Go to www.jenkinsslate.com it will tell you all you need to know even how to re-roof. Video's an all.
One thing you will need that it the nail ripper the slaters use to remove the un-accessable nails. Slide the ripper UNDER the broken bit till it hits the nail slide past the nail pull back inline with nail pull down when you've got the nail hooked whack the flat of the ripper with hammer to chop the nail do same with other nail.
good luck Doing mine in hot laid felt flat roof. My roof thinks it's a shower.
bob
September 2011