Newbie here with a question about finishing balsa fins

[P-40Warhawk]

Hello folks,

I just joined the forum and have a question about finishing balsa fins. First, I want to apologize if this has been covered before but I did search the forums but failed to find the answer I'm looking for.

I was an avid builder of Estes and Centuri rockets in the 70's as a kid (how I wish some of those old kits, such as Estes's Gemini Titan, would reappear, but I'll leave that post for another day!). I've recently started to get back into rockets and started working on the Estes V2.

I did not have handy either Aerogloss balsa fillercoat or Aerogloss sanding sealer (my "local" hobby store isn't too local) for the balsa fins so instead picked up some sanding sealer at the local Home Depot. Unfortunately, all it had was Miniwax, a water-based sealer. Fortunately, I did search this forum and was prepared (somewhat) when the fins started to warp so minimized it.

Now on to my question: I've put two coats of Miniwax sanding sealer on the fins, sanding between and after the coats. The fins are not yet filled or smooth to my satisfaction. Should I keep using the Miniwax sanding sealer and hope there's no more warpage? Or can I switch to a lacquer-based sanding sealer (such as Aerogloss) at this point? I did pick up a bottle of Aerogloss balsa fillercoat, but it appears this should be applied before and not after the sanding sealer.

TIA for taking the time to read and respond to my post!

(Forgot to mention that, even if an option, I would prefer not to paper the fins!)

Mark

 

[samb]

Welcome back P-40.

Did your HD have Elmers Carpenter's Wood Filler ? https://www.elmers.com/product/detail/E848D13?filterPath=wood-filler

That's what I use, the trick to minimizing/avoiding warpage is to mix it with right amount of water and no more. Hans Michielssen has what you might call a "content rich" site concerning all things model rocketry and here is his page in working with CWF: https://modelrocketbuilding.blogspot.com/2010/09/carpenters-wood-filler-mix-ratios.html
Highly recommended stuff in there, thank you Mr. Michielssen !

My local HobbyLobby carries the Aerogloss products. If you have one of those available check it out.

I suspect you'll get many answers to this question as we're all on a never ending quest for the perfect filler.

 

[luke strawwalker]

My advice-- dump that junk (both the minwax crap and the aerogloss) and go one of two ways...

1) Paper the fins... Here's some threads where I discuss techniques, with pictures showing how to do it... https://www.rocketryforum.com/showthread.php?13600-Dr-Zooch-Vanguard-Eagle-Beta-Build-Thread
(specifically posts 6,7,8, and 9)

https://www.rocketryforum.com/showt...-papering-techniques-I-m-still-not-sold-on-it!

https://www.rocketryforum.com/showthread.php?42250-Balsa-technique-question

https://www.rocketryforum.com/showthread.php?41698-help-with-papering

https://www.rocketryforum.com/showthread.php?40256-Balsa-to-Super-Smooth-Putty-vs-Sanding-Sealer-vs

https://www.rocketryforum.com/showthread.php?38369-Papering-fins

https://www.rocketryforum.com/showthread.php?35155-Balsa-fins-filler-primer-versus-paper

https://www.rocketryforum.com/showthread.php?32708-How-do-you-paper-fins-to-make-them-stronger

https://www.rocketryforum.com/showthread.php?30957-Newby-techniques-please

https://www.rocketryforum.com/showthread.php?28632-Paperen-Fins

https://www.rocketryforum.com/showthread.php?13933-TLP-Maverick-build-thread


2) Get some Elmer's Carpenter's Wood Filler from the local indoor lumberyard or hardware store... you want the SMOOTH kind, not the grainy stuff (think the grainy stuff is labeled "sandable wood filler" or something-- it's VERY gritty and somewhat darker, and has glass beads in it... it's TERRIBLE... about like sanding rocks-- look for the "creamy" stuff that looks like peanut butter-- it's usually in a white tub with an orange lid and blue label marked "carpenters wood filler").

