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Silk Covering Techniques

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Old 08-14-2010, 09:07 PM
  #51  
mred33
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Default RE: Silk Covering Techniques

You can get fine steelwool at most local hardware stors, but it is FINE, not that stuff you use to clean your pots and pans with like SOS. Also, dope has never been 100% fuel proof and spilling straight fule on any doped finish is not a good thing to happen. Wype that off as soon as you can. I use paper towels and Windex to clean my planes and it seems to work great. Most of the people I fly with use that to clean a plane, even with a Monokote covering. You need to find the SOFT towels though, not he paper towels that act like sandpaper. Some people use a cotton cloth to clean their planes off with and it's a little easier on the finish that way. Even using the good soft towels they will scratch a Monokote covering after awhile.

As for clear doping a plans only, you really need something else over clear to keep the fuel from soaking in and UV protection. Normal colored dope seems to work ok for fule proofing it, but then again dope is NOT 100% fuel proof. By fuel proof we are talking about exhust gas with mostly oil in it and not the fuel itself. That was what they are talking about when they say fuel proof, not straight fuel spilled on it and never leave it sit for a few days like that. You see what happens if you do.

Any time you do a test like this, use something for the test besides your airplane. Testing is done to find problems and if it is your plane that is being tested like you did, then you see what happens with a bad test on a plane. Just make a small square of wood or something like that about 4" to 6" square and if the test you do comes out bad, then you didn't hurt anything important. Iuse scrap lumber for this kind of thing because it is cheap. I don't wast balsa on a test sample. The only planes Ihave ever flow that were just clear doped were combat C/L planes and they didn't last very long anyway. You really need something for UVprotection over your clear to keep the sun from breaking it down. Ihave heard of a UV protector that you can add to clear, but Inever used any and don't really know what they are using.

If you are going to use any kind of paint on your plane, always do a test sample first to see what fuel does to it. Some paints will curl up at the first hit of fuel and some will last quite a while. One of the better paints that Ihave heard of is Rustolium. The best that Ihave found is to put a good coat of clear epoxy paint on as the last coat.

As for the air brush, Ijust used a Badger paint set that has a 1 or 2 oz cottle on it and they are not all that great for fine painting, but work great for covering a large area. You can get one from Harbor Freight that is like a Badger and cost quite a bit less. They are about as good as the old Badger sets though, which is to say, they aren't THATgreat. If you want a good air brush that does fine painting and fading in on letters and things like that, you are going to need a good quality double action airbrush and they will run around $100.00 for one. Most people don't do that kind of painting on an airplane that would require that kind of brush.

As for sanding an open area of a wing, you will need to develop a LITEtouch or you will cut through the silk or what ever you are using for the covering. All Ican say is, try it on an open section of a box like I told you to make for testing and practice on that, not your wing. If you start on the wing the first time, you will sand through the covering at the rib area fast. Even using steelwool instead of sandpaper you need a lite touch. Your not trying to sand this down on one pass. It takes a lot of time to sand down a finish so don't even think you can rush it. The first time you try and rush it, you will sand right through the silk and it will more then likely be where it goes over a rib. Your only sanding down the paint to smooth it and get rid of brush marks, not sand it off. Iuse a primer over my clear and sand that until it's almost gone, but that is to fill any pin holes and things like that, not to leave a bunch of heavy paint on your plane. You should see very little of the primer left after you get finished sanding it. DON"T put it on heavy, or you will just have that much more to sand off.

When putting a color coat on, I sand it down with 400 and then 600 and see if Istill have good coverage after that. If you sand through the color to far it will look blochy and you will need to add another coat of color again. Your only trying to get it smooth, not sand through it, so use a lite touch on that. When putting color on anything, Inormally put two fast coats on and by fast Imean that the first coat is not really tacky anymore, but not really dry either. Depending on how far I want to go with a finish, Imay put another coat on and then let it set for about a week before you do the final sanding. To do it right and get a GREATfinish takes some people a month or better to do one, but they look like glass when done properly. I very seldon take one that far. When finished with all your painting and you think you are done, then let it set for at least a week before you go fly it. That lets the dope dry properly so it is better at resisting fuel. It's better to let it sit for two weeks, but not everyone can let it sit that long without flying it. Give it a week at least though. Dope and most other paints don't dry over night like they feel like. It may look and feel dry, but it isn't. I'm not really sure if dope will ever really dry or stop shrinking. I think that goes on forever, but it's not soemthing you can see happening.

