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Spiral filling experiment

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kjkcolorado

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Many threads here on TRF discussing filling body tube spirals. Previously I’ve used Elmer’s Carpenters Wood Filler (CWF) and Bondo Glazing and Spot Putty (Bondo). I had two full lengths of 38mm Blue Tube and a full length of 38mm Blue Tube coupler in my rocketry parts stash and decided to do a little test. I used CWF thinned to a mustard-like consistency on one, Bondo on another, and finally BSI 30 min epoxy on the last. Normally I don’t fill spirals on couplers, but did for the sake of this activity. Both the CWF and Bondo could be done in one sitting. This is the first time I have tried any type of epoxy to fill spirals and did it in two sittings to keep from making a mess with drips (layed tube horizontal and did top half one day, flipped and did the other half the next day). After drying, all tubes were rough sanded with 100 grit to get the major overfill off, then 220 and finally 400 to smooth them out completely.

Immediately after this sanding process I could feel a slight indentation on the spirals filled with the Bondo. For a perfect finish, I would definitely need to do another coat of Bondo and/or use multiple coats and sanding with a filler/primer. I have done this previously. With the CWF I could also feel a slight indent with my fingernail. It was not as pronounced as the Bondo, but still noticeable. The epoxy filled spirals were perfect in my estimation. Could not feel any texture change going over the spirals, and I tried hard to find some.

So, all these tubes are still sitting around a few weeks later. I took a good look and feel of them again today. The Bondo has shrunk/contracted a little more and the indentations are even more pronounced. The CWF seems about the same. Epoxy still great. With two prior builds using the Bondo method, even after a second Bondo coat then priming and painting I have had visible spirals seem to show up several months later. Note sure if anyone else has seen this. I do live in a very low humidity region (Colorado) and wonder if this effect is pronounced because of that.

In terms of application, the Bondo took the least amount of time and effort. Right out of the tube and rubbed into the spiral. CWF was second easiest. After thinning, ‘paint’ along the spirals. As I mentioned, the epoxy took two sittings and was the slowest to apply. I used a bambo kabob skewer to drag it into the spiral. However, given the results, this will be my new favorite method.
 

solid_fuel

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in active time, prep, mixing/thinning, applying and sanding, if you were to do two sittings of CWF vs the epoxy which takes more time?
 

kjkcolorado

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Two applications of CWF would still be faster. Once mixed it goes on really fast with a cheap hobby paint brush. ‘Dragging’ the epoxy through the spiral groove like I did with a bamboo skewer was a bit tedious. The BSI 30 minute epoxy is pretty runny right after mixing and I bet it would be pretty easy to apply it with the same type of brush. I used the bamboo skewer because it was what I used to mix up the small batch of epoxy. Also I don’t want to have to clean epoxy off of or throw out my small brushes (even though they’re cheap).
 

bjphoenix

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I tried my hand at filling the big spirals in an old phenolic tube. I had read about epoxy putty so I used some JB Weld wood filler that I had on hand. It takes a good amount of time to push the putty into the spirals and cut off the excess with a single edge razor blade. After curing I sanded the tube. I saw little imperfections in the putty so I then put on a layer of CWF. I sanded that off with 220 grit. I could still feel indentations after that. I sprayed on some primer to have a look and the indentations aren't bad. A few coats of primer might make them acceptable but still not what I expected after all that work.
 

kjkcolorado

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I’m willing to put more effort/time in up front if it saves on finishing later. It will be a while until I get to my next build and use this tube filled with epoxy. I’m anxious to see what it looks and feels like after a single primer coat.
 

BA_Incognito

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The best thing I have found is the Rust-oluem "2 in 1 Filler and Sandable Primer" Its in the automotive section. Spray the body tube with a coat or two, then sand down. Since the primer is a bit thicker than usual, it fills in the spirals nicely.

primer can.jpg bt sanded.jpg
 

Trident

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I too like the Rustoleum 2-in-1 Filler and Sandable Primer. I’ve found it on sale for a little over $3 per can on Walmart.com. Free shipping to your store, too. I’ve not checked in a few months since I bought 6 cans the last time. The prices can vary so you have to monitor the site for when it goes on sale.

