We frequently come by cards and covers which have tear damage repaired with plastic tape.
Serious trouble is certainly at hand with such items.
You may think, and probably correctly so, that further deterioration of the item can be avoided by removal of the plastic tape. The best advice in dealing with the repair of items mended with plastic tape is to seek the aid and services of a professional conservationist. Cardboard is another item to be kept well away from our philatelic materials. It is generally highly acidic, and the chemicals in cardboard are rapidly transferred and hasten destruction. If you require a rigid support of a philatelic item, use an all-rag type of board.