I bet a person could get more miles out of by first sanding, puttying the voids, sanding smooth, then primer and then a super gloss enamel coat on top, like aircraft quality paint. I bet you could reuse them indefinitely that way.
In fact it is rather difficult to get papercrete to stick to plywood. There is no problem using it in this application and removing it later. I have peices of plywood that have been used many times. Eventually it warps and delaminates but with the price of new plywood these days it feels good to get a lot of uses out of it.
__._,_.___