For our use and flying, a week is enough, but wype the plane down when you get back to the pits, don't let it sit there all day with oil spreading more and more on each flight. Just give it a quick wype down at the end of your flight and clean it really good BEFOREyou go home. That plane should be CLEANwhen you put it in the car to go home. That encludes the engine bay more so then anything. That will more then likely have a deep place where oil will sit and just keeps getting more as you fly during the day. I use 409 to fluse it out and I ALWYS us finishing epoxy to cover it so the fuel doesn't soak in and Ido that to the fuel tank area too.

If you have any more questions, fire away. Someone will answer them.

Ed
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Old 08-14-2010, 09:36 PM
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Default RE: Silk Covering Techniques

Thank you again, Ed, for your replies.

The wing we used that appeared we were using a 'working' wing was an old messed up North Star wing I had sitting collecting dust and mold in the pole barn, so no harm done on the fuel test. We're gonna work on recovering this Super Sportster and post some pics as we go along.

Wish us luck! lol
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Old 08-15-2010, 12:23 AM
  #53  
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Default RE: Silk Covering Techniques

Good luck on the Supersportster. I have a couple of them and they fly great. I did the first with just a change of motors, but the second one Irecoverd in PT-19 colors. I got lazy and just did it in Monokote. I got one of the very last old ones, because right after Igot mine, they came out with the new one. My timing stinks..................... Glad that wing was just a junker. It would be a shame to mess up a good one like that.

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Old 08-15-2010, 07:19 PM
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Default RE: Silk Covering Techniques

OH! I know what I was going to ask ..

How many coats of dope is enough?  One of the guys at our field says "Dope it 'till it shines" .. but on the North Star wing, that was like 10-12 coats and I still had to take a paper towel soaked in thinner to 'buff' a shine to it.  This is using 1:1 thinned butyrate dope.
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Old 08-15-2010, 11:52 PM
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Default RE: Silk Covering Techniques


ORIGINAL: virgomoon

OH! I know what I was going to ask ..
How many coats of dope is enough? One of the guys at our field says "Dope it 'till it shines" .. but on the North Star wing, that was like 10-12 coats and I still had to take a paper towel soaked in thinner to 'buff' a shine to it. This is using 1:1 thinned butyrate dope.
Well now, that depends. What kind of finish are you looking to get? Do you want a show room finish that looks a foot deep and you can shave in, or are you just looking for a decent finish that you go fly all the time and don't care if it's not a really shinny finish. My normal finish is about 3 coats of clear and check it with a light in back of it and look for a stedy sheen all over it. If you see any spots of light that stand out, the weve is not filled there and you will need one or two more coats depending on the weve of the fabric you are using. The silk is going to have a weve to it and this weve is what you are trying to seal all over the surface. Just remember one thing. Paint is weight. The more you put on the more the plane will weigh and the worse it will fly. If you just have a very few dots that stand out hear and there, then it is time to prime it. This should finish the fill of the weve and those small open areas should all be filled with the primer coat. Use the light again after you sand the primer down and see if you have any of those dots that stand out still. If so, you can shoot some more primer just on those spots and then sand that area down to get the final fill of the weve. You should have VERYlittle primer left on the surface after you finish sanding it down and Imean very little. Primer is heavy and you don't want any more on the plane then you really need. It's really hard to tell you in words what the surface will look like when the primer is sanded off, but you should be able to see thru the primer in all areas like it is transparent. Mostly what you should have is clear dope left. If you have any ringing on the primer, you will need to clean that spot up as good as you can. It will ring when you have some kind of contamination there and the paint it not sticking to that spot. Isand with thinner or alcohol on those spots to try and get that off. The best thing you can do is use those disposable gluves when you first start your covering so you don't get oil from your hand on it.

Ilay my wing flat when Istart painting and don't do the other side until it is tack free on the first side and then turn it over and do the other side. Same with the fuselage, Turn it on it's side and do one side and then do the other. That stops a lot of the running if you get to much paint on one area. Runs and sags are a real bummer to get out and make it look good. I normally spot paint with primer if Isee a spot of light shimming through that area and then sand it off. What you are looking for is a filled weve and a flat smooth surface, not a shinny one. You don't worry about shinny until the last coat. When you put your first color coat on, that needs to be sanded down too with something like 400 used wet, but this is a lite sanding, not trying to cut through the paint. All you are trying to do is get it level and smooth. Don't even think about trying to get any coat shinny while you are painting until the very last coat. That's the one you what shinny. Ilike to use a base color of some kind. Sometimes Iuse white and sometime I use silver. It just depends on how I feel amd what I want to see. Some paints are translucent and I don't think you will ever get it to cover right without a base coat. Most colors are great and cover in one or two coats, but then there is that one that can bite you. Always start with the light colors and go to the darker colors after that.

