you have to hold it really close to the ski and keep the flame as small as possible. i usually do two coats too, especially for big gouges. basically, just keep the flame small, only blue flame and no orange cause that's where the carbon comes from
It would be a good idea to hold your file close to the flame to prevent that.
'I would be embarrassed to constantly complain about my life considering all the freedom and opportunities we have today. People that can't find anything they enjoy in life simply aren't giving it a real try.' ~Nick 311