First off scribing won't work. It will leave a jagged edge and will never
look right.

You need a right angle grinder with a dry cut diamond blade.

Like these

http://www.bobcometal.com/bobcomall/...s/9527PB_l.jpg

http://www.diamond-saw-blades.com/im...ck%20Point.jpg

I don't know whether a segmented or continuous rim blade will work better.
I think a segmented blade cuts faster but rougher.

In order to get a good straight cutt you need to make some sort of holder
for the grinder that slides along the floor that can hold the blade the
requierd 1/2" above the floor.

Its going to make a ton of dust, you may want to make a tent out of sheet
plastic and hold a shopvac hose close to the grinder.



"Walter R." wrote in message
.. .
I am putting wood planking in my living room. Some of the planks will butt
against the fireplace hearth, which consists of petrified wood set in
mortar. The area where the stones meet the concrete pad is very irregular
due to the irregular shaped stones. The floor is a concrete pad.

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!?

Any advice appreciated

--
Walter
www.rationality.net
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