Getting a Good Finish - Filler Primer Spray vs Diluted Wood Filler?

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

wyattjohnson35

Well-Known Member
Joined
May 25, 2018
Messages
54
Reaction score
3
I was wondering what the best method is to cover up the spirals on body tubes and the indentations on fins and nosecones? I'm using Painter's Touch Filler Primer, 3 coats, with sanding to achieve a smooth look, but I also have materials on hand to do a 1:2.5 dilution of water:Minwax Wood Filler and I'm wondering which gives a better "liquid metal" type finish ? Can I use the wood filler on the body tubes to cover spirals as well as the nosecone? What amount of sanding is recommended to get a "liquid metal" finish?
 
A summary of Chris Michielssen's techniques are given on the NAR website. You can also search his blog for lots more info. His techniques are pretty representative of what many of us do (in some cases, at least, because we learned it from his blog :)).

Anyway, there are *many* ways to tackle this. In general, filler/primer is a good final step. In some cases, filler/primer may be all you need, although it could take several coats. I haven't used the Minwax Wood Filler; most of us typically use Elmer's *plain* Carpenter's Wood Filler (aka CWF), very slightly diluted to get a mustard-like consistency.

Personally, for my fins I've settled on papering with Avery label paper (described many times throughout these forums) as my preferred technique, finished with filler primer.

For balsa nose cones, I typically apply CA and sand down to get a hard shell, then finish with a layer of thinned CWF and filler/primer.

Any of these techniques will get you a sufficiently smooth base for your paint. Ultimately getting super-gloss finish becomes dependent on laying down good coats of paint, which is a whole other issue. :)
 
I've yet to try it on a rocket, but I will tell you how I got a good, smooth base on balsa hand-launch gliders......find some white styrofoam and dissolve it in dope, butyrate dope used for covering stick and tissue models. You will have to play with the mix, but start with about a half-pint in an old glass jar, and add the styro. Stir it til it is a thick but smooth mixture, think pancake batter. paint it on, sand smooth and repeat if necessary. It dries and forms a styrene surface that is waterproof, dent resistant and takes Krylon or Rustoleum very well!
 
I've yet to try it on a rocket, but I will tell you how I got a good, smooth base on balsa hand-launch gliders......find some white styrofoam and dissolve it in dope, butyrate dope used for covering stick and tissue models. You will have to play with the mix, but start with about a half-pint in an old glass jar, and add the styro. Stir it til it is a thick but smooth mixture, think pancake batter. paint it on, sand smooth and repeat if necessary. It dries and forms a styrene surface that is waterproof, dent resistant and takes Krylon or Rustoleum very well!

That sounds like a formula I found on the web for homemade sanding sealer. It's just two ingredients: Styrofoam and MEK ( methyl ethyl ketone), a solvent. Much cheaper than commercial sanding sealers. Seals the wood like liquid plastic. Usually one or two coats will do the job. Use a disposable brush and work in a well ventilated area, breathing in the fumes can give you brain damage long term. I use the Styrofoam peanuts that come with my rocketry mail orders, it dissolves instantly in the MEK. Store in a glass jar, careful what kind of gasket you use on the jar as it can dissolve many synthetic rubber gaskets.

Here's the link:https://fdsailor.blogspot.com/2011/08/how-to-make-sanding-sealer.html
 
MEK works, too. I've always used dope simply because that is what I have on hand. I also think the dope helps the styrene to penetrate into the wood grain better. I'm a retread into rocketry, have been sealing balsa fins with tissue and cyanacrylate followed by gray automotive primer. Need to give the old styro trick a try on my next build
 
We used to mix baby powder in clear dope for sanding sealer. It seemed to me that the "normal" (SIG) sanding sealer was sawdust in clear dope. Something a bit easier on the nose is using water-based poly with baby powder.
 
All the above methods are fine, but just to be clear you don't need to do a chemistry project to accomplish your objective here. Simple water-based CWF finished off with filler/primer works fine, and I think is particularly ideal for spiral-filling. It also works for fins an nose cones, although as I said I like to do a CA soak on nose cones first, and then finish with CWF and filler/primer (and paper on fins).

If you want a more traditional sanding sealer, then Brodak seems to be the best source nowadays.
 
I use Deft Laquer Sanding Sealer, on the shelf at the usual hardware stores. May take more coats than Brodak, but cheaper, so take your pick. It works well on balsa, and can fill spirals on body tubes also, more like a pre-primer coat.

Regardless of the sealer you choose, you might consider sanding with fine then very fine paper, like 200 then 400 grit as you progress. You can even use 0000 Steel Wool if you don't mind the mess.
 
For plastic nose cone mould seams, I use CWF to fill then sand, and then wick thin CA into the CWF and sand again.

Tough, light, and hard as nails...

And +1 for papering fins... I use thin CA on the edges to seal, tough as anything (I’ve had Mach flights with papered balsa fins with CA edges and epoxy fillets)
 
Back
Top