Martin, I have concerns over your customers choice of covering the body shell with Irish linen and dope. I am not an expert on early aircraft but my understanding is that a doped linen would be used over a very light skeleton frame. As the dope dries and the linen shrinks, it becomes very tight and it is the tension created that gives the very flimsy frame its strength, rather like an umbrella when it is opened.
I assume that the linen would be tacked to wooden frame members and joints laboriously stitched. Irish linen is quite thick material and I would worry about its suitability for going around fiddly areas like the window apertures. On an aircraft it covers quite large, flat areas.
The body shell already has strength and the fabric covering does not need to add any strength. It only needs to be attractive and weather resistant.
What you are doing is exactly what I did when I built the Pytchley saloon. Before I covered it, I made a couple of small plywood covered squares which I covered with different materials. I then left them out in the weather over the winter to see what happened.
I used a thin cotton based material sold as curtain lining, very cheap from Boyes. It is not tacked or stapled to the body shell, it is simply glued on.
Having primed the bare wood on the body shell, I painted sections with yacht varnish and whilst wet laid over the thin material and smoothed it out with a brush. It is not stretched at all. I cut the material oversize and when it came to doing the edges, I trimmed it with scissors and turned it over the frame, securing it with more varnish. Because it is thin, you can overlap the material when you do fiddly corners and it all looks very neat. Irish linen is too thick to get away with doing that.
As you apply the thin material, it becomes almost transparent with the varnish, becoming white as it dries. When dry, I added another coat of the yacht varnish, then an oil based undercoat and two coats of Farrow and Ball oil based eggshell paint (when F & B paint was good, I would use Little Greene now).
Although I say so myself, the result looks very good and the car had instant 'age' and patina that you don't get if you use modern leathercloth. Furthermore, after about 15 years the body finish is like new and extremely durable.
For the roof covering I used Everflex. The shade of blue was not correct so I painted it with the F & B eggshell.
