What was found
(CAN) THE AIRCRAFT HAS A BLACK MATERIAL BONDED TO THE AIRCRAFT BELLY SKIN INTERIOR TO PREVENT OIL CANNING.SEVERE CORROSION WAS FOUND BETWEEN THE BONDED MATERIAL AND THE SKIN. IN SOME AREAS THE CORROSION EXTENDED TO A DEPTH EQUAL TO HALF OF THE SKINS .032 THICKNESS. THE SKIN WAS REPLACED. OTHER SKIN AREAS ALSO REQUIRED REMOVAL OF THE BLACK MATERIAL AND REMOVAL OF SURFACE CORROSION CARRIED OUT. A REVIEW OF THE AIRCRAFT IPC COULD NOT FIND THIS ITEM. THIS UNKNOWN BLACK MATERIAL WAS CHECKED WITH A MULTI-METER AND FOUND TO BE CONDUCTIVE SUGGESTING THAT WITH THE PRESENCE OF MOISTURE ELECTROLYTIC CORROSION COULD RESULT.