Take a dollop of that stuff and put it in a baby food jar, or one of those little snap-on lid type containers like you'd get your side item in at KFC, or whatever is similar... (resealable plastic cup, basically). Using a 1 inch wide paintbrush, add a few drops of water, and "tapping" the dollop of filler with the paint brush, work the water into the dollop of filler... add a few drops of water at a time until the thing totally dissolves and you end up with something the consistency of HOT DOG MUSTARD... then brush that on your balsa parts, DOING BOTH SIDES AT ONCE, allow to dry a few hours or overnight, and sand with 220 grit sandpaper followed by 400 grit wet/dry.

https://www.rocketryforum.com/showthread.php?12267-Question-about-using-Elmer-s-Fill-n-Finish

https://www.rocketryforum.com/showthread.php?7719-Elmer-s-Carpenter-s-Wood-Filler

Also, you REALLY want to be using DOUBLE GLUE JOINTS to attach your fins... Pics and details on post 26 in this thread:

https://www.rocketryforum.com/showthread.php?29228-Dr-Zooch-Rockets-EFT-1-beta-build

More details/pics in post 12 of this thread:

https://www.rocketryforum.com/showthread.php?25443-Dr-Zooch-SLS-beta-build-thread

and post 45 of this thread:

https://www.rocketryforum.com/showt...nniversary-Dr-Zooch-Mercury-Atlas-build/page2

https://www.rocketryforum.com/showt...-To-Flight-Space-Shuttle-build-thread-2/page2

https://www.rocketryforum.com/showthread.php?47950-Fin-Glueing-Guide

https://www.rocketryforum.com/showt...d-for-Cape-Canaveral-Air-Force-Station-Museum!

And you want to get something called "Titebond Moulding and Trim Glue" or "Titebond Moulding and Trim Wood Glue" at the big hardware store while you're there... stuff makes PERFECT fillets on rockets-- no muss, no fuss... best stuff I've found bar none...

https://www.rocketryforum.com/showthread.php?31726-Titebond-Glue-Anything-NOT-to-use-it-for

https://www.rocketryforum.com/showthread.php?4439-Dr-Zooch-Saturn-V
Works like a million bucks!

Later and good luck! OL JR

 

[samb]

... Now on to my question: I've put two coats of Miniwax sanding sealer on the fins, sanding between and after the coats. The fins are not yet filled or smooth to my satisfaction. Should I keep using the Miniwax sanding sealer and hope there's no more warpage? Or can I switch to a lacquer-based sanding sealer (such as Aerogloss) at this point? I did pick up a bottle of Aerogloss balsa fillercoat, but it appears this should be applied before and not after the sanding sealer.

...

Mark

Some thoughts on your specific question:

Here's what I would do on the V2: after sanding the fins to your satisfaction, I'd hit them with a scratch coat of Rustoleum filler/primer, https://www.walmart.com/ip/Rust-Oleum-Filler-Primer/16816077 ,or your primer of choice. The remaining imperfections will really pop.

Commence to sanding down the primer with 400 grit paper

If any deep grain remains, I'd fill them the Elmers wood filler and commence to sand those area lightly (after the filler dries of course)

Another coat of primer, then more sanding; then ... you make the call ... good enough ? or more filling/priming/sanding ?

 

[P-40Warhawk]

Thanks for the input Luke and samb; I really appreciate your replies. For now, I'll give the primer and Elmer's wood filler a shot and go from there. By chance, I stopped by the local Home Depot today on the way home from work and picked up some of the Elmer's wood filler. I actually got it because I was looking for Fill 'N Finish, which from these forums I learned would be of good use to fill the seams in the body tube (something I never did or even knew about in my youth). I couldn't find the Fill 'N Finish but assumed the wood filler was the next best thing, and apparently it's actually the same thing with only a new name, according to Chris Michielssen's website.

From perusing these forums, it's obvious that things have change quite a bit in the 35 years or so when I was last into rocketry!

Mark

 

[luke strawwalker]

Thanks for the input Luke and samb; I really appreciate your replies. For now, I'll give the primer and Elmer's wood filler a shot and go from there. By chance, I stopped by the local Home Depot today on the way home from work and picked up some of the Elmer's wood filler. I actually got it because I was looking for Fill 'N Finish, which from these forums I learned would be of good use to fill the seams in the body tube (something I never did or even knew about in my youth). I couldn't find the Fill 'N Finish but assumed the wood filler was the next best thing, and apparently it's actually the same thing with only a new name, according to Chris Michielssen's website.

From perusing these forums, it's obvious that things have change quite a bit in the 35 years or so when I was last into rocketry!

Mark

You're welcome...

Yes, things have changed remarkably-- I sorta drifted out of rocketry when I graduated HS in 89... was gone more or less until about 2004 or thereabouts... AMAZING how much stuff has come in during that 15 years I was gone... and almost as amazing how much stuff has come and gone in the nearly 10 years I've been back...

