I think I'd consider some concrete board as a backup. Maybe some
sheet steel behind if it is to be there for a long time.

I don't have one, should consider it. Hard material would grind through
while a saw requires M42 or magic to cut.

Some just work hardens as you saw.

Martin



A chop saw is fairly inexpensive at HF, blades are cheap at the same
place or on Ebay. And its a ****load faster than your recip saw. Much
much faster!

http://www.ebay.com/itm/Metabo-14-Me...-/351572313826
(note the name?)

http://www.harborfreight.com/catalog...ult?q=chop+saw

The single biggest issue with a chop saw..put a piece of masonite,
plywood or sheet steel on the wall behind the saw so the trail of
sparks doesnt catch stuff on fire.