Papering Fins and Bubbling

[mh9162013]

Here's how I paper my balsa fins (for LPR and MPR builds):

1. Apply Elmer's white glue (school glue) or Titebond II to one side of the fin.
2. Use a custom-made scraper to coat the entire surface of the fin and remove as much glue as possible.
3. Apply the paper (basic, 20lb copy paper).
4. Set between two sheets of wax paper and that on top of one textbook and under about 3-6 textbooks (about 25 lbs-ish)
5. Let dry for several hours (or overnight).
6. Use a knife to cut away the paper around the fins.
7. Repeat steps 1-6 on the other side of the fin.
8. Coat the edges (but not root edge) with thin CA
9. Sand edges

The above steps have worked pretty well the past few years, but during a few of my last builds (BT-60 sized rockets with larger fins - Patriot, Red Nova and Green Eggs), I've noticed some bubbling of the papered fins. These bubbles are roughly oval in shape and are parallel to the balsa grains. These bubbles also only showed up when the rockets were stored (not yet painted or primed) upstairs in a low-humidity and warm environment (think 20-30% RH and 75-85 degrees F).

Initially, I figured that my bubbling was due to not using enough glue (or using a different type of glue), but that can't be it, as I didn't do anything different for these past few kits from the earliers kits. After some discussion and thinking, I believe my bubbling is due to one or more of the following variables.

1. Larger fin size. Instead of spreading glue around an Estes Wizard fin, I'm spreading it around the fin of an Estes Green Eggs rocket. The larger fin size means more time is spent spreading glue around. This means more time for the glue to dry and soak into the balsa before the paper is placed on top. With less glue bonding to the paper, bubbling is more likely.

2. Inconsistency in the balsa. The glue is soaking and bonding into the balsa at different rates due to the heterogeneity of the balsa wood's grains. This means the balsa fin surface doesn't bond to the paper in a consistent fashion.

3. "High" storage temperature. Keeping these fins in an environment that's warmer than where they were papered (storage = about 75-85 degrees and papering took place in about 65-70 degrees) meant any trapped air and/or water in the balsa had a greater chance to expand or evaporate more quickly and increased the risk of bubbling. I'm confident this is an important factor because one set of fins bubbled while being stored in the dryer and warmer environment for a few weeks. However, before going into this environemnt, it was stored in a cooler (55-65 F and 30-50% RH) environment for 3+ months with no bubbling.

I wanted to share these thoughts because based on my research here, people get seemingly different results when papering fins and bubbling despite using largely the same methods. Yes, the type of glue and amount of glue added to the fins are important variables (and the obvious ones). But I think there are other variables at play, such as temperature differential, speed in which glue is added to the balsa and balsa wood inconsistencies.

My take away (so far): I need to add more glue to larger balsa fins to make up for greater air drying and possibly more time for the glue to seep into the balsa. But I can't add too much, then I risk warpage and paper wrinkling. So how do I address this uncertainty? Build more rockets!

 

[neil_w]

This sort of thing is a good candidate for some semi-controlled experimentation, if you can spare the balsa. Otherwise just (as you say) build more rockets and track your process.

This sort of thing also makes me even happier about my own practice of papering with label paper.

 

[mh9162013]

This sort of thing is a good candidate for some semi-controlled experimentation, if you can spare the balsa. Otherwise just (as you say) build more rockets and track your process.

This sort of thing also makes me even happier about my own practice of papering with label paper.

I'd love to conduct an experiemnt, but I'm getting behind on client builds. So for now, I'll just take notes (mental or written) with my builds to figure out how to reduce bubbling. If I get the time to do an experiment, I'll update you all, I'm sure.

As for label paper, I've also completed a rocket build using that. So far, so good and it saves so. much. bloody. time! But it's less satisfying to do. And I know bubbling is still a possibility with label paper, based on my research here, so I'm not fully converted to label paper just yet.