Later and good luck with your projects! OL JR

PS. more specific to your situation, depending on how bad the fins look, you COULD Just give them several good coats of primer and then let that cure well (maybe a day) and sand them down... start with 220 grit, let the paper do the work (don't press hard-- it just heats up the primer, makes it gummy, and ruins the paper) and see how it looks... If it's pretty close to good, give it a couple more good shots of primer and sand it again... maybe hit it again if it looks necessary...

Another good material you might take a look at before you primer anything, if the grain is still pretty visible... Bondo Glazing and Spot Putty... There's a thread around here where we've been discussing that over the last few days... that is THE best stuff to fill tube spirals and get rid of them IMHO, out of everything I've tried. You don't USUALLY use it on fins, and it doesn't play well with enamel primers because it uses lacquer thinner as a carrier (which it too 'hot' a solvent for enamels and will crinkle or lift them) but if you use it on bare tube or bare wood, it's pretty good. Especially since you've already put this minwax stuff on... (but you might want to check a small area and do a "test" first, to make sure it doesn't go wonky with the minwax junk... never can tell-- always better to do a 'compatibility test' than find out by having to sand everything out to a clean start again).

The Bondo Glazing and Spot Putty is used for autobody finishing, to float out the final imperfections after applying and sanding Bondo body filler on cars... it's a thick, red putty with just enough lacquer thinner to make it about the consistency of toothpaste. You can buy it in various size toothpaste like tubes at the auto supply stores or WallyWorld...

Later! OL JR

 

[samb]

... it's obvious that things have change quite a bit in the 35 years or so when I was last into rocketry!

Mark

Yes, things have changed remarkably-- I sorta drifted out of rocketry when I graduated HS in 89... was gone more or less until about 2004 or thereabouts... AMAZING how much stuff has come in during that 15 years I was gone...
...
The Bondo Glazing and Spot Putty is used for autobody finishing, to float out the final imperfections after applying and sanding Bondo body filler on cars... it's a thick, red putty with just enough lacquer thinner to make it about the consistency of toothpaste. You can buy it in various size toothpaste like tubes at the auto supply stores or WallyWorld...

30+ is the magic number. My hiatus was from '74' till 2006. And JR is right, Bondo Spot Putty is in the kit at well. Lots of stuff available so try it all and find out what works best for you.

 

[Handeman]

I've tried a lot of different techniques for getting smooth balsa fins over the years. I've pretty much given up on fillers since I found the Filler Primer that samb mentioned. It is thick and fills in very well. The secret it to sand the balsa smooth first, then sand the primer completely off the high spots so just the grains/low spots are filled. Do this 2 or 3 times. Then just sand the last coat smooth but not enough to have any balsa showing through. The finer the sand paper you use, the longer you have to wait before sanding to keep it from gumming up the sandpaper. I usually wait overnight between coats.

I use the same technique to fill the spirals on the tubes. You can put several coats of primer on, every 15 - 20 minutes, and make them pretty thick coats to fill the spirals. Wait overnight and sand it down until the tube is showing through at all the high spots leaving the thick primer to fill the spirals. It takes a lot of sanding to get all that thick primer off the high spots and leveled out with what is in the spirals, but 220 paper will go pretty quick. The final thin coat that doesn't expose any of the tube is done with 400 and/or 600.

Wet sanding will make the sand paper last much longer and give you a smoother finish and you don't have to wait for the primer to dry as long. You can wet sand in an hour. I do not recommend wet sanding if there is any balsa or cardboard exposed at all. The water will be absorbed, the fibers swell, and you end up with a mess. If you catch it quick, dry the part, and wait 24 hours for it to dry, and you can usually recover.

 

[P-40Warhawk]

Thanks again for the input. I'm familiar with the Bondo putty; I also build airplane models and have used the putty in some of those builds. Although I deal with plastic and resin for those models vs balsa and cardboard for rockets, it's becoming quickly obvious that some of the products and techniques are interchangeable with the two hobbies.

I'll pick up some of the Rust-Oleum filler primer from the local Wally's World. In the meantime, on one of the fins I sprayed a product called "Mr. Surfacer 500" that I had on hand and is probably similar to the Rust-Oleum product. It's also meant as a filler/primer and the results were pretty good, although I pretty much used up the remainder of that product on the one fin. The Rust-Oleum filler primer looks to be more easily obtained, and less expensive.

I have a bit more work on that one fin (along with the other three, of course!) to make it completely acceptable for me, but with the great suggestions all of you have given me I have no doubt that I'll have a V2 to be proud of when finished!

Thanks!

Mark