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Old Dec 08, 2011, 09:02 AM
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Newspaper-glue covering improvement

IMO, this is an easier way to apply the newspaper-60/40 glue covering for foam.

1 - Lightly sand foam and wipe with IsoPropyl alcohol.
2 - Cover foam with a generous coat of 60/40 mixture of Elmers or Titebond glue and water.
3 - Pre-Cut paper to the correct shape and spray the paper with a light mist of water and apply to glued surface.
4 -.Deleted
5 - Squeegee the surface with a credit card to remove excess glue and smooth out wrinkles.
6.- Outer paper surface can be painted with a water based paint/primer.

Why use newsprint?
It provides a smooth surface, strengthens the foam and can be painted with any paint.
Unprinted newspaper can be obtained from U-Haul.

Additional Instructions:

#1 - Paper is much stronger in the cross page direction than in the vertical direction. Ever notice how you can tear newspaper very easily up and down the page. Trying to tear it in line with a sentence is much harder. The lesson here is to orient the paper strips so that the print runs in the same direction as the load on the surface. For instance, on a wing which wants to flex up and down, I'll run the paper with the sentences running parallel with the leading edge.
#2 The paper when wet will stretch to some degree but to make the surface as smooth as possible, use strips where there are complex curves.
#3 The glue is a mix of Titebond woodglue (60%) and 40% water. You can make it up in a large quantity and store it in an old oleo container.
#4 The paper is cut to shape before applying the glue.
#5 Apply a coat of glue to the foam surface. If it balls up, wipe it off, let it dry and sand it. The balling up is due to a greasy/dirty surface.
#6 There are 2 ways to do the next step.
----A. Using a spray bottle of water, wet both sides of the paper. Shake off any excess water and apply it to the foam surface.
----B. Apply the glue mix to one aide of the paper and spray the other side with water, then lay the paper glue side on the foam glue side. I think this way is a bit stronger.
#7 Smooth the paper down removing any wrinkles. Always use a credit card and squeegee any excess glue from the glue layer.
#8 On thin surfaces like a rudder, the paper must be applied to both the top and bottom at the same time to prevent the part from warping. The paper shrinks on drying.
#9 Sand the dried paper lightly with 400grit paper.
#10 Apply a coat of Polycrylic to all surfaces, sand, and use any paint you have for the final coat.

The best way to learn is to make up some test pieces and see how it goes. It makes the cheap $store foam ding resistance and adds a lot of stiffness. Try it on a 5x5 piece of polystyrene 6mm sheet.

Foam with and without paper covering. See this post for more strength tests.

A HINT FOR REPAIRS and COVERING SMALL AREAS

A neat way to do repairs or "bullet proof" a foam wingtip is to use Aleens Stretchable/Flexible glue and newspaper stock.
#1 - Cutout top and bottom paper pieces.
#2 - Clean foam with IPA or soap and water and allow to dry.
#3 - Moisten paper with a fine water mist.
#4 - Put a dab or two of the glue on the foam and spread around with your finger.
#5 - Apply the damp paper to the foam and smooth down with fingers and then squeegy with a credit card.
#6 - Repeat on bottom side.

This stuff is really sticky and holds the paper down real well. Sticks real good to your fingers also. It also has excellent adhesion to EPP and epolar(?) foam.
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Last edited by hoppy; Feb 11, 2014 at 08:27 AM. Reason: Updated procedure.
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Old Dec 08, 2011, 10:41 AM
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Big difference. Do you find the glue mixture better than WBPU? I know that it would be cheaper.

Tod
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Old Dec 08, 2011, 11:44 AM
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paper covering

I would like to hear more on this. I cover my wing leading edges with brown wraping paper installed wet, using 50/50 white glue. This gives a very strong leading edge. I fly in areas covered in gorse and rely on this to protect wings when I land out!!! It gives a very smooth surface for painting.
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Old Dec 08, 2011, 11:45 AM
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Good question - I used WBPU in the past but switched to Polycrylic. On my current build I've used Polycrylic, 50/50 Titebond with 50/50 covered paper/50/50 with wet paper/50/50 with dry paper. The 50/50 with the dry paper (water misted after application) is the least hassle and has good adhesion to the foam. Pulled off a nice even layer of foam when removed.

