Sealing Balsa Fins?

[TangoJuliet]

I've made the switch from using AeroGloss Balsa Filler to the Brodak Balsa Sealer out of necessity due to AeroGloss no longer being manufactured. So far, I'm really pleased with the Brodak, but it is thicker than the AG. With AG I used to apply it after I'd glued my fins on, then lightly sand between coats. Since using the Brodak, I've found that it builds up more in the filets than I'd like, creating a larger radius.

Do you fill/seal your balsa fins after attaching them, or before you attach them to your BT? I think I may need to adjust my build process to start getting better results.

 

[K'Tesh]

I gave up on sealing for the most part, and have gone with papering.

 

[neil_w]

I'm all-in on papering as well, although I go the Avery label route.

 

[Micromeister]

I neither seal or paper balsa or basswood anymore.

Since discovering Cheap Auto primer seals and fills without the need for additional steps I've cut my construction prep time by about half without sacrificing quality or longevity of the finish. With well over 20 years using this procedure on more then 160 different rockets I just can't do it any other way.
Lack of transport and flight damage, and no lifting of papered edges lead me to concluded Liquid Fillers and/or the need to paper wooden parts are as unnecessary as using Estes always Way To Short Rubber shock cords.

 

[TangoJuliet]

I neither seal or paper balsa or basswood anymore.

Since discovering Cheap Auto primer seals and fills without the need for additional steps I've cut my construction prep time by about half without sacrificing quality or longevity of the finish. With well over 20 years using this procedure on more then 160 different rockets I just can't do it any other way.
Lack of transport and flight damage, and no lifting of papered edges lead me to concluded Liquid Fillers and/or the need to paper wooden parts are as unnecessary as using Estes always Way To Short Rubber shock cords.

And are you priming and sanding your fins while they are attached, or prior to?

I find it's been somewhat difficult to properly sand fins that are attached, but that's always the way I've done it. My underlying reason for this line of questioning is to improve my overall finish and build quality. I've been a modeler for a long time, but I think I need to change my processes in order to get to the next level. There's something missing... I just need to figure out what it is.

 

[neil_w]

And are you priming and sanding your fins while they are attached, or prior to?.

I had the same question.

The primer-only method sounds quite good, but just doesn't work for my situation because I have a somewhat overriding need to minimize the need for spraying.

 

[SCIGS30]

I think you will find that Brodak sealer produces better results than aerogloss. I usually seal my fins before attaching since it makes sanding much easier. I have never had a fin pop off but then I only build LPR.

 

[PatB]

I use FNF which doesn't really penetrate the surface, so I'm able to fill and sand the fins prior to gluing then on.

However, if you use some sort of dope that penetrates the surface pretty well then I'd glue the fins on first. I'd be concerned about the glue not soaking into a fin that has been saturated with dope.

 

[TangoJuliet]

I think you will find that Brodak sealer produces better results than aerogloss. I usually seal my fins before attaching since it makes sanding much easier. I have never had a fin pop off but then I only build LPR.

So far, I do really like the Brodak Sealer, but I did notice that when I applied multiple coats to attached fins that I got a significant build-up at the fillet that I didn't like. And in fact, on a recent Boost Glider I built, the build-up was so bad that there was a hollow void under it after it dried. Maybe I was applying it too heavy. I use an acid/epoxy brush to apply it.

 

[Micromeister]

And are you priming and sanding your fins while they are attached, or prior to?

I find it's been somewhat difficult to properly sand fins that are attached, but that's always the way I've done it. My underlying reason for this line of questioning is to improve my overall finish and build quality. I've been a modeler for a long time, but I think I need to change my processes in order to get to the next level. There's something missing... I just need to figure out what it is.

I almost always prime and sand After construction is complete or very nearly complete. I have on occasion primed and sanded fins for a couple Scale subjects before they are attached. This however creates another set of finishing problems and what to do about fillets if desired.

