What are you guys using to fill gaps in foam ? - RC Groups
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Jun 21, 2002, 04:54 PM
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What are you guys using to fill gaps in foam ?

I was wondering what stuff I could use to fill smal gaps in foam structure of my tipsy (wing and fuselage).

Something light that is easily sandable...

What about Elmer's Pro Bond ?

My father told my to use Polyfilla... yeah right, the old man is not into RC that much. My Tipsy would be 20lbs if I listened to him...

Thanks for the tips !

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Jun 21, 2002, 05:05 PM
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member73's Avatar
In my experience, I haven't found ProBond to be that easy to sand. Its much harder than the foam, so its difficult to get a nice flush finish. If you have a local hobby store nearby, get a tub of balsa filler (Hobbylity is Hobbico's version, there are several others). Very light weight, dries fairly quick and no harder to sand then most foams. If a LHS is not available, you can find light weight spackle at the hardware store. Not sure of the relative densities since I've never used the stuff, but I see it suggested here quite often and since everyone here is interested in every last gram, it must be pretty close. If you need a structural joint, mix microballons (available at the LHS) with epoxy to make a lightweight but strong filler. The microballons also make the epoxy a lot easier to sand.

Best of luck!
Jun 21, 2002, 05:17 PM
Registered User

I've found that the very best filler material is none at all. I haven't found any filler that matches the texture of any of the foams. So, after filling and sanding, I have a more noticable seam or spot than I did before! Paint won't cover the textural differences. The only exception I can think of is if you planned to use a covering material like monocote after filling and sanding. Sometimes doing nothing is best.

Jun 21, 2002, 07:17 PM
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poobs's Avatar
Light weight spakle from the hardware store. It feels like the can is empty when you buy it.
True that when you sand it it will not hae the granular testure of the foam.
Jun 21, 2002, 08:20 PM
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mefly2's Avatar
I haven't tried LW spackle on foam, but I do know it works great on balsa. The only problem is that the white will show through some coverings. I have had good luck using food coloring(yes, food coloring) like for coloring frosting for cakes. You can make the spackle any color you want by mixing the colors together. Just don't use to much...this stuff is very concentrated so a little goes a long way. I think you could make the spackling the same color or close as your plane, and it would look pretty good with out covering over it.
Jun 21, 2002, 08:26 PM
Registered User
I like probond for glueing foam....it fills in a little, but is very hard.

Has anyone ever tried that "foam-in-a-can" insulating stuff that is used for household applications? It is starts out as a goo out of the can, and quickly expands/dries into a light foam material.
Jun 21, 2002, 09:57 PM
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mtayl's Avatar
I found probond to be an extreme pain to sand if it had foamed up a lot. Several people have said that once you put it on to take some strapping tape and lay it down hard where the probond is. This should keep the foaming action going into the wing instead of on the wing. I have to probond some CF mounts tonight so I'm going to try this and see how well it works.