A coat of Polycrylic is applied after the 50/50 glue dries.

Brown paper works well but is heavier and stronger. I use it for areas like leading edges, etc.
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Old Dec 08, 2011, 12:12 PM
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I have used both with paper and I also have used very light shear polyester cloth instead of paper. In all cases when the applied material dries it tends to shrink. If you cover a large flat surface this shrinkage will warp the panel. I experienced this on the wing of a 200% Polaris water plane and tail feathers of any size. Anyone have experienced this and found a solution?

Oh and the 50 50 glue makes a harder surface when completely cured while the UBPU remains some what flexable so it depends on what you want the surface to be.
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Old Dec 08, 2011, 12:22 PM
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Have you weighed the resulting material? I'd like to know what kind of weight penalty I'm going to pay before trying this technique.
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Old Dec 08, 2011, 12:37 PM
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I have weighed, but can't remember for sure. Just like any other finish it depends on the person applying it. If done sparingly it might add 1.5oz per square foot or less. This isn't for a plane where weight is a major factor, but for one that you want to do a extra nice finish on. My Chubby Cubby build almost doubled in weight, but I used a lot of primer and paint on top to get a smooth glossy finish. You will be surprised how much weight finishings can add if you are not careful.
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Old Dec 08, 2011, 12:39 PM
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warping

I cover top and bottom together and this does seem to stop warping. If you have wing bowing, then this is a different problem?
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Old Dec 08, 2011, 12:44 PM
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Cover with paper in small sections, top and bottom, working from the root out towards the tip. This reduces the chance of warping due to shrinkage. Let each section dry before doing the next. The process takes longer, but makes a great, lightweight wing.
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Old Dec 08, 2011, 01:02 PM
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In my opinion both are from warping. I have tired covering top and bottom at the same time and find it to be hit or miss sometimes OK, but often no good. If you cover an aileron and when dried it looks like it is making a u-turn is that warping or bowing?

Quote:
Originally Posted by franciscan View Post
I cover top and bottom together and this does seem to stop warping. If you have wing bowing, then this is a different problem?
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Old Dec 08, 2011, 01:09 PM
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It's a bit ironic that paper covering is being considered here. Lots of builders have asked how to get the paper covering off Dollar Tree foam board, in order to save weight.

To each, his own.

Jim R.
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Old Dec 08, 2011, 01:16 PM
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3 problems with $tree foam paper covering:

1) it is a lot heaver than news paper
2) it comes off too easy
3) you can't do much shaping of the foam with it on

Flat parts would be OK till they get a little moisture on the paper.

So it's get rid of the bad and on with the good.
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Old Dec 08, 2011, 01:26 PM
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The new stuff for covering

I cover my foam wings and fuselages with Powertex fabric hardener. It is an environmentally friendly water-based alternative to polyester. Powertex hardener can be use materials like paper, cardboard and all absorbent materials, even fiberglass. Think about it, no more epoxy with fiberglass work. Plastic dont work with Powertex, they will not tact together. But that is only a good thing, because now you can do molds from plastic which has the "wax" on it self.

Powertex dries hard as a rock and after that it is water- and weather-proof. Powertex dries 3 weeks, that's only "bad" thing, if you are in hurry to build your project. Powertex comes with many different colours and transparent which is only "colour" which must be protected with a water-resistant varnish to become weather proof.

50/50 powertex and water works fine, the hardener result is allmost the same as using only Powertex it self (no water).

http://www.powertexcreations.com/

I also cover top and bottom of the wing together and it does not wrap at all. I think it will work fine with flat surfaces also. But why not put the foam and the covering under a pressure with plastic between the glued covering and the plate (plywood ect.) which has weights on it?
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Old Dec 08, 2011, 05:14 PM
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Quote:
I also cover top and bottom of the wing together and it does not wrap at all.
I can go along with that. Putting weights on a warped piece will straighten it out.
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Old Dec 08, 2011, 05:22 PM
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i have a half completed cub that i was covering this way. i too had warping that i couldnt seem to cure. did one side of the H stab, one side at a time, and it warped all out of shape. tried doing both sides of the other half at the same time... same result. i then tried to do the V stab both sides and jigged straight. once dry and removed from the jig it was still warped. I gave up and it now gets shuffled around under my work bench...
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