Sanding fins attached has always seemed to be the easiest way of getting the strongest attachments with or without fillets. Sanding fillets are generally done with a slightly finer grit sandpaper on a wrapping a dowel or similar object creating the proper and symmetric radii on all fins. I've used this technique for decades now on MPR, LPR and even Micro's.
As with any new or revisited technique there is always a learning curve to be considered. Glue fillets and primer only sealing/priming seems to take far less time getting used to then Fillers/Fillets/Priming and such
I'm not trying to say this is the only way to get good finishes, All I'm trying to point out is many of the Fillers or sealers leave more to be done then most any other technique. We all have to decide what and where to draw the line on time spent to finish quality. I've used many different techniques over the years and for my money "Primer over glue fillets" is by far the most time saving technique I've found to date.

I rarely use "through the wall" fin mounting for one very simple reason. When one has a mishap or hard landing snapping off a TTW fin is a major problem to correct.
I'd much rather snap off a fin at the root edge and be able to correct it, feather out the paint to the point the repair is invisible in a short time. I believe in Leaving TTW for the HPR folks, where TTW is really needed.
Hope these thoughts help a bit.

 

[hcmbanjo]

Over the years I've found I get a better finish if I fill and primer the parts before gluing onto the body tube.
This is just food for thought, do whatever works best for you.

https://modelrocketbuilding.blogspot.com/2017/04/why-do-i-fill-and-prime-before-assembly.html

First, I only do one brushed on coat of Elmer's Carpenter's Wood Filler and sanding. CWF is water based and doesn't seal the fin.
White or yellow glue will soak in when glue is applied.
Then one coat of Duplicolor primer/filler and sanding.
Sure, it's more expensive than the others but it only needs one coat (after the CWF) and one pass at sanding and the grain is gone.
So, one brushed coat of thinned CWF and sanding then one sprayed coat of filler/primer then sanding. Two sanded passes instead of four needed with sanding sealer or just the auto primer.
The Duplicolor Filler/primer does seal the surface so glue areas will need to be sanded down before gluing.

The first picture show the fin after the Duplicolor primer is sanded down. Note it is nearly removed near the root edge and fillet area.



This shows the root edge area primer/filler being sanded off.
I sand a little wider than the fin thickness for the fillets.



Note the mottled look of the grey primer/filler. After sanding it fills the last remaining
fin grain and body tube seams. White undercoats will follow before color coats.
I rarely have broken fins and they don't pop off the body tube.

 

[TangoJuliet]

Thanks Chris. I've perused your site several times. You do great work. I've tried the thinned CWF and didn't care much for it on balsa, though I do use it for spiral seams and a few other "gap filling" needs. Personal preference I guess.

I'm starting to get the feeling that I'm not sanding my fillers down quite enough, and perhaps not using the proper grit of sand papers when I do. I think what I'm seeing in my finishes is that the low spots that appear to unfilled wood grain is actually low spots in the filler coat(s), where the filler hasn't quite leveled out completely over the depressions. I'll experiment more with my filling/sanding techniques.

 

[SCIGS30]

For brushes I use Testors quality brushes and the work great for applying sealer, I can see where Expoxy brushes add too much sealer and harder to control. If I were building a showcase model I would build it and prime in sub assemblies like Chris does. Estes instructions now say to prime the rocket, sand, prime and paint. I have tried the primer only method and it works, but for me it took multiple coats and a lot more work than applying sanding sealer.

 

[TangoJuliet]

SCIGS30 - Are you cleaning your brushes afterward? With what?

 

[SCIGS30]

I use Brodak thinner. I have used Brodak sealer with fins attached with no issues.

 

[SCIGS30]

The problem I have with Estes instructions is that one or two primer coats will produce pretty bad results compared with the old instructions recommending balsa sealer. When I tried primer only, it took multiple coats with a lot of elbow work and a big mess. As you probably noticed Brodak sands with little effort. I did not enjoy FNF either, messy and finicky to get good results.

