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Building Tips and technical articles. => Paint and finishing => Topic started by: Dudley Lang on July 04, 2010, 02:21:14 PM
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I live in an area where there are no stunt modelers to ask questions. I have built a Brodak Magician. I have covered it with silksspan and attached it with nitrate dope. The artical that I read said that you sand with 320 grade paper between each coat. It also said that you put on two to three coats sanding bbetween each coat. Then yoou apply your sanding sealer and sand again. I have sanded through the silkspan over several of the ribs and have had to patch these places. My question is: do you sand the all wood parts that are covered with silkspan such as the sheet stabilizer and not sand the covered wing or do you sand the entire airplane.
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Those few planes that I covered in silkspan, I sanded the open bays, but I sanded very carefully around the edges of all the ribs & spars -- any place where you have an edge in the surface is very easy to sand through, so you have to be exceedingly careful around them. This applies to any material you're painting -- I learned the "edge lesson" sanding out car paint jobs, then failed to apply it to my first silkspan job the first time around. I sanded the open bays freely in the middle of each bay, carefully up to the ribs, then I sanded the tops of the ribs with the paper wrapped around a finger, to try to hit just the top of the rib without putting any pressure on the edge.
The general idea is that you are putting a coat of paint onto a rough surface; the paint will smooth out very fine roughness to some degree, it'll contribute it's own roughness like a very smooth orange peel if you're spraying (or like a really rough orange peel if you spray too dry) or it'll leave brush marks, and it won't -- by itself -- smooth the 'long length' roughness at all.
Your job when sanding is to sand all of the high spots down to the paper and no farther. Once you've reached the paper in any area you must stop sanding that area until you've put more coats of paint on.
Note that this means that once you've put the paper on, you can no longer knock down the high spots with sanding -- you can only raise the low spots by filling them with paint. So you want to have all the high spots knocked down. Note also that it'll be easier to sand in the vicinity of the ribs after covering if you round the edges before you cover (note also that I did not figure out this lesson until after I covered my last silkspan-covered plane, and have waited 25 years to apply it!).
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Tim has a good point on rounding the edges of cap strips, leading and trailing edge sheeting etc. I also after applying 3 or 4 coats of dope to the silkspan will put additional dope on all capstrip and edges with a artists brush, usually 10 or more coats just for insurance. I saw that on one of Windy's tapes and I've had good luck doing it.
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Show me 10 folks who use silkspan and dope and I'll show you 10 different techniques. The important thing is to find the one that works for you. Unfortunately it may take a few planes to find the one you prefer. To cut to the chase - use 400 instead of 320 sandpaper. For the first few coats of clear, just knock off the "fuzz" that mysteriously appears when you first put dope to silkspan. After building up a few coats, you can get more serious sanding...however, don't get too serious until you put a base color coat on, usually grey, silver or a mixture of same. Be patient, don't worry if it's not a 20 pointer the first time out, that will come with practice. 8)
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I picked this up on the forum. Put on two coats of clear dope and skip a day. Sand very lightly, just getting a smooth feel and put on two more coats of clear dope. For me about the 8th coat it is starting to get a sheen. When it does I do a light sanding with one coat of clear dope. If staying with dope, put your sealer/filler on. When you think it is smooth put on a primer coat of grey or slilver. Now you will wonder where all the filler went as for me every little wood grain, any dings and whatever else you call it will show up. This is when you start working on getting a smooth finish. Untilthin don't even think of color.
Now if you are using someting other than dope for your primer/color coats I let the dope cure for a week or more. Some have gotten by with out the wait but, I guess I live in the wrong part of this great big old USA. H^^
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"Sand" the open bays of the wing with steel wool rather than sand paper. Run a magnet over it when you are finished to pick up all the tiny steel fuzzes.
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"Sand" the open bays of the wing with steel wool rather than sand paper. Run a magnet over it when you are finished to pick up all the tiny steel fuzzes.
