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Old Feb 13, 2009, 02:06 PM
warhead_71 is offline
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Both WBPU and ModPodge are water-based - so if your ink is water soluble it will "bleed"... you'll have bloody mess. I read somewhere to spray your printout with a fixative to protect the ink... but I'd test that before applying to your plane. The point of ModgePodge is to infuse the fibers of the paper and bond that to a surface. If you seal the paper, then the MP isn't going to infuse the paper. Printed paper decoupaged to your foam would be especially handy if you want to add lozenge patterns or "decals" like roundels, stripes, numbers and logos.
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Old Feb 13, 2009, 02:12 PM
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Darn I was in Lowes the other day picking up FFF, and there was a Michael's right next door. Next time I am near Michael's I will probably pick some up.
Old Feb 19, 2009, 11:38 PM
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I just used the "Hard Coat" on a new set of wheel pants for my Goshawk and it turned out pretty good.


I carved the wheel pants from laminations of 1/2" and 1/4" pink foam, then sanded them down with 60, 100, 150 grit sandpaper to get them smoothed out. The first coat of Mod Podge Hard Coat (MP-HC) went on as thin as I could get it then I let it dry. Same as the regular HP, the first coat dried with a bit of a texture to it... I think tiny bubbles form as the HP soaks into the foam. I sanded it lightly with the 150-grit to remove the texture, then the next coat went on much smoother. I put the parts in front of the heat vent so they'd dry quicker - about 10 minutes to dry per coat. Once dried, you can wet-sand using cold water and 200-grit wet sandpaper. I built up 4 light coats this way. The bottle says you can build up to 8 coats but I wanted to go sparingly to save weight... so I only did the 4 coats.

The finish is indeed much harder than the regular MP... it makes an audible "clicking" sound when I tap my fingernail on it. Not sure how durable it is until I crash it, but it feels substantial. The directions say it takes 24 hours to fully cure, so it might continue to harden overnight.

After the water evaporated from the final wet-sand, I went straight to spray-painting it. In all, from the first coat of MP-HC to paint took about 40 minutes.
Old Feb 20, 2009, 01:37 AM
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Those wheel pants look really good! Will you be using on the rest of the plane? Can you comment on the amount of weight added? Even if you don't have an exact figure I would be interested in hearing a rough estimate.
Old Feb 20, 2009, 01:39 AM
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I just looked at your pics of the full plane. That is very nice looking.
Old Feb 20, 2009, 01:45 AM
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The rest of the plane is already covered with WBPU (water-based polyurethane, for the uninitiated). I think the Mod Podge is lighter, dries quicker, and is easier to work with. The weight added with the MP is very negligible, but I didn't weigh before to see exactly how much it added.
Old Feb 20, 2009, 03:27 AM
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Sounds like all-around good stuff. I'll definitely give it a try.
Old Feb 20, 2009, 10:25 AM
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It's worth noting that neither WBPU nor MP gives a whole lot of structural integrity to the foam by themselves.... it just adds a protective coating to make the foam less prone to "hangar rash" and it seals the foam so you can spray-paint it without melting the foam. If you want a lot of strength, use tissue or newspaper or fiberglass cloth... something fibrous that will soak up the WBPU or MP and become rigid when dried. This will add a bit more weight, but a LOT of shear, tensile, and compressive strength.
Old Feb 20, 2009, 10:45 AM
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very good tips.

I'm very interested in trying this my self.

I really like the idea of adding sparkles. that would really look sharp with a nice paint job and a sunny day.


-JAY
(HobbySuperFreak)
Old Feb 20, 2009, 01:10 PM
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It makes a good glue, too. I've been using it to glue depron. Looks like it has many uses.
Old Mar 09, 2009, 08:21 PM
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I've got a plane I am almost ready to try this out on, but I was hoping to ask a couple more questions about your experience with it first.

I've decided that I want to try using MP with tissue paper on a belly lander. From what you have tried, do you think that the regular or hard MP would be better suited to a belly lander?

In the past, I've put a strip of strapping tape down the bottom of a belly lander. Do you think it would work to put a strip of the tape on and then put the tissue and MP over it? Do you think that the tissue/MP would be strong enough without tape?

I was thinking about options to help the drying time and ease of spreading. With the talk about thinning with water, and comparisons to acrylic medium, I was wondering if it could be thinned with rubbing alcohol the way that acrylic paints can. That would give easy thinning and faster drying if it worked. Have you tried that? I'm thinking I'll give it a try. Maybe after I get the layer with tissue down and sanded I could thin some out enough to airbrush on to get several fast thin coats. I know that some people do that with WBPU, but I realize this is a different medium and may require some experimentation.
Old Mar 09, 2009, 08:45 PM
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As a test, I tried the regular MP with newspaper and it is very stiff... just like a sheet of foam-core construction board.

I think it would be great for a lightweight belly lander. I'd do one coat on the foam, then the paper, then two more coats. For even more durability, add a second layer of paper. It doesn't add much weight but adds a lot of rigidity.

I have not tried the "hard coat" MP with tissue or paper. The hard MP I just put directly on the foam to seal it and give it a smooth hard shell for painting... but I think it might crack like an egg if you tried belly-landing on it. I'm sure it would be much better combined with tissue.

I'm not sure how well MP will adhere to the strapping tape... I have not tried going over it -- seems like it might not stick very well unless you sandpaper the tape first to give it some "tooth". I've had problems even getting paint to stick to some strapping tape.

I don't think you need to thin the MP... just work fast to spread the first coat very thin before it starts to set-up -- and don't worry if you don't get 100% coverage, you'll get it on the next round. The first coat you just want to get a bit of penetration into the foam. Sand the first coat once it dries before you add the paper... it will have a rough texture from air bubbles rising from the foam.

You really should test it on a scrap piece first to get the hang of how it spreads and how thick to put it on. It dries very quickly in front of a heat/wind source... I let mine dry by setting it in front of the heat vent. To soak your paper, put some MP in a plastic plate and drag your strips of paper through the puddlle as you squeegee the excess with a credit card or something similar.
Last edited by warhead_71; Mar 09, 2009 at 08:51 PM.
Old Mar 09, 2009, 09:38 PM
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Thanks for the advice! I'm thinking maybe I'll do news paper on the belly and the under side of the wings and use tissue paper on top. and sides of the fuselage. Sound like that would give me as much strength as the tape would.

Sounds like the hard coat MP is even stiffer than I had imagined. Definitely wouldn't want it to crack like an egg.

I'm expecting my plane to have an AUW of 14 oz before coating and painting. I'm hoping not to add more than 1.5 oz. I'll weigh it before and after and post how much it ends up adding. It may still take me a little while to get to it though. I've been really busy lately.
Old Mar 09, 2009, 10:13 PM
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Quote:
Originally Posted by iceburg47
Sounds like the hard coat MP is even stiffer than I had imagined. Definitely wouldn't want it to crack like an egg.
That's if you only use hcMP on foam with no paper at all. Because the hcMP gets hard and the foam is still flexible underneath, it wouldn't flex with the foam so it would crunch instead. But, with the addition of paper you'd get a much better result. The paper would give you a lot of shear strength that would prevent flexing.


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