 

[neil_w]

As for label paper, I've also completed a rocket build using that. So far, so good and it saves so. much. bloody. time! But it's less satisfying to do.

Yes, it is a big timesaver, and no warping and no piling weights on top of the fins to dry.

And I know bubbling is still a possibility with label paper, based on my research here, so I'm not fully converted to label paper just yet.

I have never had a single bubble, and I have papered a lot of fins.

What I believe to be a key step is to thoroughly remove the dust from the fin before applying the paper. For me, this consists of (a) brushing off the surface with a soft paintbrush, and then (b) using a piece of blue tape to lift off what remains. I don't think dust is a problem with glued paper, but it is definitely the enemy of label adhesive.

 

[Daddyisabar]

Brush off the balsa with old paint brush. Compressed air in the can! Sooooo fancy. Oopsie I'm out, well that means I will have to blow real hard! Feeling lazy, just wipe balsa on old jeans.

Never had any trouble with 3M lable paper fer bubbles. Got one once on a large balsa fin on TLP Matra Magic. Good thing I quickly noticed. Covered it up, ran back to the tailgate, made a quick Xacto incision, wicked in a little thin CA, a little spittle to speed up cure and back to the flight line. No one noticed so I can continue to shill for sticky lable paper.

 

[lakeroadster]

Clamping ensures no bubbling. Works for balsa and basswood.

​

 

[mh9162013]

made a quick Xacto incision, wicked in a little thin CA

That's the first step I used to fix the bubbling. But after priming and sanding, it is u-g-l-y. So a few days' worth of CWF + sanding + priming + repeat is needed. Ugh.

 

[Daddyisabar]

That's the first step I used to fix the bubbling. But after priming and sanding, it is u-g-l-y. So a few days' worth of CWF + sanding + priming + repeat is needed. Ugh.

Don't sand too hard. Just prime the paper and a very lightly sand with super fine for a glass like finish. Love the paper, caress the paper. It will love you back!

 

[mh9162013]

Don't sand too hard. Just prime the paper and a very lightly sand with super fine for a glass like finish. Love the paper, caress the paper. It will love you back!

There are so many gashes and bumps, light sanding will never produce a smooth finish, unfortunately...

 

[Back_at_it]

I was never a fan of papering fins. I tried copy paper, notebook paper etc. etc. then finally tried card stock and it worked sort of alright. Fewer bubbles, and for the most part, no ripples in the paper.

At one point I was building something with epoxy and had some left over and thought to myself, I wonder how this would work with papering fins. As they say, the rest was history.

No bubbles, no ripples, no tears, and more than enough time to get everything coated on both sides and left to cure. Additional benefits is that the epoxy soaks in and strengthens the base materials and nothing warps so you don't need to worry about weighing them down. I still do it but it's unnecessary.

 

[Daddyisabar]

There are so many gashes and bumps, light sanding will never produce a smooth finish, unfortunately...

Oopsie. Maybe time to start over and do it the Jedi way. Patience, keep your mind on where you are at, what you are doing. There is no trying, just doing. Feel the force flow through the tacky glue, the cardstock, the squishy balsa. No instant gratification, hard work and preserverence will lead you to your destiny.

NO THANKS, I THINK I WILL STICK TO SITHY LABEL PAPER.

 

[K'Tesh]

My experience with bubbles under the paper is that they occur when the fins are primed and still wet with paint. Upon drying, I can't find the bubbles anymore.

https://www.rocketryforum.com/threads/papering-balsa-ply-fins-a-foolproof-method.65628/

 

[mcderek]

This is what I use to paper fins. In fact, I'm about to paper a Frick-n-Frack. maybe I'll do a build thread?

 

[bjphoenix]

Here's how I paper my balsa fins (for LPR and MPR builds):

I don't do it all that much differently, I can't see anything you are doing that I think would cause bubbles, I've never had any significant bubbles.
I use Titebond II, I clamp the fins between 2 plastic sheets and 2 pieces of smooth plywood. I put glue and paper on one side of a fin and clamp it, wait 30 minutes then do the other side of the fin and leave it clamped about 12 hours.
I put the glue on, spread it around, then wipe off most of it with my finger. I don't leave very much glue on there, maybe you are taking off more than I do.

