How do I undercut a stone fireplace?


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?picHzmrsh
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
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Walter
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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.
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Thanks, Ed
Would a 4" diamond blade reduce the dust and cut a thin slice? Can I reduce the dust and enhance the cutting action by having my wife cover the area with a water mist/spray?
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Walter
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Unless you have a steady trickle of water running on the blade it is going to make dusst like you have never seen. If you do have water running on it, you will have one muddy mess that will dry to a grey powder everywhere it runs. BTDT but fortunately outside. Take the advice given above and use a trim strip to cover the gap.
Harry K
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wrote in message

contract that much, put a kerf in the trim strip so it rides over the flooring, with a bullnose on top to avoid splinters. Scribe the fireplace side to match the stonework. Having a trim strip 1/4" taller than floor will barely be noticable. Trying to put a kerf in the existing stone is just asking for trouble.
aem sends....
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Rent a jamb saw from the local shop. Many places won't rent to you if they know you're doing a fireplace, so keep looking. Use two shopvacs, one on each side of the blade. This will keep the mess to a minimum.
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wrote:

You have gone to all this trouble to get petrified wood and you're going to grind parts of it away. What if something happens like a chunk of it from the top half inch breaks off. It seems to me that could happen with anything, during the grinding or later, (and especially with petrified wood which might not have been a perfect log before it petrified. My firewood has cracks in it, some cracks with air in them, and others that don't appear to be cracks, but I know one piece of wood is not attached to the wood next to it.)
Why not get a profile gauge, or whatever it's called, the thing with the big set of parallel pins in a clamp, and trim the fresh wood to match the petrifed wood. If it doesn't come out right, you can get another plank. If " butt against" mean it is the ends that abut, you can just cut a couple inches off the plank and start again.
FTR, I've not worked with petrified wood (I'd be too scared) and I've never used my pin thing, even though I have one, and I've never done a floor. Just consider my post a suggestion. (I'm watching "24" and it makes me more assertive. Well, actually more violent, but all I have is my keyboard.)

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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/assets/product_images/9527PB_l.jpg
http://www.diamond-saw-blades.com/images/ddmpho~1/Tuck%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.

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Thank you for your advice, Cliff
All the pros I talked to recommended the undercutting method. The way you describe it, it should work. My 4" angle grinder sits 1/2" off the ground and should give me the perfect height and depth of cut.
What concerned me also was the need to allow for the expansion of the hardwood floor. The best way of doing this is to let the wood move in the undercut under the stones.
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My only concern is that your 4" grinder will cut deep enough. That's some pretty rough stone.
If you have never cut stone like this with a diamond blade you will be surprised just how smooth it cuts. You may think that you aren't cutting at all. Just don't bind the blade or its going to kick and chip.

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