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I'm bending cedar shingles to set on my rolled edges of my roof. I've found a system that works. Sort of..
Soak the shingle in the lake, then go swimming that night and recover them when I didn't put enough stones on them to properly weight them down ;-( put more stones on top of them and go swimming a few days later when really big boats kicked up some waves and nearly a whole square was floating off..
get some big plastic tubs and soak shingles in for about two weeks. ;-)
now put a shingle in the microwave for 4 minutes and then into the stem bending form for 4 mutes with an extremely heavy weight (64 pounds) with the proper radius on it and in the form. Pull out of the steam box and quickly run it up to the edge of the roof and nail it top, middle, and bottom, who cares if the stainless steel staples show because otherwise the shingle will slowly curl back up.
Hopefully at some point I'll be able to remove the staples from the bottom once a few years have gone by and they've learned their place in life..
Now these are for regular sixteen inch shingles not shakes.. I couldn't get shakes to bend no matter how long I steamed them. (I TRIED UP TO 8 HOURS) around an 18 inch radius.
now the edge of my dormers and my tower all have about a 6 inch radius which I simply cannot figure out a way to bend around.. I lose about one in 5 shingles with the 18 inch radius even though I keep them all around 4 inches wide.
I saw a few articles in FINE HOME BUILDING showing it done but none of the articles had details.