 

[mh9162013]

I've been doing more thinking, and I think the bubbling is triggered by the warmer temps, but the underlying cause is that not enough glue is sticking between the paper and the balsa. I've been trying to think of ways to address this.

One possibility is coating one side of the balsa with a thin later of glue, just like I do already when papering the fins. But instead of adding that paper, I let it dry. Then when I'm ready to do actual papering, I add another layer of glue (as thin as possible, just like the first time) and add the paper.

I'm worried about the warping potential, though. Maybe I can make some tool to hold the fin flat and use a small air heater (or hair dryer) to quickly dry the glue; shouldn't take more than 60 seconds. But even if that works, that's a lot of extra work when simply keeping a little bit more glue on the fin might suffice.

I also think my bubbling issue is also caused by bigger fins (more time for the glue to dry and more balsa material to suck up the glue before it can attach to the paper).

Also, just to reiterate: the bubbling occurs days or weeks after the papering is completed and only when the partially completed rockets are stored at temperatures that are easily 10-15 degrees warmer than when the fins were originally papered.

 

[mh9162013]

One possibility is coating one side of the balsa with a thin later of glue, just like I do already when papering the fins. But instead of adding that paper, I let it dry. Then when I'm ready to do actual papering, I add another layer of glue (as thin as possible, just like the first time) and add the paper.

Update: I recently did this with an Estes Nike-X fin (the largest one of the 3 types) and it was really easy to coat the balsa and dry it flat (I used two straws laid on the fin with a sanding block on top to keep things flat).

Over the next few days or weeks, I will do some testing by comparing this method of papering with my original method (as mentioned in the original post). I think my testing method will involve holding the fin within a very warm air stream (like in front of a small space heater...I'd guess the fin would be exposed to air that's around 90-110 degrees F) for 12 or so hours. Will report back with my findings.

 

[aerostadt]

I used 20 pound stationery and white glue applying the paper to the balsa for the large wings on my Double Shuttle. I applied the glue to the paper first smeared on with my fingers and then pressed the paper onto the balsa. I may have used aluminum foil at first to press the paper to the balsa with heavy books on top. I had to do both sides, because warping could be a problem. Eventually, I used parchment paper onto top of the glued paper with books on top. Parchment paper was much better. With this method I got wrinkles in the fine product, but it was tolerable. The last Double Shuttle I did something different. I put adhesive paper on the balsa and then applied white glue with a foam brush and finally parchment paper and books on top. The warping almost disappeared along with wrinkles disappearing. Building time was faster with the second method and I could cut the finished material with a scroll saw.

 

[Hobie1dog]

After reading multiple threads on papering fins i've decided I'll never do it

 

[cwbullet]

After reading multiple threads on papering fins i've decided I'll never do it

It works well if you do it right.

 

[bjphoenix]

I used 20 pound stationery and white glue applying the paper to the balsa for the large wings on my Double Shuttle. I applied the glue to the paper first smeared on with my fingers and then pressed the paper onto the balsa. I may have used aluminum foil at first to press the paper to the balsa with heavy books on top. I had to do both sides, because warping could be a problem. Eventually, I used parchment paper onto top of the glued paper with books on top. Parchment paper was much better. With this method I got wrinkles in the fine product, but it was tolerable. The last Double Shuttle I did something different. I put adhesive paper on the balsa and then applied white glue with a foam brush and finally parchment paper and books on top. The warping almost disappeared along with wrinkles disappearing. Building time was faster with the second method and I could cut the finished material with a scroll saw.

