of dabbing etch primer onto each rivet to bridge the gap?
Whilst I'm asking questions, how are people sealing to stop the moisture seeping under the overlapping skin joints (I have fay sealed/wet riveted the lower half of the fuselage, but not the top skins, however all my faying surfaces are fully primed)?
I guess Wattyl Paints never anticipated the use of a bunch of rivets on aluminium surfaces when they recommended this paint system combination, and I should have forseen this issue, but I guess this is all part of the education.
Here are some links to their product sheets
http://www.wattylindustrial.com.au/documents/industrial/Industrial Metal Coatings Brochure Feb14.pdf
http://www.wattylindustrial.com.au/documents/industrial/tds/metal/Super Etch.pdf
http://www.wattylindustrial.com.au/documents/industrial/tds/metal/Colourthane C Series Topcoat.pdf
Thanks.
Tom.

There's a school of thought that filling rivet holes is a bad idea because it will hide rivets that work loose. Same applies for vinyl wraps but nobody will admit it.

Ed

Interesting Ed. But what about the corrosion risk from moisture creeping under the rivet? I'm in agreement that filling rivets completely so you can't see them is not the best idea. I'm just trying to bridge the gap so that moisture can't get under the head. You can still see the rivet quite clearly, there's just no gap. I'm even thinking about leaving some etch primer out to evaporate and thus thicken so that I only have to dab around the rivet once.
Tom.

Take a look at West system G flex, this epoxy does not dry hard and brittle, this might work, I used it with cloth blending in the FG tips, no paint cracks yet, but the expert here is Dan H. maybe he will chime in.

Thanks Bret. I have some G-flex I used for the windscreen fairing so that might be worth a try, as it doesn't have the huge amount of solvent that the high build primer does. I'll test tomorrow to see its compatibility with the primer. I'll mix it with some West 410, as although it's pretty thick on its own, I it will be a dog to sand without the filler.
I too am waiting for Dan H. to chime in, but I'm a mildly frightened he might beat me with a big stick for using the etch primer. I fire insulated my belly and firewall (that titanium sure is pretty), so I'm hoping this buys me a little reprieve...
T.

I fully agree that any "covering of rivets" looks horrible. Be proud of those rivets!

I surface prep similar to you - AlumiPrep, Scotch Brite and a lot of rinsing. For exterior painting I also go over the piece with a solvent right before prime. I offer that some primers are better than others to eliminate rivet bridging. For me, I use PPG DG-40LF and never had a bridge problem. I do first apply a light coat along the rivet heads, then go over the entire surface. I painted two planes like this and am happy with the results. Note - PPG DP-40LF is an epoxy primer, not self etching. The prep I listed does the etching process - and primer goes on as soon as the piece is dry (but no more than 24 hours).

Perhaps you can experiment with whatever expoxy primer you can get locally.

Carl

Gap

Wow...nice topic...
Going to the airport now to see if my paint bridged the gap!
I did plenty of filling where the fiberglass joined the metal. Tips etc. Plus the targa strips. Also the pop rivets around the plexi that had holes in them.
Oh course I was more concerned about the top of the plane over the bottom and same for the white paint over the red. Pretty sure if the rivet moves to smoke, then it will show through the filler, but where I filled was not really places that were structural.
But still going to go look and see if I bridged the gap.......

I machined a custom 'large' mushroom set. With it and low pressure on the gun (or as needed) it set rivets fine without making a dimple. Different methods help and practice too.

Someone mentioned wiping proseal into the dimple rings; can't get much simpler than that. And it won't crack.

Judging (from earlier in the thread): it is what it is, but it's also incredibly stupid. How much filler is on (all) the plastic award winners, and what defects in workmanship are covered on those? How many past award winners are near gross weight before adding fuel? How many were built/finished/painted by Parker P-51s? Any downgrades for polyurethane on fabric? etc etc

But if little statues float your boat, at least you know what it takes to get one.

(Got the plaque; get to say it.)

Charlie

Well it's sounding like I need to find myself a normal build epoxy primer compatible with the PU topcoat I have already purchased, then just shoot a little extra down the rivet lines just to be sure that there is bridging between the rivets and the surrounding skin. I'm really not looking forward to all this surface prep over again. I'll be at the hangar shortly to see how that etch has held that I dabbed onto the individual rivet heads.
Tom.

After 6 years of flying, I still am glad we filled the gaps. We did not try to make the skin look like epoxy, just filled the ring around the rivet head. A smoking rivet would be visible whithout any problem.
Our body and wings are red, what would mean a white ring would appear after using cleaners or wax.
There is no airplane-judging in The Netherlands, other then fellow pilots, and we have received only positive comments, even from RV-builders
As for covering up poor riveting: we wanted the outside to be just as good as the inside, so no poor riveting was accepted.

So I think I have this issue resolved.
The rivets I dabbed underneath the aircraft with etch primer were not so good. The primer had done its job sealing the gap from the perimeter of the rivet to the skin, however the excess paint on the skin was a dog to sand off. I would say for every hour you spend "dabbing" rivets, you'll spend another half hour the following day sanding the rivet line to remove the excess from each dab, then 15 minutes cleaning and shooting another layer of primer along the row where you potentially broke through with the sanding. That's weeks of extra work.
Today I tried things from a different approach. I used the flap as a test case, prepping it as usual, then laying down a dust coat over the entire flap. I then got my 0.8mm touch up gun, added some neat etch without any thinners (I would normally add 30% thinners to a paint that was already only 10% solids) and adjusted the spray pattern so that it was shooting a round patch the size of a dime at a distance of two inches from the surface. I shot each rivet individually, and once complete and tacked off I then moved back a little and shot the entire row in one narrow sweep. Finally with the main 1.3mm gun, I shot a coat over the entire flap at a 30% thinner rate, blending everything together nicely. Although this method seems to work at bridging the rivet gap, using the etch without any thinners in the touchup gun caused spider webs to form. I've run into this problem before, so I think I've just got to up the thinner rate as little as possible, but just high enough to stop this spider web formation blowing around and landing on the skin surface, as the thicker the etch the better it tends to bridge this gap. Because of this, I didn't get a chance to lay down the top coat today, as I need to let this harden up so I can hit it with some 400 grit and take the top of the remaining webs (many of them dissolved with the last 30% thinner coat).
I'll head to town tomorrow and pickup a collapsible cup adapter for my touchup gun so I can shoot the rivet lines under the aircraft. I'm using the Velocity system available here in Australia, but it's the same as the Devilbiss DeKups or 3M PPS system, and makes it a breeze to shoot paint under the aircraft.
Although we are not completely over the finish line yet, and I won't know the success until the top coat is on and flying for some time, I am buoyed by the comments in the data sheet that says that this is an "epoxy resin modified" that may be used "as a primer or, when applied in mist coats, as
conventional etch medium".
Thanks for everyone's help on this one.
Tom.

I have good results by using a squeegee to apply primer to fill rivet gaps very little sanding required