Once you get a good coverage and it's sanded down good and there are no thin spots showing through, let it set for a couple of days. Now mask it off and start painting the trim on. Inormally spray a lite coat of clear over the tape to seal the edges so the trim colors will not bleed under the tape. If you are painting all straight lines for trim, the width of the tape doesn't make any difference, but it you are using curves, use a narrow tape for that. Inormally use 1/8" wide tape because it will bend good with out folding up in a turn. That looks pretty bad after you pull the tape off. Put enough trim color coats on to make it a good solid color and not thin in some areas. You want an even coat. Let it set until the paint is tack free and take the tape off by pulling in back over itself. DON"Tlift it straight up or just as bad , at an angle to you. You want that tape to cut through the paint as you pull it off. Now comes the fun part. You get to sand some more with 400 and then 600 and don't cut through the paint and take it off, you just want to take the ridges off where the tape was. If you run your had over the area, it should feel smooth all the way across. Now let it set for a couple of days and then get clear out again. I put two coats of clear on and fast. I just let the first coat get tacky and then put the second coat on and both of these should be wet coats. Be careful you don't get any runs in this coat. Now let it set for a couple of days and sand it down again with 600 snadpaper. All you are trying to do is cut the glaze off so it is not shinny. let it set for a couple of days and do that again with a couple more coats of clear. The first two coats I thin 50 50 and the last two Ithin a little more. Maybe 60 40 and make SUREyou don't get any runs in it. Now let it set for at least a week and two weeks is better. Now you get the polishing compound out and rub this coat to really make it shine. Some people call that rubbing compound, but it is the very FINEgrade of rubbing compound. Most of the polishing compound that I have used is white. Now you can get some really good wax out and put a good wax job on it. After you get done with this it should be nice and shinny. It should feel like plastic and should have a good shine to it. If you can find a solid past wax with 100% Caranuba wax , that is the best. I think Mother's is 100% or close to it. It cost a little more then the other wax, but it is much better.

The best finish Ithink is to skip the dope clear after the trim and use epoxy clear. I used to use Hobbypoxy on mine, but they don't make that any more. The still make epoxy paint though.

Now you can hang it on your wall in the living room and admire your nice shinny plane for a week or until you can't stand it any more and have to go fly it. Now go take a bunch of pictures of it before you fly it so you know what it looked like the very first time you flew it. You never know what is going to happen on that first flight, so take the picture first then go fly. After you land, clean it off and don't let that oil and gunk sit on the plane before you go fly it agian. Wype it down after every flight and if you use a nice cotten cloth, it should hold it's shine for quite a while. If it gets to looking a little drab, wax it down again and you should have a plane that looks new again.

Now that you have read all of this, go here and read this; http://www.airfieldmodels.com/inform...oxy_paints.htm
The last coat of clear should be done with Klass Kote to really make it fuel proof and you can start painting the plane with this right after the primer is ready to be painted if you want, or you can use their primer. The only problem with this paint is the amount of colors available. There are no where near the colors that you can get from dope. Check out this for the color selection guide; http://brodak.com/images/Shop/BrodakPaint.pdf One thing that is great about this dope is they have candy colors. I don't know if you have ever worked with candy colors, but they make a fantastic mess, or a fantastic paint job. Ihave seen some that look a foot deep and other that look like you know what. It all depends on how much work you put into it and no matter what paint you use, you are goign to put some work into it. You can also read this to get some more information. http://www.airfieldmodels.com/inform..._materials.htm

That site is full of VERYuseful information on all kinds of things. Just kick around and look at what they have and you may find that it has a lot more to offer then most sites and may take you a while to get through everything. Lots and lots of good information here.

However you decide to finish your palne, good luck. One thing to remember is this. If this is your first real finish other then iron on plastic, then you are in for some eye opening reading and work. It is not something that is done in one night or even a weekend. Painting a modle takes practice and the only way to get the experance is to do it. You can get a decent finish your first time if you take your time, but to get a really great finish takes a while to learn and you do have to learn how. It's not something you read about, it's you own effort that makes the finish and the more effort you put in the better the outcome. What ever you do, good luck and don't be afriad to ask.

