You need corbels every 2'. Two supports is not nearly enough.

I have steel supports for mine hidden in the wall.

That is the most I have heard, the fabricator told me the two ends should be sufficent. The installer told me that I should probably add one more bracket in the middle for safety. Every 2' would be 5 supports total.
Thanks for the information

I wouldn't cantilever a 3cm piece of marble 13" without additional support. See the link, please.

Here is a link that might be useful: Counterbalance

Trebruchet,

There is additional support. The countertop is supported at the wall (13" cleat), the knee wall it sits on, and a remote leg on the overhang corner.

Our island is 9' and we will have 4 supports for our 3cm 12" overhang.

This post was edited by xc60 on Wed, Feb 26, 14 at 18:49

I just purchased 4 matching supports. I plan to use one against the wall (where the cleat is now), two in the middle of the bar, and keep one on hand for when somebody kicks the leg out or we just get sick of it.
Thank you everyone for your input.

LOL.
Excellent compromise, and a safe one.

There is one problem here no one has addressed: No Pictures

Where's the eye candy?

Haha Christine! You are right. Marble...we definitely need pics.

This picture has a slight view of the bar top. The orange accent under may be going...it was an experiment. backsplash goes up today. we are so excited!

Very pretty, PM. We have the same setup with the stove at the peninsula. We just bult the knee wall and raised bar like yours and love it! We are doing granite, and will have a bit less overhang. We were told that we wouldn't need corbels, but a narrow piece that long should have a base. Do you have anything under your marble?