I am installing my large 78" diameter 1 peice of granite in a brazilian walnut floor. I am planning on leaving a 3/16 gap around the whole diameter for any expansion. does sound right? Is it needed?

You need to leave something for expansion.

I would not bother leaving a gap since it is in the middle of the room. I would probably just glue the granite with Bostiks best or Dritac 7500 .

Ever heard of anyone leaving a gap when they drop in a wood medallion? Me neither.

Saw a demonstration at the NWFA convention in 2004. The template was set to provide a similar gap for a stone medallion. Some wondered why such a large gap after looking over the work when everybody left.

Perhaps that is an NWFA standard. If so, I would be interested in reading the rationale underlying it.
I suppose an argument could be made that since the granite will not compress when the floor expands, some space is needed. My instincts tell me that using a pure urethane adhesive under the insert would make that a moot point.

I don't have any hard opinion on this one. Guidance, anyone??

Is there a finished room under the medallianor no? I took a class with the nwfa and a gentleman from oshkosh was there demonstrating on how to put one in. They did say that the template provided with the medalian provides for a tight fit. I think that a gap around would look bad. I also dont think you should glue it. Leave it out for the sanding and install it after the sanding. Screw it tight to the floor from underneath. If you have to glue it, plan for, if you want, to remove it at a later date for a resanding. Just my opinion.

Tony

I talked to Tom from OshKosh flooring, he is the one that said you need atleast 3/16 gap when installing the granite medallion.
I know with wood medallions they are tight fitted, I just don't understand why a gap is needed with the granite or any stone medallion.
BTW, we caulked the gap with a black silicone that matched exactly to the granite. you can not even see the difference. I feel good knowing that there is some type of expansion gap with such a big piece of granite thats glued down.

There is an article in this months hardwood floors magazine explaining just that. A granite inlay. Check it out.