Lots of sharp straight edge razor blades then.  And yes, they "gum" quickly.

I stopped using clear monokote on the ailerons and elevators when I had the film "blow out" of the hinge gap during practice up at Weak Signals.  Rather than fold IN to the gap when it closed, it folded OUT in flight...adding significant trim in the process. One minute I'd need 7 clicks of  right, the next 7 click back left.  Thought I had a bad servo until I landed and luckily saw that the hinge piece of monokote was sticking out.  Changed it to blenderm at the field and never looked back.