seal and sand AFTER building??

[wwattles]

On several of the kits I've built recently (Squirrel Works and Fliskits), they've said in their instructions to seal and sand the balsa parts. Good idea, since it makes the balsa finish better, paint smoother, and overall improves the performance and appearance of the kit.

But why do they leave that instruction until the very end, at the "finishing" stage? I, for one, have a hard time doing accurate sanding in tight corners, such as those created at body/fin joints or wing/tail joints (such as on the Red Baron boost glider). Why not seal/sand BEFORE construction, when it's a lot easier to get a good surface?

WW

 

[OKTurbo]

Everybody has their own "tricks" to finishing. I usually do exactly what you're suggesting. If possible, I try to fill and sand the fins BEFORE I glue them on. It makes it much easier to sand them when they're not attached. About the only thing to be careful with when doing this is that it is easier for the fins to warp when they are not glued on. Other than that, for me, that is the easiest way to get a good finish.

On something like the Red Baron, you need to be sure that you get a good wood/wood joint for the glue to hold. So you'll need to either keep the filler off the joints or sand it down to bare wood when you put it together.

John

 

[Micromeister]

I sometimes rough fill and sand balsa fins before application. But I rarely finish until after the model is complete. Its much better to fill file sand and finish, fillets, fins, transitions and nose cones at the same time your finishing the body. It's much easier to get those seamless, flawless finishes AFTER all the major parts are attached. tiny scale detail may be applied later but it's really tough to get a good clean invisible joint after finishing.
I also like filling and sanding before painting so I can apply a lot of pressure to the fin/body joint to ensure strong stable joints, if a fin/body joint or fillet fail while sanding It can be fixed, If it fails in flight the whole model is usually junk.

 

[powderburner]

One consideration in setting the sequence: if you cover your balsa fins with sealer and primer before assembly, you will probably get less penetration of adhesive when assembling the fins to the BT.

How much less, I can't say. Whether it makes a structural difference, I can't say. But I would vote for assemble first, seal later.

Someone here on TRF once posted that he masked about 1/8 inch of the fin near the root while sealing and priming. He did this on purpose to leave part of the balse nekkid, giving the glue/epoxy/whatever a chance to get a good grip. That is probably the best hybrid approach?

 

[SecretSquirrel]

Originally posted by powderburner
One consideration in setting the sequence: if you cover your balsa fins with sealer and primer before assembly, you will probably get less penetration of adhesive when assembling the fins to the BT.

Exactly!

How much less, I can't say. Whether it makes a structural difference, I can't say. But I would vote for assemble first, seal later.

Quite a bit less penetration sometimes, and it does make a structural difference.

 

[Fore Check]

The other thing to conider is any warping action you may get on your balsa fins when the sealer/filler is applied (it *will* happen.)

Anyway, gluing your fins to the BT reduces the warping action when the sealer/filler is initially applied.

I *was* in the camp of sealing the fins prior to application until I found the aerosol sanding sealer that I now use. Since then, I've had significanty better results.

I now fully subscribe to the "seal last" theorem.

 

[DynaSoar]

Originally posted by Fore Check

I now fully subscribe to the "seal last" theorem.

Same here. A good spray sealer will also help fill tube spirals and smooth over small bumps on fillets. I swear by Deft spray lacquer sanding sealer for this (and use the brush-on when I can't find the spray). Besides, sanding the fins after attachment can include sanding the fillets if they need it.

 

[Silverleaf]

I used to seal the fins as well, and mask the edge, then glue - but after having problems with a Quest Tomahawk, I changed.

I sand the fins first, down to fine sandpaper, then attach, and finish all construction. Then I use a sanding sealer 3 X's, then sand smooth down using medium fine, next 2 to 3 coats of primer, sand smooth again, finish coat in 3 layers, add decals, then seal with gloss, then flat.

I've yet to use Future on any models, - keep forgetting to pick up a bottle when I'm in town - but so far the finish on the Orion 2 and Gordon's Little Joe 2 look great

 

[Stewart32]

inasmuch as possible. Especially when it comes to the fins. Although, this has caused a problem with adhesion at least one time on some surface mounted fins..

I have tried several sealing/strength techniques on balsa fins including:

paper laminate
tissue laminate
elmers sanding sealer
bondo
elmers glue
and CA

CA seems to do the trick for me. Two thin coats with sanding between applications while the fins are still in sheet form.

 

[fehskens]

>Someone here on TRF once posted that he masked about 1/8 inch of the fin near the root while sealing and priming. He did this on purpose to leave part of the balse nekkid, giving the glue/epoxy/whatever a chance to get a good grip. That is probably the best hybrid approach?

I generally seal after assembly, but if I expect that to be difficult I will mask (with masking tape) the areas that shouldn't be sealed (e.g., fin root and a small adjacent strip for a glue fillet) before sealing.

len.