Ed

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Old 08-19-2010, 07:59 PM
  #56  
virgomoon
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Default RE: Silk Covering Techniques

I realized I've got more questions about covering this Super Sportster than I originally thought. I'm attaching some pictures of it naked. What covering pattern would you suggest? I mean, I think I have a good idea of what panels I would cover how and in what order, but I just want to make sure I'm not too far off base.

My thinking is one panel per side of the horizontal and vertical stab. Then a small piece running the length of the area between the two on the top of the fuselage. Then one panel per entire side of the fuselage joining at the top of the stringers and along the topmost part of the front fuse (in front of the cockpit) and along the bottom center. Then 4 panels for the wings (2 pieces on top, 2 on bottom joining in the center).
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Old 08-19-2010, 08:17 PM
  #57  
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Default RE: Silk Covering Techniques

This is similar. You can see the first piece of silk on the fuse covers most of the fuse.

The wing can be four panels or the bottom as one piece. The top of the wing is easier in two pieces.

I covered this in one piece, but I had to split the top center to allow for dihedral.
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Old 08-19-2010, 11:43 PM
  #58  
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Default RE: Silk Covering Techniques

It looks good from what Ican see in the pictures. However, I would have covered that open section in back of the cocpit with one piece going from one side over the top and to the other side. That way you don't wind up with a seam on an open structure that has to be sanded down. To me it is just easier to it do that way and that is the way I always cover open structure. Iancor it to the sides instead of that top stringer. You can still blend that seam in on top, but it is a little harder for me to do. That's just me though. Some people do it your way and it comes out fine. On the wing, I always use 4 pieces and the stab the same the the rudder I use two. As for the fuselage, I just cover it any way that allows me to get a smooth covering. It doesn't make any difference how many sections you use as long as you blend them in later so you can't see them. In the end, it all comes out the same though, so have at it and get it covered good so you can start on the paint job. That's where the fun really begins, or at least for me. Ilove painting a plane, even if it's just dope.

Ed
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Old 08-20-2010, 05:38 AM
  #59  
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Default RE: Silk Covering Techniques

I've placed the seam both places. I like doing it on the top stringer so I can fold a little silk over the stringer and it won't get re wet when I do the other side. But that just boils down to personal preference.

Covering the top with one piece works equally as well.
Personal preferences.
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Old 08-20-2010, 11:00 AM
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Default RE: Silk Covering Techniques


ORIGINAL: pd1

I've placed the seam both places. I like doing it on the top stringer so I can fold a little silk over the stringer and it won't get re wet when I do the other side. But that just boils down to personal preference.

Covering the top with one piece works equally as well.
Personal preferences.
I agree 100% with you. Like Isaid, Iknow some people that do it that way and I did try it, but I didn't like it as much. Like you said, personal preferences and I would never try to agrue anyone out of doing it another way of it works for them. From what Ican see in his pictures he is doing a great job on covering and Ican't fault him for his method, just threw in my 2 cents worth.

Ed

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Old 04-13-2011, 09:51 AM
  #61  
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Default RE: Silk Covering Techniques

I have three planes to cover - two foam and the other a Mustang 450 electric conversion that has a balsa sheeted foam wing and balsa fuse. I want to use silk in place of 1/2 oz glass cloth to keep the planes light but strong. Has anyone used 5mm or similar silk with a low viscosity epoxy on foam or balsa sheeted planes? If not, does anyone have any ideas on what weight silk and supplies I should use?
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Old 04-13-2011, 11:58 AM
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Default RE: Silk Covering Techniques

I've covered foam planes with 5 mm silk and wbpu. I've also used silkspan and I like silk better.

Here's a build thread I did with silk on a foam plane.

http://www.wattflyer.com/forums/showthread.php?t=22327

Paul
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Old 04-13-2011, 01:08 PM
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Default RE: Silk Covering Techniques

