I have a 12' X 30' screen porch which has a greenboard ceiling. Over the years several seams have started to split and the taping has come loose, probably as the result of minor shifts in the construction (the original porch, 12' X 20' was built in the '60s and the rest added on in the '80s). The board itself is in good condition. Can I use a troweled elastomeric putty to replace the original tape and drywall compound? Any suggestions out there?