What kind of support does a 15 inch overhang on an island require?

[Hassin Bin Sober]

11. I had one granite installer refuse to warranty anything unsupported over a 12 inch overhang.

That required the corners to be rounded so the radius never exceeded 12 inches.

The client didn't want rounded corners OR corbels/supports so we opted for steel re-enforcement bolted to the cabinets..

We had a piece of 1/4 inch steel fabricated to cover the whole island piece including the over hangs - but held back 4 inches at the overhangs so you can't see the steel edges. We had the installer epoxy the granite to the steel.

I had another granite installer not flinch at a 12 inch over hang - which means the corners were like 15 plus inches (this was a peninsula with over hangs on only two sides). This a was a less vein-y type of granite.

It also depends a lot on the type of granite.

The more veins in the granite the weaker it is. In the first case I mentioned, the granite was very vein-y. Even with all their care, they still broke the sink-run piece when installing it. The piece bent like a piece of wet toast. The client happened to witness it and that's one of the reasons he demanded extra support for the island.

Granite will flex a lot - until it doesn't - and then it breaks.

Granite installers will sometimes epoxy in steel rods in weak spots (around cutouts) so the piece will not break during transport/installation. The rods have been known to cause problems later if they get wet and rust. Rusted metal swells - this can crack the granite. It's best to use stainless steel rods.

A lot of installers now save time/labor re-enforcing the slabs by transporting them in clamping racks made for this purpose.