Ihave covered things with silkspan and gave that up years ago for silk. Either heavy of lite silk, depending on the structure. On strong structure, you can use the heaver silk and on the lite structure you should go to lite weight silk. Iam trying something that is new to me, but it has been around awhile. It's called polyspan and is a polyester covering that you can apply just like silk, but it is stroger and cheaper from what Ihave been resding. http://www.faimodelsupply.com/starline-polyspan.htm You can read this information here about it and make up your own mine about it. It comes in 20"X12ft sections for $15.00 and that is way cheaper then silk now days. You use it just like silk with one exception. It is water proof, so you don't shrink it with water like you do silk and silkspan. You cover your model with it and the dope shrinks it and if you don't get all the wrinkles out, you can use your monokote iron on it to shrink it even more. On foam parts, you should be able to work out the wrinkles while you are applying the dope or whatever you use to put it on with. Since dope may very well eat your foam, you can use wbpu to put it on with, while the balsa structure you can use either that or dope. From everything Ihave read, it fills easier then silk and it comes out about the same as silkspan weight wise when you finish it. Iam about to use it on one of my planes for the first time, so Ican't tell you a lot about it, but everything Ihave read says that it is every bit as good as silk without the expense of silk. You apply it and finishe it just like silk with one exception. You don't water shrink it. Other then that, you treat it just like silk.

Good luck on your new plane and let us know how it comes out. If you have anymore questions, ask away. Someone will answer them.

Ed
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Old 04-15-2012, 12:48 PM
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Default RE: Silk Covering Techniques

Hi!
sorry my limited english

after dope dry, can i use paint for car 2 component...paint+catalized i know this paint do not need clear fuelprof.. thank you


ORIGINAL: pd1


Here's a couple of things I've found out about silk and dope.

Nitrate can't be applied over butyrate. It will react and ruin your finish.
Nitrate is very flammable compared to butyrate.
Nitrate has a little better adhesive qualities compared to butyrate.
Nitrate requires additional fuel proofing.
Nitrate stops shrinking after a couple of days.
Butyrate shrinks for a long, long time.

Covering. I don't use nitrate anymore, personal preference, so to increase the adhesiveness of the butyrate I coat the bare structure with butyrate until the wood picks up a shine.

Then apply my silk. Spray the silk with water and get the wrinkles out.
I use a lot of thinner with just a little dope to stick the silk.
The thinner passes through the silk and softens the dope underneath sticking the silk down.

If you accidentally get some of the thinned dope on the silk, there is not enough dope to curl the silk.
Thick dope will curl the silk as it drys.

Using dope while the silk is still wet will cause the dope to blush. It will actually turn white.
Let all the water dry off the silk before doping too much.

If it is a day with high humidity, the dope may blush again. A couple of drops of retarder will stop that.
Sig sells retarder in small bottles.

If you hold a wing horizontal while doping, especially with dope that hasn't been thinned a lot, the dope will drip through and make an ugly ''ring'' on the other side of the wing.

To avoid that when doing wing panels, just use very thin dope and hold the surface vertical.
The thinned dope will not leave a ring, and if the panel is vertical the dope will stay on the side you are doping.
On the last couple of coats of clear I add a couple of drops of Castor oil to the clear dope. It will act as a plasticizer and will slow dope from drying out over a long time.

Silk. I've found that there are at least two different silks that shrink different from each other.
The silk from Thai silk seems to be pre shrunk and doesn't shrink much if at all after covering.
This is good for delicate structures.

http://www.thaisilks.com/product_inf...22fba3399425a4

The silk I like from there is the 5mm 021F-000 Habotai.

If you want silk that shrinks more, the silk from Dharma Trading is for you.
It's great for stronger structures.

http://www.dharmatrading.com/html/eng/3374-AA.shtml

I use the 5mm. HS536 or the HS545 same but 45 inches wide.

I've found the 5mm silk is lighter than any other covering, including tissue and the weave is so tight that it doesn't take much clear to fill.

Before you ask,mm is not milimeters. ''MM is Momme.
Momme (pronounced ''mommy'' and abbreviated ''mm'') expresses the weight in pounds of a piece of material of size 45 inches by 100 yards. So, for example, a 50 yd. bolt of our 5mm 45'' Habotai Silk fabric (#HS545) would weigh 2.5 lbs. (plus the weight of the cardboard tube it is wrapped around, of course).
The higher the momme, the heavier and stronger the fabric. Anything above 28 momme is considered heavy-weight and generally used for curtains or heavier outer-garments. Silk under 20 momme is considered lightweight, and generally used for light blouses with a chiffon feel. Medium-weight silk (20 to 28 momme) is excellent for silk scarves, furnishings, wedding dresses and the ultimate luxury of silk sheets.'' Dharma Trading.


5 mm silk is extremely light.
A sheet 45 inches wide by 300 feet long would only weigh 5 pounds.

