why not mix fabric medium into your acrylic paint?
I don't know if putting sizing on the banner would be good if you're going to be manipulating the fabric a lot because it might start to crack. canvases are pretty much never folded so a sizing/base coat works for them.
I'd probably also seal it after it's painted with a clear coat. I'd imagine if this banner is hanging out in sunlight a lot, it'll get a fair amount of UV damage. maybe like what they use for outdoor furniture.
The banner is pretty big and the lettering will be too, so it's very visible from the street if I hang it as part of my backdrop (which is inside my tent, and in the shade). Only in desperation would I hang it outside. But if I decide to do that, would that be an acrylic clear coat?
yeah, I'd spray it instead of painting it on though. you want it to be thin so it can stay flexible. maybe there's an acrylic clear coat made for fabrics?
Probably good idea to prevent flaking of the paint. I suppose acrylic will stay flexible on the polyester cloth when rolling it up over and over? I wouldn't want to fold it after painting, because it's always got creases that way.
the fabric medium is what makes the acrylic paint more flexible so it doesn't flake or crack.
your best bet is to do some testing samples. I haven't done a banner like this myself so that's what I'd do first.
