How to seal balsa

[Neptune]

Yes, you read it right, I don't mean "steal"

So I have to make closed lifeboats for the Chaconia, yet I'm not entirely sure on how to go about that. My plan was to carve and shape them from Balsa, but that has a rather grainy appearance, so I'd need something to cover it to smoothen it out. Any idea what can be used for that?
I suppose a very thin layer of milliput will just break off when sanding.

Does somebody have experience with different methods of building such lifeboats? I made a start a couple of years ago, but with styrene, with the intent to fill up with styrene pieces and finally shape it with milliput, much in the same way as I build hulls in 1/700 or 1/400. It just looks rather difficult to make a complete and complex item like a closed lifeboat like that...

[biggles2]

Many, many, many coats of varnish.

[a380]

thin ca. soak, dry, sand, varnish
example:
http://www.bsi-inc.com/Pages/hobby/ca.html

[doog_k]

Cellulose Dope, thin coats first, sanding between. I coat larger areas (1/144th scale hulls) with model aircraft tissue too, again layers and sanding between.

[wefalck]

Why bothering with Balsa wood ? You don't say anything about the physical size of the boats, but I would rather carve them from some denser wood. Some pine will do and is easily available everywhere. For really small ones it would be better to use fruit tree wood (pear, cherry) or boxwood/capelo wood. All these woods give a nice finish after a coat of sanding sealer.

wefalck

[pghgeorge]

Maybe thinned out epoxy resin, or 20 minute epoxy. Thinned with rubbing alcohol.

[Neptune]

Thanks for all the tips. I'll have a look at how I'll do it. Got some spare balsa as well, so I can experiment. Eventually I guess I can still fill up gaps between frames with balsa pieces and then give it a 2mm layer of milliput as a finishing surface to sand. I'll have a look. The problem with milliput in this case would be that you have to push it rather hard to flatten it out.
I had a similar attempt with insulation foam between the frames. The problem I encountered was that the frames moved back and forth during sanding, creating cracks between the milliput and the frames. Balsa is harder than insulation foam, but still, the risk is there.

[Admhawk]

Dope is the traditional way, but it starts to get pretty thick and unless you spend a lot of time on it, will still look pretty bad.

Cyano (crazy glue) is much better and harder. It can be a bit messy putting it on, but just use your finger to smooth it. It will peel off your finger after a couple of days. Sand and coat again, then sand. Repeat until it's smooth enough for you. It's hard and durable, won't flake off, easy to paint. Several friends use it for professional model building. I've used it for making masters out of bass wood.

For flat or gently curved surfaces, use it to glue thin styrene to the outside, instant smooth surface.

[wefalck]

One can also use the Balsa-hull as a plug for 'vacuum'-forming. Fix a thin sheet of styrene in a cardboard frame, heat it gently with a hairdryer until it starts sagging and then pull it over the (pre-heated) plug. If you have only one boat to do, you can leave the plug in for stability. Otherwise, you can fill the shell with expanding foam.

Still, I am wondering, why one would go and built such a tiny thing as a 1/100 scale lifeboat using the bulk-head method. I would use the negative bulkheads as templates and carve the hull from solid wood.

wefalck

[tweety777]

Interesting question, I sort of having the same problem.
My lifeboats for Well Enhancer are to be made of fibreglass as they need to have room electrical equipment and propulsion and need to be light enough to float.
I decided to use balsa for molds as that appeared to be smooth enough after some sanding with fine sanding paper.
Now that I've found this topic I'll be more careful and will fill the entire molds to make sure the finish is very smooth.

Greetings Josse

[Neptune]

Some good ideas there Wefalck. Indeed, they will be 1/100, total length I think was around 8cm. I only need two of them, so making a real mold isn't an option. Carving it from harder wood is also an option, yet I'll have to combine with styrene to reach certain detailing and shapes. Using styrene to cover it has also crossed my mind. My starting attempt was actually like that. Bulkheads, with flat surfaces from styrene, and then the intention to make the curves (rather complex) with milliput.

[rd2jones]

I have had good luck making 1/200 ships boats (25-foot gigs, so about 3.5 cm long) from polymer clay. I use an armature to support the clay while I shape it.

The armature is in two pieces: a plan view of the boat cut from used offset press plate (thin aluminum sheet) and a profile view ditto. Glue the profile piece down the center of the plan piece (CA glue) so you have a shaping guide to hold the clay and get the curves right. In cross section, the armature will be a T shape with the plan piece as the crossbar and the profile piece as the upright. (I hope that makes sense)

Then shape the clay into the armature to form the hull. You have to do a good job here, since the clay is quite hard after it's baked-- so the better the original shaping, the less final filing and sanding you'll need to do after it's baked. When you have the hull shaped to your liking, put the whole thing into the oven and bake it as per the clay instructions. It will likely need some touch-up with file and sandpaper after it has cooled.

Don't use styrene for the armature since it will shrink when baked, and balsa is too flimsy. The aluminum offset sheet cuts easily with good scissors.

In my case, I used the completed clay hull as a plug for slush-casting the boats in resin, as hollow hulls. You only have two boats and they are closed in, so just making up two hulls as I've described may do the trick.