"Walter R." wrote in message
For a neat installation and in order to provide for some expansion, I
will need to undercut the fireplace hearth by 1/2" so that I can slip the
ends of the planks under the stones.

http://tinypic.com/view.php?pic=48zmrsh

I have a 4" electric grinder. Will that be suitable for cutting a 1/2"
undercut into the rocks? What kind of blade(s) should I use? I bet this is
going to be a very dusty affair!?

You cannot imagine the amount of dust. Considering the location, the entire
amount of material removed is probably going to be made into dust rather
than cut out. You need an abrasive blade. Just get one because by the time
you cut a few inches, you'll probably see it is a bad, messy, idea. Butt he
wood and come up with a trim strip of some sort.