If you don't have access to a sand-blasting cabinet, you might be able to loosen it by prolonged immersion in methylated spirits or cellulose thinners. Both can be used as dilutants when applying (I find thinners best when spraying it on, but meths best for removing it). But Brian is right - blasting is the surest & quickest method.

ATB
Information
Warning: This is a relatively older thread
This discussion is older than 360 days. Some information contained in it may no longer be current.