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Old Jul 24, 2012, 09:47 AM
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United States, IA, Cedar Rapids
Joined Jun 2012
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Question
Reparing Styrofoam Heat Damage

How do I go about repairing visible heat damage in styrofoam?

While building this new plane I was heating up the metal main gear retract shield and pressing it into the styrofoam wing. I was doing this to recess the retracts. Well I got to close to the top wing surface and the styrofoam started to melt. The styrofoam did not fully melt but there are some holes and the individual styrofoam bits are now larger and hard. Is there something I can spread on top of this spot in the wing that will cover the damaged area and will accept paint?
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Old Jul 24, 2012, 10:38 AM
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rcav8r2's Avatar
United States, PA, Beaver
Joined Sep 2001
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Can you post a pic of the damage? A few different ways to fix this depending on how extensive the damage is.
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Old Jul 24, 2012, 01:32 PM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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There's no way to restore the old foam. The best option is to cut away the damaged area and glue in a replacement block of similar foam. Once dry slice and sand away the excess to match the curves of the surrounding area.

If the shape is still there but the heat just shrunk away the surface and left a shallow sort of damage then some of the ultralight wall filler compounds can be used to fill the area back up and then carefully sand to the original profile. Lay it in in thin layers and allow to dry fully. Pack in more than about 1/16 and the shrinkage will cause the filler to crack and pull away as it dries.
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Old Jul 24, 2012, 08:01 PM
I'm a pilot... 100 yrs to late
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USA, FL, Palm Harbor
Joined Jan 2005
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expanding foam would work as well. a small dab... let it expand, harden., easily cut and shaped to original outline but color issues since its yellow. Won't fall or chip out, etc
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Old Jul 26, 2012, 11:02 PM
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R Zielinski's Avatar
USA, NH, Madbury
Joined Dec 2007
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Quote:
Originally Posted by Thermalin View Post
expanding foam would work as well. a small dab... let it expand, harden., easily cut and shaped to original outline but color issues since its yellow. Won't fall or chip out, etc
Even less effort: find a piece of flat shiny flexible sheet plastic, preferably clear. (Old grocery cake lids and prepared food packaging lids work well). It should follow the curvature of the wing well. poke a few small holes in it to release the foam as it expands. I use Gorilla Glue white version. Stir in a few drops of water, paint it on the surface of the wing over the damage. Immediately tape the plastic sheet over it and seal the edges with clear tape or high tack masking tape.

The GG will foam up, excess will escape leaving easy to trim excess. Within 1 hour you can remove the plastic to reveal a perfectly shiny smooth patch that needs no shaping or sanding. The repair is tougher than the original and just about as light.
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Old Aug 16, 2012, 01:37 PM
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United States, IA, Cedar Rapids
Joined Jun 2012
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Finally got around to take a picture of the damaged area.
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Old Aug 18, 2012, 10:22 AM
Space Coast USA
hoppy's Avatar
Space Coast
Joined Oct 2000
21,007 Posts
No problem, fill with Light Weight Spackle, sand and paint with latex or any water based paint.

When using heat around foam I put a piece of thick cardboard over areas that might get fried.
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Old Aug 18, 2012, 11:03 PM
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United States, NC, Richlands
Joined Jun 2011
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Quote:
Originally Posted by R Zielinski View Post
Even less effort: find a piece of flat shiny flexible sheet plastic, preferably clear. (Old grocery cake lids and prepared food packaging lids work well). It should follow the curvature of the wing well. poke a few small holes in it to release the foam as it expands. I use Gorilla Glue white version. Stir in a few drops of water, paint it on the surface of the wing over the damage. Immediately tape the plastic sheet over it and seal the edges with clear tape or high tack masking tape.

The GG will foam up, excess will escape leaving easy to trim excess. Within 1 hour you can remove the plastic to reveal a perfectly shiny smooth patch that needs no shaping or sanding. The repair is tougher than the original and just about as light.
I use this method basically, white GG et al. Only I apply it, then spritz it with a small water spraybottle I use for the purpose & quickly cover it - wrapping the part if the option's available with wax paper strips I've pre-prepared in tape-like strips, as tightly as possible to help contain the GG once it starts to expand. Once wax papered I use multiple wide rubber bands to clamp down the wax paper, trying to get it to conform as much as possible to the original surface. Let it sit overnight, & remove the covering -- the GG won't stick to the wax paper, which comes off leaving a smooth filled surface behind.

One thing that'll help is to experiment with the GG first -- a little goes a l-o-n-g way; it expands more than you'll likely imagine. Put a dollop into a paper cup or such, hit it with the spritz & let it work overnight so you'll see how much it grows. Helps guesstimate how much you'll need. Overrun can be carefully sanded; too little can be topped off with another treatment. Main downside to the whole affair is the GG really yellows as time passes, & shows against the white foam. 'Course, there's treatments for that too -- that's why God gave us rattlecans.
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Old Aug 19, 2012, 08:01 AM
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USA, NH, Madbury
Joined Dec 2007
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Maybe just a false impression, but it seems to me that GG foams up even more if you stir a few drops or water in really well. (It doesn't really mix well, more of a slurry). I do this when looking for non-structural and light weight filling. It is so foamy, flexible and soft when it dries that I wonder about its structural strength in other (high stress situations). If I want to firmly bond two pieces together, I just wet the surfaces to avoid all the foaming, and hopefully get a stronger, less flexible bond. We should run some experiments on this, but that's been my experience.
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Old Aug 19, 2012, 11:06 AM
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United States, NC, Richlands
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The problem, if it can be called that, is you can't really "wet" EPO/EPP foam types - it just beads up on the surface. Packing the raw GG in w/o first spritzing just gives you a bit more time to get it into the crevises to anchor it well, & the after-spritz sort've slowly 'activates' it, givig time to cap it off with the wax paper. That's just the 'method' I learned & the way I've used it thus far - it's been really effective for repairing punched holes where you can't really get down in 'em well, which has been my most frequent need for it.

One other 'trick' is I mix the GG with small bits of foam I've trimmed off here & there (save it in a zip-lok). I feel that lightens the works & keeps things more like the original's consistency (resilience of the EPO/EPP) while also lessening the amount of GG required, limiting overexpansion. The OP of course isn't making the same type of repair, so I didn't mention that part. Again, that's just 'me' & 'my way'.....sharing for someone who might find it helpful. But yes, I strongly recommend experimenting with GG until you get an idea of what it will do -- good thought!
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Old Aug 19, 2012, 01:41 PM
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USA, NH, Madbury
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Quote:
Originally Posted by StarHopper44 View Post

One other 'trick' is I mix the GG with small bits of foam I've trimmed off here & there (save it in a zip-lok).
I like that idea, have to try it. But then again, I hope not to get holes that big!
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