Spary painting balsa?

[John Fairbairn]

I am building a DFS Habicht and have finally got to the stage of spraying it. I have never actually sprayed, or really painted a balsa model before and after 2 coats of rattle can acrylic grey undercoat it shows the grain and the tiny slots in it.

I did a very light rub down with 400 wet/dry used wet but the surface is still pitted with the grain 'slots'. Would it be a better idea to paint it with cellulose sanding sealer before the spraying?

I actually work with wood a lot as I am retired and my hobby/passion, besides RC gliders, is wood turning and I have the sanding sealer for that. I realise that there shouldn't be too much paint or sealer applied because of the weight it adds, but any ideas would be gratefully received.

[chris williams]

John, this is a subject that would take a novel the size of War & Peace to cover...! First, you need to cover the fuselage with something, either an iron on fabric or glass cloth and resin before painting. Then you have to decide what to cover the wings with: fabric or film. A lot depends on where you intend to fly it; slope or aerotow?

[John Fairbairn]

I tried War & Peace once and gave up on it after a quite short time, but I did read A Brief History of Time by Stephen Hawking !

Seriously though. The open works are covered with Ceconite 104 and fixed with Balsalok so it would make it difficult to cover it with any other type of film or glass on the non Ceconite parts. Plus, I have already sprayed the tailplane with acrylic undercoat. That's when I realised that balsa doesn't give the same sort of finish as the wood that I turn on my lathe!

Would the old fashioned cellulose dope be better than sanding sealer I wonder? It's one of your early plans with the Frise ailerons and the fuz is 1/32" ply covered with 1/8" planked from the back of the cockpit forward.

I will be slope soaring almost all of the time on the hills around the Stroud area with the South Cotswold Soaring Association, so a nice tough finish will be better. I haven't ever done any aerotowing. I think it would terrify me!

[Peter Balcombe]

John,
As Chris W has said, the fuselage needs to be covered in something such as fabric or glass cloth to suit the full size surface/landing environment. The fabric needs the weave sealing with dope or similar before painting, whereas the glassed surface will take paint directly.
For Ceconite covered wings (as for the old Solartex covering), just seal the weave with dope & that can be painted also.
Just make sure that your paint is compatible with the covering sealant.

These techniques have worked on the various builds over the past few years, including all of the 1/3 scale prototypes built for Cliff Evans including the T21 & ASK13 to name the 2 latest ones.
Peter

[John Fairbairn]

Thank you Peter, I will see if I can get some dope?

What would you recommend? I am looking at Eze Dope on Amazon at the moment. It's a non celulose dope?

[Peter Balcombe]

Hi John,
I’ve never used the Eze dope but I guess it should work - just a water based alternative? This is certainly less smelly & probably compatible with most paints.
I normally get cellulose dope in larger (0.5L tins) & thin it a little for application with a 3/4” or so brush.
The cellulose dope comes in shrinking (as used with tissue etc. which slackens when wetted) or non-shrinking variety. With Ceconite, I use the non-shrinking type as the Ceconite can be taughtened if necessary with gentle heat from an iron afterwards.
Peter

[John Fairbairn]

The Eze Dope I was looking at is a shrinking dope and the Ceconite has already been done with my film iron so I don't want that or it will either pull it off of the frame or distort it!

I will see if I can find some non shrink cellulose dope tomorrow? In fact as far as I can recall the job of the dope is to fill the grain on the wood and the weave on material coverings. Is that correct? Because if it is then my cellulose sanding sealer would do the job perfectly?

Off subject for a moment I am not getting emails letting me know that I have replies even although I have the box ticked. Any ideas please?

[Peter Balcombe]

John,
My take on sanding sealer is that it is basically a cellulose dope, loaded with particles to improve its filling ability.

Can’t help on the notifications issue, but maybe Cliff will be along to advise.
Peter

[John Fairbairn]

I have got some non shrink cellulose dope from Leeds Model Shop and the smell of pair drops takes me back a lot of decades! I was surprised to see on the tin to thin it with cellulose thinners as I had read that these dopes should have all sorts of expensive thinners chucked in them.

I bit the bullet and tried it out on an elevator then as it looked good I have now done most of the control surfaces just the stbd ones to do. Then on to the port wing.

For the fuz I may well cover it with doped tissue?

[Peter Balcombe]

John,
You will probably need to go over coated wood areas with fine sandpaper to smooth off as the dope with raise the grain - but I’m sure you are well aware of that from other woodwork jobs.
The edges of the Ceconite will also benefit from similar treatment. I usually tidy up edges using a fine sanding block, reseal the edges & then go over the edges with a hot iron to smooth everything off.
Peter