Folks
Another little update.
Fuselage is in white and I hope to put the red stripes on this coming weekend.
The left wing is the one that I used acetone as a final wipe before primer and then I did not wait long enough before shooting primer. The acetone finished evaporating through the primer and messed it up in a few places. So I had to sand that wing pretty hard and reprime. Then sand before final paint. So.......it looks like this......
Left wing ( with 1 aileron cable, tip light mount, light wires, pitot tubing, tank straps but no tank or lid, square tip,) weighed 73.85
After all fabric, stitching, tapes etc - 79.4
After 1.5 coats primer - 85.25
After sanding the primer on all of the top and about 10% of the bottom - 84.2
After top and part of bottom re-primed - 85.7
After sanding again - 85.05
After final paint (white with red LE) - 88.15
So what does all this mean? Once again I will state that you can sand a lot but it will not take all that much weight off. In this case I sanded very aggressively (can see the fabric in lots of places ie the primer is mostly sanded off) and it took off maybe 15% of the weight. So fabric (inc glue, stitching, tapes,) added about 5.5 pounds. This value is not dependent on system used. They all use basically the same fabric, tapes, stitching etc. Then the primer added about 5.8 pounds. I sanded off about a pounds worth then added back a pound and a half on the reprime, then took a half pound off sanding a second time. Then I shot about three cups of white final color coat and yes sports fans, it added about 3 pounds reiterating once again, a quart paint cup adds about a pound. Final wing weight came in at 88.15 pounds.
So fabric adds about 5.5 pounds
Primer and paint add about 9 pounds for a total of roughly 15 pounds for fabric and paint on a square tip Cub wing. Folks I am putting this stuff on about as thin as possible.
One Cross coat, plus 1 pass for 1.5 coats of primer, sanded to fabric, followed by one cross coat color.....looks like this in primer.....
The tiger stripes is where the primer is sanded so thin you can clearly see the fabric, the white top coat completely covers this, so it does not hurt to sand it thin. The airplane will not be tied down outside year round so I am not worried about UV issues from sanding the primer too thin.
It can be tough to see in the photos, so here is another shot....
And again........part of the reason for the sanding is to get a nice smooth surface to put the topcoat on and also to try to keep the paint as thin as possible to improve flexibility and durability. The objective is to get the very best possible finish with the minimum paint thickness and the least weight.
The right wing primer came out better as I used alcohol as a final wipe and gave it plenty of time to evaporate. So we shot primer, sanded the primer, and painted the white topcoat. Unfortunately I did not do a very good of shooting the topcoat (lots of orange peel on the bottom, then once again I did not wait long enough after the final wipe and it pin holed the LE red stripe pretty bad - Doh - you would think I would learn). In a nut shell I was not happy with my workmanship. So we (MMR came over and helped) started sanding down the red stripe and the bottom of the right wing (the top came out OK) and I will repaint the bottom and red stripe.
Right wing before cover (as above) - 73.2
After covering - 78.9
After primer - 83.8
After sanding - 83.1
After paint - 85.8
I will weigh after color sanding the bottom and the red stripe on the LE, then again after final paint.
Once again the stripes are where I have sanded the paint all the way down to primer. Trying to keep it thin. I expect to be able to re-coat the bottom here in basically one pass (so half a cross coat).
Lessons learned so far
1) use the system products all the way. If they have a reducer use that - don't substitute acetone, Lacquer thinner, or MEK
2) if they have a final wipe product - use it. Don't substitute alcohol even if their product smells just like it. Perhaps one of the reasons my final wipe with alcohol did not flash off quickly is that it was 91% alcohol and 9% water. Air-Tech final wash smells like alcohol but that last 9% might be acetone, or some other chemical. My thought is that the alcohol flashed off just fine but that last 9% water may have left almost microscopic water drops that did not have time to evaporate before I sprayed. At any rate what I am now doing is cleaning, final wipe with Air-Tech products, in the evening and spraying the next day. Giving it 8 to 10 hours to flash off. Excessive? Yes but I am tired of sanding so I don't want to take ANY chances. Those items I have sprayed after a long flash off have all come out pretty good. At this point I am happy with the tail feathers, left wing, and fuselage. The right wing will be good after a respray this weekend. Because of all the sanding I am not concerned about paint or primer build up for the two areas I have had to redo, one in primer and one in paint. I think it would be pretty easy to get a good finish if you did not worry about how much primer and paint you put on. It is much more challenging to get a really nice finish with minimum materials, and it takes a lot more time. Is it worth it? Beats me, that gets down to what your standards are and what is acceptable to you. Another aspect to that philosophy is the exponential curve issue. An average job takes 50 hours, a better job takes 100 hours and the best job takes 1000 hours. I don't really have an answer there. Furthermore, I might strive for that "best" job, invest a ton of time, and still come out with an average job. If and when I do this again it might be fun to try to crank out a Cub in record time and see what it comes out like, and not worry so much about every single speck of dirt in the paint, or use plywood for the floors instead of spending lots of time and money on composite floor boards. Things like that.
3) Extra reducer in the primer helped. Extra reducer in the paint equals runs.
4) You must replace the plastic floor and clean the booth thoroughly before each spray session. It is amazing how much dirt floats around. I am still fighting this issue.
5) Don't leave the masking tape on more than a couple of days. It will leave residue and gets much harder to remove after just a few days. I will do a post on taping this weekend.
6) While waiting the 20 to 30 minutes between the first pass and the second pass of the cross coat, I clean the gun and start with a fresh batch (cup) of paint. On my last build I had a couple of really bad spray experiences that I attribute to the paint starting to set up in the cup and also drying in the gun nozzle while waiting between coats. So now after the first pass, while waiting for it to tack up, I throw out the left over paint in the cup, clean the gun, and effectively start over. I mix a new batch (cup) of paint when ready to spray again. It has worked well so far in that I have not had the disasters I had the last time. The last Cub I built was a flying paint train wreck. I am still not all that good with all this paint stuff but feel I am at least getting better. Hopefully you can learn something from my mistakes, and when you get to see my Cub at gatherings you be able to look at the finish and see some of the things I have written about, and learn a little more.
7) Everyone says painting is all in the prep. Bunk. I can invest 50 hours and have awesome prep, and then I can ruin it all in 10 minutes in the paint booth. Painting is a perishable skill. About the time you get it all figured out and get pretty good at it you are done and don't do it again for several years, then you have to learn it all over again.
8) Painting takes help. You will need friends to help move parts in and out of the booth, flip wings over for sanding, etc. A lot of the build can be done solo but I find myself needing help more in this phase than any other. Many Many thanks to MMR, Cal, Glenn, Ken, Buck, Lytle, Jim and others for helping me weigh wings, fuselages, turn things over, sand, put plastic down, etc etc.
Hope all this helps
Bill