Filler and Dope

I can only tell you what not to do at this stage. I have been using the "Rocking Donkey" as a test bed until I got bored with filling and sanding but I came up with a few conclusions.

I made it light - it only weighed 40g - wood only.

I applied coat after coat of sanding sealer, sanding back after each coat, but in its own - it did not fill that well and high and low spots were difficult to see. After many hours - I had increased the weight to 45g but was causing more dings by my clumsy handling.

I then decided to use silver dope. Initially, I was pleased - spray on, dry and sand - high and low spots stood out. Deeper ones - I filled with acrylic putty - sanding most of it away. I ended up with a very smooth finish but .....................WEIGHT NOW 60g!!!!

I sanded back and back and back - got it down to 52g but with bare wood exposed. Resprayed with dope and back to 55g.

Gave up and painted it. Used acrylic paint for a matt finish and added another 5g. Still needs fuel proofing.

What did I learn? The silver dope I used had a weight penalty but it was an excellent way of picking out high and low spots. I created more work by little accidents (e.g. finger nail gouges, squidging balsa between thumb and forefinger while holding it ........)

I think I would have been better off applying tissue.

I have been experimenting with glass cloth (0.6g per sq. meter and a water based resin called EZE-KOTE on another model and that is looking promising.

http://www.deluxematerials.com/products_building.html

I thing aerokote may be for the final fuel proof finish. I thought about it but gloss wouldn't look right on "Rocking Donkey".

The old fashioned way was to mix talcum powder (cheapest bought from a supermarket with dope) but I remember it didn't spray very well and needed constant stirring when brushing. It did a good job as a filler but it is only recently that I have been weighing stuff before and after.

Thanks guys,

The model in question is solid balsa, no tissue. I was doing well keeping it blemish free until I started installing the control system.

I think the talc would be good to smooth the graining however, my gouges will need some more attention.

I was hoping plain old wood filler might work or perhaps spackle?

Ron

Ron, I would pass on the talc. It can really give you a false sense of smoothness not to mention adhesion problems. If your dead set on achieving a high shine finish with dope, your going to need silkspan over the wood. It takes very little time to do it and it seals the wood grain far superior then the dope ever will. It also prevents the paint from sinking back into the grain. It will do this even with silkspan but not to the degree if you chose not to use it. Sanding sealer provided from the specific dope manufacturer works, I personally don't use it. I can achieve a far better finish using high build primer and wet sanded off. Once you've provided a decent base, the finish just goes along for the ride. Spraying dope yields a far better finish. It also allows you to easily control the amounts your placing on the plane. It's essential to have enough clear over the color to allow for sanding the clear. This is very tedious. I generally start knocking down the clear with wet 600 followed by 800 and soapy water. I go to 1200 followed by 1500. When the entire finish is completely dulled down and looks matte like, I know I'm ready for rubbing.

Sanding on solid surfaces are one thing, sanding on open bays takes a lot of discipline to keep you motivated to finish. Take a old sock and place it on your hand like a puppet. Using your index and middle finger begin by using Brasso brass polish on the sock and start working it into circles with those fingers. The liquid Brasso will start to solidify and this is where you really start rubbing harder and harder generating heat. It's going to feel like your fingers are burning. Keep working 1"x1" squares like this 1 at a time. When your rubbing it's going to start squeaking . Buff off with clean soft towel and when complete follow with carnuba wax.

Imho, filler is usually a bit "heavy" handed.
If you go the spackle route Ron, the key word
is "lightweight".

....but you knew that.  
Bob

Thanks Ken,

I guess I had better pick up some Brasso. Silkspan is going to be a pain since the whole model is assembled. I'll give it a go though.

Bob, I didn't know.... Thank you.

I silkspanned the Yak fuselage and rudder with Polycrylic and though still in the hack job category, it came out as glassy as I needed with almost no extra work. Just Rustoleum primer over the silkspan and sanded and re-primed a couple of times and then on with the paint. Only one coat of flat paint and wet sanded that...carefully. I spackled any deep low spots and brush the dry sanded spackle with CA. The clearcoat created the glassy shine. I had read that flat adheres better and is lighter. And I found it did cover much better than the same amount of glossy paint. That's a lazy man's way. Ian, Ken and Windy would probably fire me.  
Lazy Rusty

Lol, I am confused now.

What do I tack the silkspan down with? I am using Aerogloss clear and then color. I have sanding sealer, but do I even need it with silkspan?

By silkspan, do you mean actual silkspan or just the tissue that comes in the kits?

Cribbs74 wrote:Lol, I am confused now.

What do I tack the silkspan down with? I am using Aerogloss clear and then color. I have sanding sealer, but do I even need it with silkspan?

By silkspan, do you mean actual silkspan or just the tissue that comes in the kits?

The kit tissue. It has a grain and I run the long grain lengthwise on the sanded bare balsa fuse. I didn't use sanding sealer. I applied onto Minwax Polycrylic, then lightly applied some more poly on top of the paper and then lightly squeegeed the excess off. I tried a test piece with Minwax Polyurethane and it did not look as good, not at all. The polycrylic left it looking like bare wood, sans grain. Then lightly sand it, spray primer and wet sand twice, then and paint your color and Lightly wet sand. Then clear.

Ron, coat the plane, fuse , wing or whatever your intending on painting with thinned dope 60% dope/40% thinner. After the second coat , scuff the airframe lightly with 240. Put on another coat 3rd coat but this time go 50%/50%, at this point, the wood is or should be starting to look glossy when dry.The One time spackle is really not compatible with dope. I've used it, but I would consider sealing it with thin CA over it if you choose to use it. If your covering a wing start with the bottom first, the sheets of silkspan (Typical of what came in old kits) should be cut to size but oversize at least 2". I lay the sheets down and spray with a mister water bottle and get them saturated. I then pick the sheet up and lay it on my chest stretching it out. Your shirt can take out the residual water leaving the sheets wet enough to stick but not overly wet. Place the silkspan on the wing panel and begin stretching it out. Once the majority of the wrinkles are gone, take your dope brush and begin brushing through the silkspan. At this stage I go back to the 60%/40% mix and brush quickly through the silkspan . BRUSH with the ribs and parallel to the other parts. If you choose to brush perpendicular to sheeted areas or leading and trailing edges puddles will form through the silkspan. This is like the paint brush is hitting a speed bump and dumping through the fabric. Brush off of the work and not into it. Using your fingers roll the silkspan around the leading and trailing edges firmly securing it. THis is especially important on wingtips and areas that the sillkspan terminates like wing sheeting to fuselage. Firmly run your finger over these areas and work out all air bubbles.

Once dried, the silkspan will obviously be tighter but wrinkles still may be present. Also, solid areas( Leading , and trailing edges should be knocked down with fine sandpaper). Don't sand through the silkspan, just sand enough to scuff and take off any hitchikers on the surface. At this stage, 2 more coats and go to color. I like to spray a couple of protector coats of clear after the color and this is generally all that's needed for a sport finish. Ken

Ok Ken,

I think I got it now. Most things come easy to me, but I admit this dope stuff had me baffled. I probably have been reading to much into it.

I'll shoot you a picture of the plane so you can see what I am up against.

Ron