As a few have mentioned it's a matter of rate. Put it on and scrape it off when you see it reacting, bubbling the surface. Repeat as needed, without letting it linger more than necessary. It's a real good stripper. Follow with acetone to remove the DCM, then with water
. DCM is miscible in acetone but not water
, acetone is miscible in water.
I used the stuff daily for 5 years about 30 years ago at a MIT Chem lab. Breathed it too with no I'll effects...yet.
Common sense is the key with that substance, but it is quite useful.