I think as long as it’s thin enough to fill the cracks in the glass it should work ?A gravity feed gun with a large orifice will work fine, but I was thinking that just brushing it on should work fine. It will need a flow agent even if it is sprayed, so maybe even thinning it a bit and pouring it on might work.
I agree on the experiment part. I'm not convinced that the exterior surface needs to be glass smooth.