It's a relatively soft plastic and I don't think you can realistically build a uniform, good-looking layer that's 1/8" thick, if that's what you mean. If you need that thickness, high hardness, and nice appearance, I think your best bet is just a sheet of glass or acrylic on top.
It can be used as protective varnish, but that would be a very thin layer, probably 0.1 mm or something like that.
Does it not level from gravity like other resins?
It's solvent-based, so it won't set well in thick layers and it will shrink significantly as the solvent evaporates. You can do thick layers with solvent-free thermoset resins such as epoxy, but epoxy will yellow over time.