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Old 04-20-2014, 03:52 PM   #1
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Default Why cover with silk?

I bought a Phase3 F-16 and would like to cover and paint it. Everything I read about covering these foamies seems to focus on silk and WBPU resins. I have never used this technique, but I am very satisfied with the results I get from using half ounce fibreglass and Z-Poxy finishing resin. This stuff is easy to sand and gives a smooth finish. Is there a benefit to using silk and WBPU over fibreglass and finishing resin? Has finishing resin been used before with poor results?
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Old 04-20-2014, 04:15 PM   #2
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Silk goes on relatively easily and provides immense added strength. Silk has more than 10 times the tensile strength of steel by weight.

"Glueing" the silk to the foam with WBP paint essentially fiberglasses the plane with a cloth that is far stronger than fiberglass. You get a very stiff and strong model for a relatively modest increase in weight. The silk and WBP method is simply lighter than fiberglass and epoxy.
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Old 04-20-2014, 04:21 PM   #3
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Excellent, thanks. I will learn a new covering technique then. I will guess the WBPU sands with little difficulty?
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Old 04-20-2014, 04:24 PM   #4
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Silk + WBPU has a few advantages over glass and resin. First is cost, epoxy and glass costs more to do compared to silk and WBPU. Most people find WBPU easier to work with (with silk or glass). Getting a lightweight coating with resin and glass takes some know-how and many people get a lighter lay up with WBPU. Silk (and paper) both shrink while drying with WBPU. This imparts extra stiffness to the foam. It's possible to use this characteristic with a lighter structure to get lighter final weight.

If you like resin and glass, you should continue to use it. I've tried many methods to cover foam. Each has advantages but the one you have the most experience with tends to get the best results. Glass and resin has a reputation for being heavier but it's not if you know what you are doing.

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Old 04-20-2014, 04:41 PM   #5
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pmullen503, thanks for your reply. The more informed I can be, the better my decision. I like what you are saying. As I am new to the foamy world I am willing to stretch my bag of tricks open a little wider to add new techniques. I like the idea that silk will shrink, but I do have a concern with covering one side of flimsy parts such as vertical and horizontal stabs. Any secret to this to prevent warping?
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Old 04-20-2014, 05:06 PM   #6
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To prevent warping, don't use it on flimsy surfaces. If you must, then cover both sides with the grain of the material running in the same direction on both sides. Hang it vertically in still air and allow to dry slowly.

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Old 04-20-2014, 05:42 PM   #7
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I'd guess they say silk because silk is lighter. Lightweight silk is about 10g per M^2, so that's about 2/3rds of the weight of 1/2oz per sq yard glass cloth. Probably not so much the weight of the cloth itself but the weight of the resin it absorbs.

I'm sure on larger models light glass cloth would be perfectly ok.
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Old 04-21-2014, 01:28 AM   #8
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Dumb question here, what is WBPU? Water Based PolyUrethane? (just a guess)

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Old 04-21-2014, 02:32 AM   #9
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Flywheel, you are correct. Took me reading through six threads to figure that out.
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Old 04-21-2014, 02:34 AM   #10
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When you put it that way, it makes even more sense to go with silk and WBPU.
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Old 04-21-2014, 06:40 AM   #11
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When we say 'silk,' do we mean silk-silk?

Or does it have a special meaning in this context?

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Old 04-21-2014, 07:08 AM   #12
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Don't forget there is Glass cloth and Glass cloth ... the usual lay-up from light weight up to the heavy weight stuff used in anything from models up through boats etc. But there is also what is used as 'finishing cloth' that is more like very fine tissue ... in fact it can be so fine that you have to take extreme care when handling .. Any bit of hard skin or nail of your hand can ruin it so easily.

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Old 04-21-2014, 01:09 PM   #13
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Originally Posted by FlyWheel View Post
Dumb question here, what is WBPU? Water Based PolyUrethane? (just a guess)
WPBU is water based poly urethane as you said, but the actual product here in the US is Minn Wax. It's available at Home Depot and Lowes.


mclarkson When we say 'silk,' do we mean silk-silk?

Or does it have a special meaning in this context?


The silk I use is real silk. It's available from two good sources over here.
Thai silk:
http://www.thaisilks.com/product_inf...22fba3399425a4

Their silk product is tightly woven and good for covering solid areas.
It doesn't shrink much, if at all.

The second source I use is from Dhama Trading:
http://www.dharmatrading.com/fabric/...botai-5mm.html

It shrinks well. I have not noticed any shrinkage when applied over solid areas.

Both brands of silk "sucks into" cracks and crevices, almost like a second skin, so a smooth finish is desired before covering.

Lightweight Spackle or drywall filler works well for filling voids in foam without adding too much weight and it sands very well.