 

[SCIGS30]

TangoJuliet, My latest rocket would be tough to build, seal and sand with lots of tight areas. I am sure it can be done but that would slow my building up. Here are the brushes I use from Testors, keep them clean and they will last a long time. Also use a 50 percent off coupon at Michaels and they are cheap.
Chris, I still use FNF but man it challenges me, go figure....... I get the stuff on no problem, sand till translucent and it never fails, I sand too much and have to reapply to the areas I sanded down to the balsa. I end up taking more time and sanding more times with FNF than I do with dope based sealers. I don't plan on giving up FNF because I like the fact that I can use it inside. I am going out of town for a couple of weeks and would like to build a rocket during my down time, and there is no way I can use Balsa Sealer indoors so I will be using FNF. Damn it, someday I will master FNF.:smile:
https://www3.towerhobbies.com/cgi-b...q9DlrWK8zDEms05ie4z1R5WUJQDlZ3v3UIaAiD-8P8HAQ

 

[TangoJuliet]

That's a good looking model SCIGS30. I guess I need to get the Brodak Thinner. I've got brushes like that already. I was just using the epoxy brushes and throwing them out afterward. They're cheap brushes, but it does add up after a while.

 

[Woody's Workshop]

I don't like sealer. I sand, wood putty, paper, couple coats of TB and sand smooth with 220, prime, wet sand w/400. Looks like plastic and tough as nails.

 

[Sooner Boomer]

For a long time, I made my own sanding sealer by mixing baby powder into clear dope. You can tailor the mix; more powder, more filling and easier sanding - less powder, harder surface. I gave up sealing with dope because of the smell (I do a lot of work inside the house in the winter). I started mixing up water-based clear polyurethane instead. The added benefit is water clean up.

 

[lcorinth]

I started with CWF, but it frustrates me sometimes. So, I used some AeroGloss sealer, which, once I got the hang of it, I really liked. I haven't tried the Brodak yet. I want to, but the shipping is kind of high, so I need to buy a large amount of it to make it worth it, I think. I haven't found it anywhere except on the Brodak website.

I'm not a huge fan of papering, unless I'm leaving the fins square, which I rarely do. I recently did a good job of it though, probably for the first time, on an Estes Photon Probe (which I left square). I used paper and wood glue. I've used Avery labels in the past, but I've had them peel after a while. I've also tried spray adhesive, with some good and some poor results. I meant to try glue stick, but I let my glue sticks get old and they dried out.

My preference is for sanding sealer at #1, CWF at #2, and papering at a distant third. With just primer, I had to use so much of it to get the results I want, it got pricey.

Even when doing the sanding sealer, I think I prefer to do it before gluing. I like the idea of getting the fins on the rocket early, so I feel like I'm getting somewhere, but I think it's easier to sand if the body tube is not in the way. When brushing it on, I'm just really careful not to get any on the root edge. I haven't had any problems with fins popping off due to poor adhesion so far.

I've considered trying hcmbanjo's method of priming first, as it looks like it's a lot easier to sand everything without it all glued together, though I've never tried it. I usually leave a bit more primer on my rockets, so I can see whether I've actually got the surface smooth, so I like having a coat of primer on the whole thing to see what I'm doing. When I sand down to the paper, I sometimes overdo it and raise paper fibers, but I don't see that unless I put another coat on. But on this recent Photon Probe build, I really wish I'd tried priming first, then gluing. All the little fin bits make sanding a real chore on that one.

 

[Incongruent]

Do you saturate the fin in CA after papering? Doing so allows sanding without the fuzzies and increases the strength of the fin. I've used white glue and wood glue successfully, but prefer the white glue.
Papering works well with one beveled fins (such as on the Mercury Redstone) and air-foiled fins (crease the paper before gluing it on and it'll sharpen the edge) as well as square edged ones. With both sides rounded or two bevels there is overlap and/or a gap, but it can be filled and/or sanded down. Alternatively you can paper the surfaces and use CA, filler, or sealer on the edges (CA has the benefit of sealing the paper down as well).


Can you share a link to the primer you use?

