Is this the right way to treat balsa parts? Two coats of wood filler,two coats of sanding sealer, two coats of primer, two coats paint and two coats of clear gloss . I sand between all coats and let each coat cure for 24 hrs. So as you see it takes me over a week to do even a level 1 rocket Is my method overkill and do all steps need a 24 cure time? thanks
Yeah, I'd say it's overkill... here's what I do, and it works perfectly for me...
First, you need to fill the grain on the balsa. You can do this in several ways. For nosecones, due to their round, complex shape, usually the thing that I do is apply ultra-thin CA (pink bottle stuff from Hobby Lobby, otherwise "water thin" CA will do) outdoors to the cones from the shoulder to the tip, letting the cone "drink in" as much CA as it wants. This hardens the balsa somewhat and seals off the pores. Don't get it on the shoulder of the cone or transition that goes down into the tube if you can help it, and of course don't glue the cone to your fingers, or anything else. Set it down on wax paper to dry. It can get hot from the CA reaction, and the fumes are NASTY, so do this outside. It'll dry in about 30 minutes or so and be ready to sand smooth with 220 grit sandpaper. Don't worry about getting it perfectly smooth, just sand all the "grit" and roughness off it from the CA treatment.
For fins, I prefer PAPERING them. Cut your fins from the balsa sheet, stack sand them to identical size/shape, and then sand in whatever airfoil you desire, usually at a minimum a rounded leading edge (which cuts drag about 50% alone). Take ordinary printer paper and WHITE glue, and apply a VERY VERY THIN layer of white glue to the paper where the fin will go, and press the fin down onto the paper with the leading edge toward the center of the paper. Spread another VERY VERY THIN layer of white glue onto the top surface of the fin and then fold the fin and paper over the leading edge of the fin, keeping everything taut, and press the fin down firmly. Use a round ended round barrelled tool (like a Sharpie marker) to 'burnish" the paper down tight to the fin surface and squeeze ALL the excess glue out from between the paper and balsa underneath. You HAVE to use a VERY thin layer of glue-- use too much glue and the paper will turn to mush and wrinkle or tear. Work from the front leading edge center of the fin toward the back and outside edges of the fin, and "outline" the fin with the end of the Sharpie marker to crease the paper over the fin edges. FLip the fin and repeat. Allow to dry overnight. Cut the fin from the paper with a SHARP (new) hobby knife blade, shaving the paper down to the edge of the balsa on the root, tip, and trailing edge. Draw the fin across a sheet of 220 grit sandpaper a couple times on each of these edges to "shave" any paper 'hairs' off the edge of the paper, and the fins will be ready to glue on the rocket-- no further filling/sealing or sanding required! Plus, you've just about DOUBLED (or more) the strength of the balsa for VERY LITTLE weight gain. Win/win/win in my book!
If you don't want to paper the fins for whatever reason, you can either elect to treat them with CA like the nosecone/transitions, or just move on to filler...
The nosecone and transition, even when CA treated, will still have a lot of grain showing... The CA wicks down deep into the fibers of the cone, transition, or fin, and help seal off the wood grain and glue the fibers together to add a little strength, but the grain will still show. Papering cones isn't particularly feasible so filler is still needed. I use regular Elmer's Carpenter's Wood Filler. Take a dollop and put it in an old baby food jar, or other small sealable container. Add a few drops of water, working it in with a paint brush, to mix the filler and water until it's the consistency of regular hot dog mustard... thin, but not TOO thin. Now you can brush it onto the parts with a 1 inch paintbrush. Once you've brushed on a nice, even coat, (don't worry too much if there are brushstrokes showing, so long as everything is covered pretty uniformly) and set it aside to dry, usually overnight, or at least a few hours. Once dry, the stuff sands off quite easily with 220 grit sandpaper... sand the fin/cone/transition until most of it is gone and you can see through the filler to the wood underneath. If necessary, switch to 400 grit sandpaper for a short second sanding to smooth everything out slick as you please. Sand in SMALL CIRCULAR MOTIONS-- DO NOT sand in straight lines, or you'll get sanding scratches. DO NOT push the paper down hard into the surface; this just creates heat and plugs the paper and wastes time and energy and ruins the sandpaper, and puts deep sanding scraches in the surface. Sand lightly and let the paper do the work. Turn the part continuously in your hand as you sand, DO NOT sand in one spot, or you'll get flat spots and an uneven surface. Wipe the part frequently to remove dust, and inspect the surface by holding it up to the light.
Once you've got the parts sanded down smooth from filling, you're ready for primer. I use the double-glue joint method to join fins to the rocket, so I apply a thin layer of yellow wood glue to the root edge and allow it to dry-- this will allow the glue to penetrate the fin and make a stronger joint. If you're going to CA treat the fins rather than paper them, you should do this step first, so the CA doesn't seal off the fin root wood grain before you apply the yellow wood glue... the CA would prevent it from soaking into the wood grain since it'd already be sealed off by CA, making a weaker fin joint. Double glue joints are stronger than either the tube or the fin, and nearly as fast as using CA to attach the fins, but without the brittleness and low shear strength of CA. Depending on the rocket, I usually glue the fins on first, then primer and paint. If the rocket uses extremely complex paint patterns, sometimes it's better to primer and paint the fins first before gluing them on... just depends; you'll have to decide.