That works pretty good once you get it flat. Until then, make some sandpaper "dots" with a paper punch or similar, and CA the dot to your finger. Much safer and easier to control than a sheet of sandpaper.
Brett
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"Sand" the open bays of the wing with steel wool rather than sand paper. Run a magnet over it when you are finished to pick up all the tiny steel fuzzes.
Which grade of wool are you using for this?
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That works pretty good once you get it flat. Until then, make some sandpaper "dots" with a paper punch or similar, and CA the dot to your finger. Much safer and easier to control than a sheet of sandpaper.
Brett
I buy PSA sticky back sandpaper rolls from the woodworking sources. You can cut little pieces that stick to your finger tips without the CA.. Also use the same stuff for the Great Planes sanding bars or any other custom sanding tools I make. I cut pieces about .75" x 1" and stick on finger tip and that works good for final feathering of fillets. The rolls are 4.5" wide by 10 yards long, come in grits from 40 to 320, around $15 / roll, but a roll last a long time.
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Hi Dudley,
Like Pete Cunha said, 10 people 10 different techniques! LOL!! None of which appear to me to be bad. ;D
I do not sand open bays until I have some dope built up on them, of course I never use ANY dope that isn't thinned at least 50%. So your mileage may vary.
Raw silkspan is just to easy to cut through with any thing. And sikspan is not a material that gets very rough when finishing. It will take "X" number of coats to fill it, anyway, and if it isn't filled, it will never look good. Sanding between the first few coats from raw silkspan up really has never seemed like a good idea to me. Of course, like I sdi, I don't always do things like everyone else, but if I say so myself, I do build light and the planes are shiney. Not 20 pointers but maybe in the 17-18 range when I really want to! LL~
Big Bear
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Tried this on my last dope finish and it worked out really well. The problem some of us have is not being able to tell when to quit sanding.. After your 3rd or 4th coat of clear mix in a little color with the clear. My airplane was going to be blue so I put enough blue in 4 ounces of clear to give it a light blue tint. Give it a coat of this tinted clear. Now you can go ahead and continue applying clear till you are ready for filler. When you mix the filler put a little white paint in so your filler coat is tinted white. Now you can sand the filler till you see blue (or whatever color you used) and stop before you sand through the covering.
A Polar Grey blocking coat will cover up the resulting mess plus when you start filling the buggers you discover after the first coat of grey you will know to stop sanding when you see the blue base.
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Hi Bob,
Great tip. I use Randolph's tinted clear. It has that effect.
Big Bear
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Something that a modeling friend of mine told me sometime ago, is when you get a hole in the s/span, tear your patch and it will be better hidden than cutting it as the frayed edges will blend in.
I know that this has nothing to do with the question, but if you use s/span you will have holes..!! :!
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Something that a modeling friend of mine told me sometime ago, is when you get a hole in the s/span, tear your patch and it will be better hidden than cutting it as the frayed edges will blend in.
I know that this has nothing to do with the question, but if you use s/span you will have holes..!! :!
Gil, that is 100% correct! ;D Much easier to fill/blend the torn edges.
Bill
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Hi Ty,
I still have some Rejuvenator, bought it for my 47 year old Smoothie! That tip is kinda like using sanding sealer on the ribs before you cover an I-Beamer. ;D
Bill
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Yep, except on I-beamers I use silk. I have a Minado under construction now. I'll send you photos. Won't fit on here. H^^
HI Ty,
It is going to be silk on the Airon. I just haven't sent my order to Dharma (or however you spell it! LOL!!) I am getting ready to update some pictures (not much!) on the Airon thread.
Just uploaded the camera.
Mongo
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I use the old Esaki type silk. I have some packages I paid $1.95 for many years ago. It is still available from freeflight and old timer suppliers but is up around $20 a yard now. With silk, the wood has to be well doped or you will get the open bays shiny and the ribs will still show the silk weave because the dope wicks through. Also, I put silk on quite wet, so the wood needs to be well sealed to keep the water out.