Finishing sheet balsa surfaces part 2
Finishing balsa presents several unique considerations:
First, water and water based finishes on bare balsa results in warped balsa - not good.
Second, how to fill the grain to get a smooth surface.
So what has been the solution for modelers so far on larger planes?
Apply epoxy or polyester resin directly to the bare balsa to fill the grain and strengthen the surface followed by painting.
Cover the balsa with fiberglass cloth, or synthetic fabric attached with epoxy or polyester resin then paint.
Cover the balsa with silkspan attached with dope then painting.
The first two choices are too heavy for small planes, plus there are compatibility issues with certain commonly used paints when applied over polyester resin or epoxy. The third choice comes closest to what I am looking for but still comes out a bit heavy due to the fact that the silkspan requires a good bit of dope to seal and fill the grain.
I need something lighter!
The solution is to cover the sheet balsa with modeling tissue then painting the covered surface with fuel proof paint.
Advantages to covering with tissue:
Cost - tissue is cheap!
Tissue is already pigmented - takes less color paint to cover.
Light weight
Tissue is easy to apply if certain guidelines are followed.
Tissue has a very tight weave that fills and seals easily.
Tissue adds significant strength and stiffness to balsa.
Color tissue with a clear finish looks great by itself, don’t need color paint!
Tissue can be used for color trim
Tissue applies easily to compound curves
By now you are likely thinking what are the downsides to tissue? First, tissue is delicate, especially when wet and therefore may be difficult to apply. Second, there is a great variety in types of tissue, some apply easily while others are nearly impossible to apply. Third, applying tissue WILL take a bit more time and effort than applying iron on finishes.