Help with 30+ year old mud

[PYB]

Anyone have a tip in how to remove a 30+ year old mud? Got in a restore and found a spot where the mud is about 3/8" (its in good shape no big checks or cracks couldnt beleive it)Some of the stuff is light gray and some is yellow. Any ideas. A DA w/80 will barely touch this and I would like to get it off to see what I really have to work with

 

[alienboy]

Sometimes you can get aircraft stripper to soften up that old mud. Other than that, try 60 grit on that da.

 

[rex]

Whip out the ol' grinder with a 5" 24 grit disc,that'll chew it off fast.If you end up finding a nice crease or the old dent puller 'volcanos'I put a 24 grit Roloc on my little 3' pad on an angle grinder and eat the rest off.The remainder I hit with a sandblaster to hit bare steel to start over.If you don't have either just eat off as much as possible and take a blaster to it,mud comes off a little slower than paint but it'll chew it right down for you.