Drying out and rot. Unless you leave the silk in direct sunlight, the silk won't rot.
What actually happens over time the dope becomes hard and brittle. The silk is saturated with the dope and when the dope cracks, so does the silk.
I just started removing silk that was applied 40 years ago. The silk is fine, the dope isn't.

Silk has a ''grain'' to it. It usually has a finished edge on one side of the piece. The grain is parallel to that edge.
Run the grain spanwise on a wing across the ribs.
If you run the grain chordwise, with the ribs, the silk will pull down between the ribs and look odd.
Silk shrinks more with the grain than across it.


If you thin dope sufficiently, and use a good brush, it will not leave brushmarks.
I use a camels hair brush, most hobby shops carry them.
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Old 04-15-2012, 05:04 PM
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I've used automotive primer from a spray can over butyrate without any adverse reaction.
I've then used various paints over the primer without any reaction.

I have not tried two part paint with a catalyst.

I would be concerned over open areas like a wing structure.
I don't know if it would be flexible enough to keep from cracking.
Over sheeted areas, I don't think there would be a problem.


This plane has the auto primer.

Paul
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Old 04-16-2012, 05:33 AM
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Default RE: Silk Covering Techniques

Iused a primer that looks like the one you used, same color anyway, and it was like painting on led. Boy was it heavy. Isanded most of it off before painting it and it turned out pretty good. Itried that paint with catalyst once a long time ago and it cracked on the open structure. I don't know if this will do that same thing mine did, but I would hate to take a chance on it cracking like mine did. Ieven got a few cracks on the fuselage which was solid structure. Guess it was flexing to much for that paint. From then on Ijust used normal paint and a little plastiscizer mixed in to keep it from cracking on the plane. Istarted getting lazy for awhile there and started using MonoKote and just can't get a good covering job like ido with paint. Ihave started going back to paint on some of mine now and it is much easier to make it look good with paint. The only 2 part paint that I never got cracks in was Epoxy. That was some good stuff, but kind of hard to work with compaired to dope.

Ed
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Old 04-16-2012, 06:26 AM
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Default RE: Silk Covering Techniques

Hi Ed,
The primer I used is Krylon brown in the rattle can. After letting it sit for 24 hours is wet sands beautifully, and the edges feather real well.

I just tried Rustoleum primer, it is heavy and doesn't sand well, I'm so disappointed with the Rustoleum I'm going to sand it all off and go back to Krylon.

Color dope is getting harder to find and I'm always looking for alternatives.


Paul
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Old 04-16-2012, 09:21 AM
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It's getting to the point that dope cost to much and other paints are cheaper. About the only dope Iuse now is clear for filling the weve of the silk. After that Ijust use whatever I feel like at the time. Istarted out using Pactra when Iwas younger and that is all Iever used. Now they are gone and most of the other dopes are either gone or high priced. Randolph has a good price on clear and Iget a Quart at a time, but other then clear, Iuse other paints now. Ihave tried using dope, but it just cost to much and as much as Ilike it, there are so many paints out there that cost less then half of what dope cost that I have pretty much given up on dope. Ireally liked using dope though and still wish Icould find a good sorce of decent priced dope in pint or quart cans. Those little 4 oz jars just cost to much. That makes a quart about $64.00 and that is just to much.

Ed
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Old 04-17-2012, 06:15 AM
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"everything I have read says that it is every bit as good as silk without the expense of silk. "

I cannot accept that. Silk is fabric; silkspan is a paper product. I see no way they can be as good.

Les
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Old 04-17-2012, 07:08 AM
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Default RE: Silk Covering Techniques


ORIGINAL: LesUyeda

''everything I have read says that it is every bit as good as silk without the expense of silk. ''

I cannot accept that. Silk is fabric; silkspan is a paper product. I see no way they can be as good.

Les

Les,

I think Ed was comparing Polyspan to silk. In some ways, the polyspan is pretty good stuff. Easy to work, just like silkspan. Very easy to shrink with an iron. And it doesn't deteriorate due to sunlight as rapidly as silk. The down side to polyspan is that its strength is not symmetrical. It's quite strong in one direction and no better than silkspan in the other direction. I've covered a few old timer models with polyspan and had problems with puncturing the covering by picking the model up with my thumb across a spar or stringer. If you press too hard the covering just splits along any hard edge that happens to be parallel to the grain.

