I thought I'd post the first two pictures in case they may help someone else. The Crain 820 nicely undercut the majority of my stone and mortar fireplace hearth. Thanks again to those who advised and guided me as to how to tackle this part of my flooring project.

The 820 easily slid in under most of the protruding stones giving a minimum of 1" or more of undercut expansion space under the hearth. In one spot though, where shown in Photo 1, even with the guide removed and attacking this space from all angles, the motor housing bumped up against a protruding stone and I was only able to undercut about 1/2' in depth. As I would be approaching the hearth from the middle of the room I felt the 1/2" depth of cut would be insufficient to slide the scribed (cut to fit under the hearth) board in under the hearth before installing the last full course before the hearth and then slide it back out after installing the last full row. My solution was to reach in under the hearth with a masonry drill making a series of deeper holes as shown in the second photo and then carefully chisseling out the shallow undercut to a full 1" or more. This worked well and accomplished what I intended. I hope it might help others as well.







The third photo above shows my template (on the floor in front of the hearth) for cutting the board that will slide in under the hearth as described above.

On the other side of the room I found that shorter ripped boards at the wall worked better as they were in most cases easier to pull back and fully engage the tongue of the last full width boards. In some cases the middle was tough to pull back where I had to punch through a bit of drywall to lever the board back out fully. On the wall this will be covered with baseboard so was not a problem. For the fireplace, I have selected and saved a nice straight long board wider than the hearth that I intend to scribe and cut with the template shown. This will allow me to access both ends of the board to pull out into the last full width course. This board is almost 7' long. Now after learning what I did along the opposite wall I'm wondering if this one long piece may be more difficult to work with than two or more smaller scribed pieces. I'd appreciate any suggestions on this. ZT

I think you have handled this as well as anyone could. And better than most would have. That is one massive, rustic looking hearth. Honestly, I would have considered redoing the hearth and surround before going to the trouble you have gone to. But that's just me. The hearth's rustic nature matches the wood flooring quite well. Uh, shorter boards will be easier to maneuver into place against the hearth.

Thanks again Gary! I do appreciate your replies and advice.

When you have a little time please have a look at my other recent post titled "As I approach the stairs".

I know it's a long read and there's a lot of questions in there but I'd appreciate your input and any suggestions you may have.
ZT

Just responded.