added picture of rail.

Rail is 1" on three sides.

Here is a link that might be useful: {{!gwi}}

I agree that 3cm should not need sub-base for a 12" overhang, but if the granite fabricator requested it, he will walk away from any problems (of any sort) that may arise, and say they resulted from you not following his professional recomendations. Use a sheet of nice flat 1/2" plywood ( adequate for this and less conspicous than 3/4) I like birch for this, but a GOOD sheet of BC will work , there is no diffrence between AC and BC except for the species of wood for the face veneer, and a large price increase. If you have to use AC you may as well spend the few extra dollars for birch. Cut the sheet so that it is about 3 inches smaller than the size of the granite all around and radius the corners. Get some iron on or glue on edge banding either locally or from a catalogue, and apply to the edges of the plywood, sanding it flush. Prep the exposed part of the bottom of the sheet and the edge banding by priming and sanding. Then paint it with a couple coats of black paint (not high gloss). Now center the sheet on your cabinets and carefully, very carefully, locate the cabinets below so that you can screw the plywood down (countersink the heads). The layer of plywood will look like a buildup of granite underneath.It is crucial that the island cabinets be absolutely flat and level so the installers do not have to shim the granite up to level it. Even so, you may still need to run a small bead of black caulk to hide the joint betwen plywood and granite, and repaint the edge.

Troubleseekral

Thanks for the reply. If I follow your advice my island will be 1/2 taller than my other cabinets. I really don't want to put counters all around the kithcen.

Any thoughts on usings 1/4 sheet of plywood or the shelf brackets the I showed?

I would think that 1/2" ply would be the absolute minimum thickness and 7 ply's being the minimum .Troubleseekeral has good advise, imo.Will 1/2" taller island affect anything? Cosmetically you'll never see it.

Cabinet/counter top shops should have rods that you route in if you wanted to go that route. Out here, that is something the granite companies fabricate into the counter during install.

Plywood supporting an overhang will provide very little strengh.

Stone is plenty strong, but if there is the slightest defect in the stone the first time someone sits on the overhang it can break.
These events rarely are partial and progressing. There is simply a large bang as the stone hits the floor.
Steel rods (adds some strength) or steel angle (adds a lot of strength) with a shallow trim piece to hid it works well.
Simply painting the metal a color near the stone hides it pretty well.
You also need to consider if anyone can actually see under the overhang anyway (short of kneeling on the floor).

Here is what I came up with.

I glued plywood to inside of cabinets with construction

adhesive.
I also use 1 inch lag bolts to get it tight. 3/4" plywood +

1/2 particle board.
Be very careful drilling hole for lagbolt. I used blue

painters tape to mark off 1 inch on drill bit. Just wrap it

around bit.

I then put 10" steel brackets on inside of cabinet.

NExt to drawer was trickiier. I used 3/8 inch plywood, glue on

twice and then had to recess bracket so I would interfere with

the drawer. I also had to cut the bracket short.

The sales guy said brackets were not necessary. The installer

said they were.

The island looks great and you can not see the brackets.

Here is a link that might be useful:

ncdad........ (or anyone else who can answer)...did you notch out anything along the TOP of the cabinet/island, where the granite would lay before attaching the brackets? I'm thinking not since you want it snug against the granite? I assume what little thickness the bracket has is not a problem? Or did the granite fabricator groove the granite for these supports? I'm sure my fabricator is NOT going to do this for me. I could ask, but I truly think they will say no.

Have there been any problems with someone crossing their leg and snagging their slacks? My installer suggested 2 corbels, which I do NOT think will be enough, but more will just be more knee knockers. I hate corbels period. The installer originally said I didn't need anything, but I have 11.5 inches hanging over with a width of 65.

If using the brackets how many would you suggest for a length of 65 inches? Thanks

Thank you

I did what ncdad did and also added three full length steel pieces all the way accross the cabinets and overhang. We notched the cabinet so that the counter was sitting flat and snug. We have a 17 inch overhang with corian, not granite. I painted the steel, bought from HD or Lowes, under the overhang to match my counter and no one even notices them. Haven't had any issues with people hitting them with their knees or snagging their pants.

This is interesting. It looks like ncdad put the metal brackets on the inside. Patches123, can you post a photo? I am having trouble visualizing this...I am trying to come up with a way to support granite as well. Install is wednesday.

patches..I don't understand the "full length steel pieces all the way across the cabinets and overhang". Do you mean under the entire corian? You said you also used the L brackets and notched the cabinets where the brackets sit? Maybe the full length steel pieces are because of the 17 inch overhang, where I only have 11-12 inches?

I assume I would have to notch my cabinets in order for my granite to be level, if using the L brackets? And, that is what you did and why you did it?

mduarte...Please post what you do for support after your install.

I dont understand how corbels do the job that are like 4 inches out (hope that makes sense) and you still have over the recommended max of 6inches unsupported?

I will post, debbie. My install is actually thursday, so I have an extra day to think about this. My installer is saying I need 3 supports. My overhang is 12 inches for 72 inches and then a small side of 36 inches. They are recommending 2 on one side and 1 on the other, but I think I am actually going to put 3. I am contemplating 3 wooden corbels and then 1 metal one in the middle...because it's smaller, no one will knock their knees. Going to take a ride to a local building center this morning and see if the guys there can help me.

We have about a 9ft island that has a 13inch overhang. I have no fear that this would be a problem. Now on our bar we have a 12inch overhang that is only support by like a 8 inch wall. I am a little more cautious about this.

One time my sister strapped her baby (1 year) to this bar with one of those hanging baby seats that mount to the bar or a table. I was not worried about the baby but to test if it would hold my brother in law put his arms on the bar and pushed himself up off the ground with his arms. He weighs about 250lbs. I thought my granite might crack and quickly said "what are you doing"? They baby only weighed like 20lbs.

I know this is not going to help the original questioner posted in 2007 and I sure wish I had found this question back then... But for those of you looking for "THE" answer... hear you go.
The Amastin Company, Corryton TN, has been providing steel support bars in supporting hard surface counters to the East TN market since 1995.
In this particular case, which is a common one, Amastin offers a 31" long x 2-1/2" wide x 1/2" thick steel support bar that would bump and mount into the back of the front face frame, notch and recess flush across the back cabinet mounting strip. This support would overhang 8" leaving it approx 4" from the counter edge making it virtually hidden.
Amastin has the overhang support thing figured out and if you have any questions or in need of custom support advise... Amastin is place to find the answers.

Here is a link that might be useful: The Amastin Company- Steel Support Bars