As NAV stated, drywall products are meant for INTERIOR applications. I know there was/is a sand type finish (additive) available that I'm sure can be mixed with exterior paint to suit your need. HOMAX makes a lot of interior type texture finishes. Not sure if the one you're looking at would be suitable or not. Mixed with the proper paint it may be ok. Check their web site and see if they have information there to answer your question or an 800 number you can call for advice....
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