I've had some wrinkling- the paper soaks up the moisture in the glue and swells. I changed my procedure to use less glue and to get the paper on and the fin clamped as quickly as possible. I do one side at a time to get them clamped quicker. To control warping I do one side, leave it clamped about 15 minutes then do the other side and leave it all clamped overnight.

After reading multiple threads on papering fins i've decided I'll never do it

I don't build anything that isn't papered. It makes the fins smoother and more importantly to me it makes them stronger. It does take longer- cut out the paper, glue the paper on, sand the edges, touch up any booboos. I plan ahead and don't get in a hurry.

 

[aerostadt]

Another thing I did was iron the papered fins. The white glue contains vinyl, which can be ironed. I used an iron that I used for monokote.

 

[mh9162013]

Another thing I did was iron the papered fins. The white glue contains vinyl, which can be ironed. I used an iron that I used for monokote.

That's a neat trick to have handy. I've only had my papered fins warp once, and that was only when I did one side. After papering the other side, it was fine.

But if I do finish a fin and it's warped, it's good to have the iron as an option.

 

[allensmith]

After reading multiple threads on papering fins i've decided I'll never do it

I was hoping to add this technique to my skill set, but it looks like it really is a “skill” that has to be worked at. Glad I have a lot of simple builds with the grandson. Maybe we can hone the skill for the bigger projects he has lined up for me.

 

[neil_w]

Papering with Avery labels suffers none of these problems. It is so much easier. If nothing else, it might be a much easier technique to start with.

There are definitely circumstances when the *additional* strength (label paper *does* add considerable strength on its own, but not as much) of glued paper is necessary or desirable; I did it myself in one particular instance. But for the vast majority of the time, it's labels for me.

I've been wanting to create a video show exactly what I do, but don't have a suitable camera setup. Maybe I'll do a tutorial with photos, although a video would be much more useful in this instance. Will ponder.

 

[mh9162013]

I was hoping to add this technique to my skill set, but it looks like it really is a “skill” that has to be worked at. Glad I have a lot of simple builds with the grandson. Maybe we can hone the skill for the bigger projects he has lined up for me.

Our discussions sound intimidating, but it's not has hard as it seems. Yes, you get better with practice, but if you follow some basic guidelines, you can get good results.

I think my issue is primarily the result of papering the fins at one temperature, then storing the rocket at a different one. No, papered fins shouldn't bubble with only a 15-25 degree temperature change, but I think many people who paper use more glue than me because they use their finger to remove the glue from the fins when I use a special squeegee tool that does a very effective job of removing the glue from the balsa fin's surface. I'll post a picture of squeegee tool in a few minutes.

 

[mh9162013]

Papering with Avery labels suffers none of these problems. It is so much easier. If nothing else, it might be a much easier technique to start with.

There are definitely circumstances when the *additional* strength (label paper *does* add considerable strength on its own, but not as much) of glued paper is necessary or desirable; I did it myself in one particular instance. But for the vast majority of the time, it's labels for me.

I've been wanting to create a video show exactly what I do, but don't have a suitable camera setup. Maybe I'll do a tutorial with photos, although a video would be much more useful in this instance. Will ponder.

From what I've read, it can still bubble, but I'm guessing there are ways around that to reduce or eliminate the risk.

Even if the bubble-risk of Avery-papered fins is equal to regular glue-and-paper papering, it's still a worthy alternative because of the immense time savings (although it may cost a small bit more money).

 

[SolarYellow]

Maybe if you squeegee glue on both the paper and the balsa, you'll get enough penetrating into both surfaces to meet in the middle and form a more consistent bond.

 

[mh9162013]

My squeegee tool:

 

[mh9162013]

Maybe if you squeegee glue on both the paper and the balsa, you'll get enough penetrating into both surfaces to meet in the middle and form a more consistent bond.

There's not enough time. Plus, if you add glue to the paper, the paper is more likely to wrinkle (wrinkles in the paper are easier to fix that bubbling, though).

 

[SolarYellow]

I've just used an old hotel room access card as a squeegee. Works great for me.