My favorite primer is Duplicolor, but it costs a lot more.
 

bjphoenix

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My father used to own a garage and body shop- I seem to remember that Bondo polyester body plastic would shrink with long term curing. I'm not so sure about the glazing putty but I think it would all shrink a little bit. For automotive use you end up with sometimes 3 or 4 coats of filler and multiple coats of primer, probably partly to compensate for the shrinkage of the material. I don't know that the amount in the spiral groove of a phenolic tube would be enough to shrink a noticeable amount.
 

Trident

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The Bondo Spot and Glazing Putty will crack if put on too thick. I don’t use it for filling seams. (I’m lazy and just fill them up with primer coats.)
But I do use it for touching up fillets, for filling in small voids or to even things up.
 

heada

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I use 30 min epoxy (cheapest stuff I can find) add enough microballons to it so that its the consistency of thick peanut butter. I want more macroballons than epoxy in the mix. Fills the spirals, sands quickly and easily and doesn't shrink.
 

Marc_G

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For shallow spirals a good filler I use is Brodak sealer amended with a bunch of talc for thickening. Dries quickly, easily sandable, works fine under all paints and primers I use.

This is my go to for Kraft paper tube spirals and would also work well for light to moderate spirals on the heavier tubes you discussed.
 

kjkcolorado

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My favorite is SuperFil, which you can buy from Aircraft Spruce.
I like hearing about the other products people have used for this as I am still searching for something I like better. Question about the Poly-Fiber Super Fil. The description says it is an epoxy. Other than it looks to be lighter weight, any other advantages over the cheaper BSI 30 min epoxy?
 

Steve Shannon

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I use 30 min epoxy (cheapest stuff I can find) add enough microballons to it so that its the consistency of thick peanut butter. I want more macroballons than epoxy in the mix. Fills the spirals, sands quickly and easily and doesn't shrink.
That’s as easy as it gets, a cost effective substitute for Superfil.
Darrell Mobley used Killz primer. Put it on thick and sand smooth.
Personally I use CWF for small projects and fiberglass cloth for big ones.
 

mccordmw

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I simply use regular old CWF. I don't need to thin it. Just put on a blob and scrape it down the grooves with an old plastic card. No need to get fancy.
 

cwbullet

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That’s as easy as it gets, a cost effective substitute for Superfil.
Darrell Mobley used Killz primer. Put it on thick and sand smooth.
Personally I use CWF for small projects and fiberglass cloth for big ones.
CWF is my first choice too. I often add a little water and paint it on.
 

Jozef

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Immediately after this sanding process I could feel a slight indentation on the spirals filled with the Bondo. For a perfect finish, I would definitely need to do another coat of Bondo and/or use multiple coats and sanding with a filler/primer.

Try using a single edge razor blade or shard edge plastic card to apply bond glazing putty or CWF. I do the entire tube... not just spirals. Cardboard airframes have a lot of surface irregularities. Allow the bondo to dry several days before block sanding. It is a solvent based product and will shrink over time. If it has a strong odor, it is not ready too sand. Blck sanded left, post application right.

IMG_3807.JPG
 

JohnCoker

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I like hearing about the other products people have used for this as I am still searching for something I like better. Question about the Poly-Fiber Super Fil. The description says it is an epoxy. Other than it looks to be lighter weight, any other advantages over the cheaper BSI 30 min epoxy?
Yes, it is an epoxy, but light weight and easily sandable. (It's much less dense than any bonding or laminating epoxy.)
 

grouch

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I use Super Fil on nose cones for the same reason. Easy to sand and it sticks to the weird LOC cones like hair on soap.
 

JERRYR708

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Two applications of CWF would still be faster. Once mixed it goes on really fast with a cheap hobby paint brush. ‘Dragging’ the epoxy through the spiral groove like I did with a bamboo skewer was a bit tedious. The BSI 30 minute epoxy is pretty runny right after mixing and I bet it would be pretty easy to apply it with the same type of brush. I used the bamboo skewer because it was what I used to mix up the small batch of epoxy. Also I don’t want to have to clean epoxy off of or throw out my small brushes (even though they’re cheap).
I mix micro balloons into the BSI epoxy to thicken it up so it doesn't run and it makes sanding much easier.
 

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