I bought some large pots at Sam's Club a couple of years ago. I thought they were some type of ceramic since they are heavy (but not as heavy as clay pots). The largest one was left on the patio over winter and the finish - which turned out to be some type of paint over what looks like plaster - is cracking and falling off in chunks, taking the plaster-like stuff with it. It hasn't revealed what's under the plaster yet. It will definitely require a coat of paint over it (I have some exterior latex that I can use) but what can I use to stabilize and weatherproof this plaster-like stuff? I have Kilz, Bullseye and regular exterior primers but I don't know if I need something different. Anybody have any ideas?