Spray a good coat of a high quality sandable primer on the rocket. Put a light coat on first, then a little heavier with each subsequent coat, about 20-30 minutes apart (read and follow the primer directions). I usually put about 2-3 coats of primer on the rocket. Allow to dry overnight. Sand with 220 grit sandpaper, removing MOST of the primer, but DO NOT sand through it, if you can help it. If you do, a light touch-up and gentle resanding of those areas should do. Sand lightly in small circular motions, and keep the rocket moving. Sand the rocket again with 400 grit, to remove any sanding scratches and make the surface silky smooth. Wipe the rocket off, and hold it up to the light, at an angle, so you get a "glint" of light off the rocket parts... inspect this reflected 'glint' of light for any imperfections... scratches, warps, surface irregularities, pits, voids, or other imperfections in the surface will be readily apparent by this method in the reflection of light off the tube. Either sand these spots smooth with more 400 grit sandpaper, or spray a little more primer, allow to dry, and resand with 220 grit and 400 grit again, until it's smooth. I often will "damp sand" the rocket, nosecone, or parts with 400 grit wet/dry paper... cut the paper up into 2x3 inch squares or thereabouts, dip it in a bowl of water, shake off the excess, then gently sand the rocket as previously instructed. The moisture on the paper mixes with the sanding dust to make "sanding mud" which lubes the sandpaper and surface, prevents the paper from clogging, and makes the surface EXTREMELY smooth as you sand. Periodically dip the paper in water every few minutes and rub your thumb across the grit of the paper underwater, this will remove trapped paint particles and make the paper just like new. SAND LIGHTLY. Use a damp paper towel do wipe away the sanding "mud" and then a dry paper towel to wipe it dry. It DOES NOT take a huge amount of water... just the residual dampness on the paper or an occasional DROP of water will suffice for all this. When you're done, the rocket should be as slick as smooth as can be, and if you hold it up to the light, the glint of light will SHINE off the tube... any imperfections are easily visible, but 99.5% of them should be gone. This whole process takes maybe a couple hours at most...
Let the rocket dry overnight just to ensure no water remains in/on the primer... now you're ready to spray your color coats. Apply the lightest colors first, then the darkest. Light colors are usually pretty poor at covering, and it will take many coats to cover over previously applied dark coats, whereas dark coats usually cover light coats very easily. Apply the paint in several THIN coats, about 20-30 minutes apart, starting with a very light coat and getting a little heavier each time... start spraying before the can is pointed at the rocket, and keep spraying after you passed it. Keep the rocket moving and don't paint in the same spot again or you'll get runs, sags, or drips, which will have to be sanded out later. Don't get the can too close to the surface of the rocket, and don't move the can too slowly... better too fast than too slow... too slow and you'll get runs, drips, and sags. Once you've applied 2-3 coats or so and you're satisfied with the appearance, and the paint has flowed out on the surface smoothly and evenly, allow the paint to dry overnight. It should be smooth and slick with NO further sanding required!
Follow the paint instructions on topcoats. Most paints have DEFINITE 'recoat windows' or "topcoat recommendations" that should be followed to the letter, unless/until you have successful experience otherwise. I don't usually bother with any clearcoats or anything, because 95% of the time they're not necessary. 98% of a great paint job is SURFACE PREP WORK... many people make the mistake of thinking they can rush the prep work and the paint will cover the defects... this is ABSOLUTELY UNTRUE.... paint MAGNIFIES surface defects, it does NOT hide them! Put a good primer coat on the rocket, sand it out beautifully, and then CAREFULLY apply the color coats and the rocket will look terrific with no further work. Botch or rush the primer and sanding work, (or the filling and sanding work for that matter) and NOTHING you do will make the thing look great! The actual painting of the color coats is only about 2% of the work of getting a great paint finish, but it's a CRITICAL step... you cannot get a great finish with botched or rushed prep work, but you can RUIN beautiful prep work with a botched or rushed paint application! They must work together!
IF you REALLY want the paint to look a mile deep, have a deep glossy shine, or feel the need to "protect' the paint with a clearcoat, follow the can instructions to the letter regarding cure times-- DO NOT rush this step, as outgassing of the paint can continue for a considerable amount of time, and rushing now will likely ruin all your work. When the paint is fully cured, you can either wet sand the color coats with extremely fine grit sandpaper, polish the paint with polishing compounds to bring out a deep luster, or apply your clearcoats or topcoats. There is little point to sanding or polishing a paint surface you intend to clearcoat or apply a topcoat finish (like Future or various car polishes) to... in fact, it can be COUNTERPRODUCTIVE, by making the surface too smooth for the clearcoat to stick well to it. If you're going to clearcoat, DO NOT sand the color coats of paint-- apply the clearcoat, allow it to FULLY CURE, then wet sand or polish the clearcoat to a deep luster. If you're just applying Future or car polishes (Nu-Finish, etc) then you can wet-sand the color coats with extremely fine paper, then apply the finish product of your choice per the instructions. Like I said, for 99% of the stuff I've seen and done, it's not even necessary at all... the color coats should turn out SO pretty, IF you've done great prep work and applied the paint well, that no further surface work is required.
Good luck! OL JR