 

[SCIGS30]

I still have not given up on FNF, mastering that stuff will really speed up my building. I can treat my balsa parts at work, on trips and other places where I cannot use my lovely smelling sealer. Right now I am working on 2 rockets and using FNF instead of sealer because I am not at home. I will post pictures when I am done.

 

[hcmbanjo]

I still have not given up on FNF, mastering that stuff will really speed up my building. I can treat my balsa parts at work, on trips and other places where I cannot use my lovely smelling sealer. Right now I am working on 2 rockets and using FNF instead of sealer because I am not at home. I will post pictures when I am done.

Using the Elmer's Carpenter's Wood Filler is like anything else, it takes a few tries to get a feel for it.
I brush it on with the grain, then against the grain which forces it into the pores.
Brush on one side of the fins, by the time you get to the fourth fin the first should be dry enough to do the other side.
Chances are there could be some warping but by the time the other side is coated it counteracts the warp and the fin should be flat.
If not, the fin can be gently bent back flat.

Let the filler dry overnight, that goes for body tube seams too.
I sand my fins using a Great Planes Easy Sander with their 220 grit on it.
Take down the bulk of the CWF coat with the 220 then switch to 400 grit to smooth it out.

Ideally you want to leave a very thin skin of the beige CWF on the fin.
One good coat of Duplicolor Primer/Filler and sanding fills any remaining grain.

The CWF does not seal the fins so glues will still soak in.
As shown in a above post I always sand off the primer where glue will be applied.

Doing it this way (and of course my way is the ONLY way, Hah!)
is a two pass fill. One CWF and sanding then Spray filler/primer and sanding - DONE!

 

[SCIGS30]

Chris, It sure sounds good, but I find myself sanding, looking good, then oops, down to the balsa. I sent you a pvt message, but my priming will not come until the rocket is put together, will not be able to prime the parts separately like you do.

 

[SCIGS30]

I was looking at your blog and the Gyroc was not primed until after the rocket was put together, and she came out nice.

 

[TangoJuliet]

Last weekend at work I assembled a Custom Rockets Equinox and an Estes Sky Warrior. The last two day at home I've been applying the Brodak to the fins on each, and the NC on the Sky Warrior, sanding in between coats... 3 coats.

So far I've concluded that I wasn't sanding quite enough before. I've tried the CWF (or FNF) a few times, and I think on those I sanded too much of it away, then with Aeroglass and now Brodak, I wasn't sanding enough. I'll still spray my filler primer and sand again before paint. I have no idea when paint will come though, we've been getting nailed with rain for almost a month! Today and tomorrow aren't going to be too bad, but it's still very humid - typical for this time of year on the Gulf Coast though.

 

[SCIGS30]

With the Brodak and Aerogloss sealer, I only use 320-400 grit sand paper, and sand just enough for a smooth surface between coats. I have to hold the fin up to the light to make sure I am sanding enough. FNF looks great until I hold it up to the light, then I see some bare spots or other imperfections and have to spot apply more FNF. I will do one fin with FNF and it comes out perfect, then the next 2 fins not so. I am still trying and will keep at it, It has been nice using FNF inside whenever I want prep fins. I just finished by Vintage Excalibur rocket and the fins look great with Brodak, I am shooting for the same results with FNF. I just built 2 rockets on my vacation with FNF and will post the pictures of how they turned out.

 

[TangoJuliet]

Dude! That looks perfect! :clap:

I just sprayed primer on the Equinox and the Sky Warrior. Sure enough, there were what appeared to be veins of unfilled balsa grain. I sprayed a couple of heavy coats. It'll have to sit at least 24 hours before I can sand it, otherwise it gums up the sandpaper too much. We'll see how it turns out after sanding.

 

[SCIGS30]

I hate when that happens, but luckily it has not happened in awhile. I just finished two rockets in 3 days and I tried my hand at FNF since I could not use Balsa Sealer where I am. I'm not completely happy with it but that is user fault not the product. I brushed on a heavy coat, sanded it down to a thin layer then had to spot touch some areas where I sanded too much. The kits are Estes Puma and Apogee Avion.