Dick
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Old 04-17-2012, 06:23 PM
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Default RE: Silk Covering Techniques

ORIGINAL: LesUyeda

"everything I have read says that it is every bit as good as silk without the expense of silk. "

I cannot accept that. Silk is fabric; silkspan is a paper product. I see no way they can be as good.

Les
Iwas talking about polyspan and I will admit that Ihaven't used it very long. I am still in the process of learning how it works and if it will hold up. So far Ihave not punched any holes in it, but that doesn't mean that Iwon't later. Inever pick up a plane by putting pressure on the covering. Ilearned that back in the days of silkspan with Iwas a kid and that was all I could afford. Itreat all planes the same and carefully lift it by the bottom of the fuselage and wing, but not putting much pressure on any one point. Ireally like silkspan, but I'll be the first to admit that it doesn't hold up all that good. Ihave had planes that lasted a couple of years with silkspan, but not more. They just start attracting holes for some reason. Silk is my all time favorite and if polyspan doesn't hold up, then Iwill go back to it. Ijust had to try it and see what it was all about. Ihave used nylon before, but it is a little hard to work with and not much fun. Kind of heavy too.

Ed

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Old 04-17-2012, 07:38 PM
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Default RE: Silk Covering Techniques



I was talking about polyspan and I will admit that I haven't used it very long. I am still in the process of learning how it works and if it will hold up. So far I have not punched any holes in it, but that doesn't mean that I won't later. I never pick up a plane by putting pressure on the covering. I learned that back in the days of silkspan with I was a kid and that was all I could afford. I treat all planes the same and carefully lift it by the bottom of the fuselage and wing, but not putting much pressure on any one point. I really like silkspan, but I'll be the first to admit that it doesn't hold up all that good. I have had planes that lasted a couple of years with silkspan, but not more. They just start attracting holes for some reason. Silk is my all time favorite and if polyspan doesn't hold up, then I will go back to it. I just had to try it and see what it was all about. I have used nylon before, but it is a little hard to work with and not much fun. Kind of heavy too.

Ed


[/quote]

In all fairness I should point out that polyspan has some good features. It is nowhere near as stretchy as the mylar films, so you can expect to gain some rigidity from polyspan. It takes very little dope to fill. Overall, a polyspan cover job can be very light. And it really does shrink nicely with a monokote iron.

But have you tried just taking a raw sample of polyspan and giving it a tensile test ? In one direction it's as strong or stronger than silk. In the other direction it's no better than silkspan. The first time I saw polyspan was at a hobby show. The guy in the booth had little samples with which he would give a mighty pull to demonstrate how strong it was. Then he would hand the sample to an onlooker and offer to let him try it. When he handed me a piece, I already knew how strong it was in the long direction from watching others. So I turned my sample 90° and began to give it a tug. The vendor got wide eyed and said, "DON'T DO THAT !"

Regarding how you pick up a model, I agree that it's always best to pick up in a sheeted area such as under the mid fuselage. But most of my models are old timers with very little sheeting. Sometimes at the end of the day when I'm removing a wing and the wind is blowing there is no good place to grab. Same thing as on a silkspan free flight: wings in a breeze are really tough to hang onto sometimes.

Dick
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Old 04-18-2012, 04:42 AM
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Default RE: Silk Covering Techniques

I used Polyspan to cover an .09 powered Petite Parasol (MAN 3/66). The wing has a lot of compound curves made of balsa block, with open frame between ribs. It worked beautifully. I had to take my time and stretch it going around curves, but it worked. Despite the grain, I have found it to be WAY stronger than silkspan, and silkspan was all I used back when I did control line. I agree that it takes dope well, and yes, it is light. This plane came out to 27 ounces despite a colored dope finish. I think it's great stuff.

Jim
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Old 04-18-2012, 06:36 PM
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Default RE: Silk Covering Techniques

Iwill admist that Inever gave it the old pull test, so Igrabed a piece of mine and gave it a tug. Tore in both directions pretty easy. Not as easy as silkspan, but MUCHeasier then silk. Ionly have it on one plane that is flying right now and one that is waiting to fly. The other is still under construction, so Istill have not see how it will hold up to the long haul. Maybe it will get more strength after it is doped and painted. Haven't torn any of it yet handling it, so I'll just have to wait and see I guess.

Ed
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Old 04-18-2012, 07:00 PM
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Default RE: Silk Covering Techniques

I don't think silk has more puncture resistance than Polyspan. Maybe less. No scientific comparisons, but I've used both.
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