Here's an older thread on finishing foam
http://www.wattflyer.com/forums/showthread.php?t=22327
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Old 04-21-2014, 07:29 PM   #14
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Originally Posted by pd1 View Post
........The silk I use is real silk. It's available from two good sources over here.
Thai silk:
http://www.thaisilks.com/product_inf...22fba3399425a4

Their silk product is tightly woven and good for covering solid areas.
It doesn't shrink much, if at all.

The second source I use is from Dhama Trading:
http://www.dharmatrading.com/fabric/...botai-5mm.html

..........

Here's an older thread on finishing foam
http://www.wattflyer.com/forums/showthread.php?t=22327
PD got me hooked on his method. That thread he posted is very well done....great on topic post PD
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Old 04-21-2014, 07:41 PM   #15
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pd1, that was the original thread I started with. A very good read which provided helpful information. I posted to another one, "Just Bought Phase 3 F-16..." but never received a responds which is why I started this thread.

Thanks for the information on where to get silk.
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Old 04-22-2014, 03:47 AM   #16
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Thanks for the info. I've only ever used very lightweight (0.55oz) glass and that only a few times.

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Old 05-08-2014, 03:16 AM   #17
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Default New to Silk on Foam

Following this thread - what silk are we looking for on the aforementioned manufacturers' websites? I would guess I would be in the wrong place if I was in the lingerie area of the website?
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Old 05-08-2014, 04:35 AM   #18
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Originally Posted by PeterGregory View Post
Following this thread - what silk are we looking for on the aforementioned manufacturers' websites? I would guess I would be in the wrong place if I was in the lingerie area of the website?
I have no idea. I have not been able to get to the big city to buy any yet.
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Old 05-08-2014, 05:04 AM   #19
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Originally Posted by PeterGregory View Post
Following this thread - what silk are we looking for on the aforementioned manufacturers' websites? I would guess I would be in the wrong place if I was in the lingerie area of the website?
Dharma Trading Company has the silk in several weights. They call it Habotai silk and others just call it Chinese silk. I bought some of their lightest weight and it came from Malaysia in about 10 days; used some to cover a wing the old way with nitrate dope and it worked great.

Look up www.dharmatrading.com.

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Old 05-08-2014, 06:57 AM   #20
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Originally Posted by PeterGregory View Post
Following this thread - what silk are we looking for on the aforementioned manufacturers' websites? I would guess I would be in the wrong place if I was in the lingerie area of the website?
http://www.dharmatrading.com/fabric/...botai-5mm.html

That should take you to the correct page.....
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Old 05-09-2014, 01:55 AM   #21
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Thanks pd1. I ordered several yards from Thai silk and Darma trading. Darma is less expensive and ships cheaper, both packs arrived in the mail on the same day.

Next up, dying with Rit just for giggles. Dying requires a few hoops to jump thru to "fix" the dye so it won't wash out, but hey - I'm going to plaster the silk with nitrate dope so will not stress about "fixing" the dye.

I like silk. Way back when I had a Goldberg Jr Skylane silk covered and it was tough. One flight went bad and the Cox Medallion .049 drove it into the schoolyard grass at about a 45 degree angle. Ouch! Only damage on the plane was a cut in the cowl area where - believe it or not - the Skylane had landed (crashed) on a dime, and said dime was implanted in the balsa cowl.

The silk Skylane was handed down to several novice young uns over the years, may still be flying somewhere . . . silk, it ain't just for sexy undies.
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Old 05-09-2014, 01:58 AM   #22
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The silk from Thai Silks is pre-shrunk. That can create issues when trying to get a smooth surface, but it can also prevent the shrinkage from twisting your airplane.

Applying silk is an art form...
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Old 05-09-2014, 02:07 PM   #23
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I found this at Dharma Trading web site.

"• 100% Habotai Silk
• 5mm, 36", 45", or 55" wide
• You can dye this with Acid Dyes
I've used plain Ritt Dye and had good luck.

• We found that this shrinks 8% in Length and 1% in Width

An explanation of "shrinkage".
Shrinkage is a factor in planning how much fabric you need for a project. To help you, we took a 1/2 yard of every one of our fabrics, measured the length and width, washed it in a machine with very hot water, dried it in a dryer set on very hot setting, and then measured it again.
Then we calculated the % shrinkage in length and width which we are reporting to you.
Please be absolutely clear!
We think it's the worst case scenario.
This is only our experience and yours will vary.
Please do not take this as some sort of guarantee about how much the fabric will or will not shrink in your circumstances.
Most fabric shrinks when washed and dried, especially undyed fabrics such as the ones that Dharma sells. Fabrics that go through a dyeing process will also go through a shrinkage process. Dyed fabrics that you would normally purchase in a fabric store have already gone through a dyeing process and therefore have gone through a preliminary shrinkage process. So when you buy undyed fabric from Dharma, you're buying fabric that has never been shrunk."
-------------------------------------------------

This is more for apparel than models, but If you are covering over open structure, like a wing, run the grain lengthwise along the span of the wing and the silk won't pull down between the ribs.
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