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Building Tips and technical articles. => Paint and finishing => Topic started by: Miotch on May 03, 2023, 05:28:10 PM
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Bound to happen sooner or later on this build. Last bay of the top wing I so badly wanted to get some color on. First time with Polycrylic. I was amazed at it's toughness. Too amazed. I relaxed. I drifted. I sanded. Too much.
Never relax sanding silkspan.
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Trust me, in this you are not alone.. Been there a few times too many. I hope that is on the underside of the wing. D>K
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The person who said "anything worth doing is worth overdoing" never sanded a model airplane! If you claim you have never had that happen, then you haven't built much.
Ken
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I hope that is on the underside of the wing. D>K
Oh heck no. If I'm going to screw it up, I'm going to do it right !! Top of the top wing. I think I'll paint a red arrow pointing towards it.
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Moitch,
A close up appears to show a number of pin holes where what appears to be Polyspan was heat stretched out in the tip area. It also appears you used grey primer (NAPA) and were in the process of removing it in the sand out. I'm curious here about your process in hopes to improve mine.
I have just begun using Polyspan with thinned Butyrate dope to get away from the porous silk that requires many coats of clear to fill. Additionally I have been using Polycrylic on the hard surfaces with doctors paper to minimize in house odors and complaints.
I recently tested brush applying watered down Polycrylic on a sample frame with Polyspan to seal it. You are correct the PC is very hard, it tends to leave brush strokes even thinned and is not easily sanded unless you go into a coarse grit 320 or lower which is risky on the rib edges as you have experienced.
From what I've read most are using multiple coats of 50/50 clear preferably sprayed on to fill and seal the wings. After 3 or more coats and filling the pin holes the Polyspan can be lightly sanded using 400 or higher. Also my experience using the NAPA primer on the Polyspan is it too is not easily sanded off (unlike on hard surfaces) and can add too much weight. Some claim spraying on thinned clear and Zinc Stearate fills nicely and does sand (powder) off nicely.
Hopefully we'll get some recommendations on what is most preferable to use over Polyspan.
Steve
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Moitch,
Ah.... I reread your note, you used silkspan, my concerns still will apply.
Steve
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Hopefully we'll get some recommendations on what is most preferable to use over Polyspan.
I have had really good success with waiting to heat shrink the open areas until I had a coat of wet dope applied. It seals most of the pin holes and prevents the larger ones from opening up if you shrink it "wet" with as low a heat as you can. Polyspan is heat shrink, not moisture activated so, unlike silk or silkspan, it will continue to tighten when you hit it with heat over still "plastic" dope after the 1st coat and less likely to get those "exploding" pin holes that just ruin your day. It also lets you use non-tauting nitrate which, in my opinion fills faster.
Ken
Oops, I too missed the Silkspan, not Polyspan - never mind. You have to put a patch over the tear before there is too much dope on the wing. Tear a small one and get it on before it is too late to avoid a seam showing. If you have some lighter grade silkspan use that and put it on wet.
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Ken,
What is the recommended filler or "primer" coat used for Polyspan before applying the finish base coats?
Steve
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I always use a foam brush with polycrylic to keep from having brush marks.
Mike
Sent from my moto g(6) using Tapatalk
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Since this was my first attempt with Polycrylic, the panel I sanded through was actually sprayed with a couple of coats of polycrylic, not brushed. I won't do that again because it did not soak as thoroughly into the silkspan as all of the other panels where I brushed it on. It is brushed on the framework on the damaged panel, but the actual open bays have nothing by PC sprayed onto them. Live and learn.
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Ken,
What is the recommended filler or "primer" coat used for Polyspan before applying the finish base coats?
Steve
Over the open areas I don't use filler at all. I use a satin Rustoleum color in what will be my base coat, which is lighter than gloss act like filler and dries super fast. Sands well with 800+ and seems to fill what is left of the weave. It is simpler to touch up and shows flaws much better than gloss. The clear coat makes it all pretty. I hope our fetish for shiny planes ends before I do cause I like them better without a shine and they seem to fly better and NO HEAVY CLEAR COAT! I am willing to guess that this preference is not shared by many!
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Ken,
Please tell me more about what Rust-Oleum you use for a base coat?
Mike
Sent from my moto g(6) using Tapatalk
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Ken,
Please tell me more about what Rust-Oleum you use for a base coat?
Mike
Sent from my moto g(6) using Tapatalk
Rustoleum has a line of, for want of a better word, pastel and earth tones. I think it is in the 2x line and most are satin. By using your final color for both base coat, filler and primer you save a whole lot of steps as long as it is a light color like white. The plane in the pix has only three brushed coats of nitrate clear over polyspan by shrinking it wet and three light coats of Rustoleum satin white. 1st five sanded with 800 and touched up where needed. The blue is only two light coats. The great part is how easily touches up.
Wish I could be of more help but circumstance has forced me kicking and screaming into the MonoKote world.
Ken
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Ken,
I have been using the Rust-Oleum "Stops Rust" vs the Rust-Oleum 2X Ultra Coat in spray cans on the hard surfaces because it seems to work better (doesn't lift) when I lightly spray the edges using Rust-Oleum clear when using paint masks to reduce bleed. The Rust-Oleum does fill nicely though as you stated. Neither of these Rust-Oleum products are fuel proof only a little fuel resistive. The Stops Rust does however from what I found resists fuel discoloration better. You always must wipe off the fuel immediately. If you are using R-O I'm sure you are aware of all this.
I have not had good luck when using 10% nitro fuel after applying a final coat of clear butyrate. The clear will discolor if raw fuel gets on it so I have recently applied the KBS Diamond Finish from a spray can as a final to get better results. Also you cannot apply the hot clear dope over Rust-Oleum it will act like a paint stripper.
I just purchased a two part automotive finish I plan to use on a recent build I know will not be affected by the fuel.
Thanks for the tip on not priming the wings, I thought I saw a video somewhere of someone spraying the NAPA primer on the wing but it may have been a solid balsa covered wing with no fabric.
Steve
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Ken,
How long did you have to let the nitrate gas off before you sprayed it with the R-O?
Mike
Sent from my moto g(6) using Tapatalk
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Ken,
How long did you have to let the nitrate gas off before you sprayed it with the R-O?
Mike
Sent from my moto g(6) using Tapatalk
It was a week but I think it could have been less. The nitrate coats were 1 day apart and all of them brushed.
Ken
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I'm in the final assembly stage of the Ercoupe project I'm working on.
I think there's a half a dozen patches in the wing. One or two are from sand-throughs, at least one is from blithely setting the thing down over a bottle of CA glue that was sitting there waiting to poke the wing, and I can't remember exactly what the others were.
Oh -- and I just put covering onto my Legacy project. On one half of the wing top I must have dropped the Polyspan, because there's dirt grains between the polyspan and the wood. So those are going to have to be sanded out, picked out, or whatever, then patched over, and then I'm going to discover the joys of the Polyspan Fuzzies.
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I'm going to discover the joys of the Polyspan Fuzzies.
A right of passage.
Ken
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So those are going to have to be sanded out, picked out, or whatever, then patched over, and then I'm going to discover the joys of the Polyspan Fuzzies.
The fuzzies aren’t the major deal everybody led me to believe. They disappear pretty quickly with a coat or two of paint and fine sandpaper.
Of course it’s even less of a big deal if you don’t get any in the first place. Just gotta be careful about sanding down into it.