Covering foam using Poly C and Tissue

[Chris F]

I have the GWS FW-190 and have decided to use the Poly C and tissue method as mentioned in Matt Halton's thread
http://www.rcgroups.com/forums/showthread.php?t=536128&page=4
Unfortunately Matt hasn't got to the Poly C and tissue part of the build so I am hoping someone can give me some instruction on how to do it.

[Water Boy]

I have tried something like this on a spare wing I made. Instead of using tissue paper I tried newspaper. But what I did was put a light coat of WBPU onto the foam, then placed the paper onto that smoothing it out. Be careful not to rip the paper. Then put more WBPU on top of that. Pretty much just like paper mache.

[Chris F]

How was the finish? Did it look ok?

[Water Boy]

The finish was not that bad, a little wrinkly but I guess you could sand it with some super fine grit paper. Of course this was just a rush job. I really did'nt plan on using it for anything. I would say practice on some scrap foam.

[J Morgan]

Silkspan/poly makes a great, light finish. I used it on the Tigercat. Brush poly on the silkspan and when you come to difficult curves, tear( do not cut) the silkspan to make it conform. You will get some wrinkles, simply sand them out when dry. Then give two add'l coats of full strength poly with the last coat wet sanded. It is then ready for paint.

J

[Water Boy]

J, Why tear? Does this allow it to be curved easier?
Harry

[J Morgan]

Tearing the silkspan allows it to blend much easier than a cut. A cut line will show much more. Only time I use cut silkspan is when I'm trying to emulate panel lines with it.

J

[Surly_Schmidt]

With WBPU, I have tried tissue, brown paper, butcher paper and glass fibre. All work well. With the paper prducts I first wet the dull side then lay that onto the surface to be finished, shiny side looking at you, and use a CC to squeegy. Then lift paper and use brush to work well into foam. Reapply paper starting from middle and ensure no air bubble develop. I have vac bagged some which leasves an excellent finish.

[usmc_VTOL_mech]

This one is done with silkspan and poly
except for the engine naccelles...those were done with 3/4 oz fiberglass
If your careful and take your time you will get a minimum of wrinkles

[GNieuwoudt]

Can some one explain what Poly C is. What type of glue is this.
Thanks
Gert

[Water Boy]

GN, WBPU or Poly C is Water Based Polyurethane or Polycrylic. Its used as a wood stain or sealer. But for us we use it for fiber glassing and coating our painted models. The main type is made by Min Wax and can be found at almost any home improvment center and wallyworld.

[HAWK3Y3]

I am currently building a GWS P-38. I filled the molded panel lines with light weight spackle and sanded smooth. I then applied a coat of WBPU. I took a piece of newspaper and wet both sides with WBPU and applied to the foam. It forms to compound curves well when soaked and wrinkles are worked out with a quick rub of my finger. I lightly sand the newspaper to knock down the high spots and then apply another coat of WPBU. Another quick sand and a coat of primer is laid down. Sand again, then a coat of flat black paint is applied. Sand again, apply another coat of flat black. I then sprayed a thin coat of chrome. The chrome shows every imperfection. Looks good, cheap, and seems to hold up well. I will post photos shortly. This is the first time I have used the newspaper and WBPU combination to cover the entire airplane. Not sure how weight compares to fiberglass and WBPU.

[Chris F]

How much weight do you think the newspaper, wbpu and paint has added? I'm looking forward to the pics, it sounds good!

[HAWK3Y3]

I don't have a scale but the additional weight is very noticable. The wind is quite strong here in Norfolk, VA. I am hoping the additional weight will not be noticed since I am running two Eflight 400 inrunner brushless (geared 5.33:1) and three bladed 9x7 props.

[Chris F]

I did it!

Here are some pics I took during the process and the finished product. Thanks for all the advice I got and J Morgan, I teared the Silkspan in some places but I used scissors on the wing tips and sanded smooth after.

For a more detailed version of the method check my blog here
http://www.rcgroups.com/forums/showthread.php?t=822103

[D_FAST]

Ive used the newsprint and wbpa.

I used 3m77 on mine then coated and sanded with wbpa. Turns out real nice. And like other covering techniques, any paint can be applied afterwards. More in depth look can be found here.

http://www.rcgroups.com/forums/showthread.php?t=561587&page=97

[GotrekGurnisson]

If you are using paper (newspaper, brown paper, crepe paper, etc) then instead of WBPU you can use watered down PVA (white wood working glue). Seal when down with a coat of WBPU. There are a few threads scattered around the forum that cover brown papering this way.

[gibb83]

ive bought some poly-c and tissue paper from rcworld.co.uk. the tissue paper is 4g and 8g. this seems almost three times lighter (or less?) than some silk i bought at the local dress store.
i wonder how strong the tissue paper is compared to the silk, as it seems quite delicate.
ive got a ultrafly su-27 to cover and maybe it needs the stronger stuff, but weight is always an issue. could be my silk isnt appropriate for the job, too heavy, but then again, when im doing the covering job it should last a few mistakes..
does anyone know how to calculate/guess the auw after covering?
thanks

[Jacques.Eloff]

ive bought some poly-c and tissue paper from rcworld.co.uk. the tissue paper is 4g and 8g. this seems almost three times lighter (or less?) than some silk i bought at the local dress store.
i wonder how strong the tissue paper is compared to the silk, as it seems quite delicate.
ive got a ultrafly su-27 to cover and maybe it needs the stronger stuff, but weight is always an issue. could be my silk isnt appropriate for the job, too heavy, but then again, when im doing the covering job it should last a few mistakes..
does anyone know how to calculate/guess the auw after covering?
thanks

I’m considering using Matt Halton’s idea of tissue and Poly-C for my Fly Fly BAE Hawk EDF. I was also keen to find out the weight penalty, so decided to do some weight tests on a mock up. After struggling to find some foam blanks, decided to use a piece of foam from the packaging for my TX. I cut/shaped it to roughly 11 x 20cm and it is about 1.5cm thick (total 530cm2).

Results are as follows:
Starting mass: 6g
Applied lightweight filler to some intentional dents: total now 6.3g after sanding
Add tissue and first coat Poly-C, weight now up to 9g
Second coat Poly-C takes it up to 9.5g
Third coat takes it 9.9g
Fourth takes it to 10.5g
One coat of spray paint takes to 11.1g
I haven't put on second coat of paint, but guess it will be around 12g.

So, basically this sheet of foam has doubled in weight. If I extrapolate the weight/area ratio to the Hawk (which has around 20,000cm2 airframe surface area) I come to around 200g total weight penalty. It must be said that this is a fairly large EDF: 1465 length, 1365mm span with a fat/deep fuselage and it will probably be fine. But this does mean a lot more work.

[CRAZYDAVE]

Sorry to resurect a dead thread, but I have a few questions:

I tried to cover a wing in Minwax WBPU and tissue, but found it extremely difficult to remove all the wrinkles.

From what I read, you simply sand them out after it dries?

What grain sandpaper do ya'll use for the final sanding? Is 280 too coarse?

I'm worried about adding all the extra weight to my model, a GWS Spitfire.

[suirendoujin]

Am currently working on a Windrider BD-5 as a sloper. Gave third coat of WBPU to the whole airframe. Shiney, clear. Would prefer a more CRISP surface, but!!!! I am enjoying this process none the less. Smooth surface obtained through family friendly protocol.