Granite Experts: Overhangs and Curves

14 years ago

Things are starting to get real on our remodeling project - hoping to have signed contract with our GC tonight. Today, my specific question is for the granite to go on the upper portion of our island. Right now, we're looking at Russian Sable from Arizona Tile, and they've found us slabs that are 130 x 62 (although we haven't seen those slabs yet). We're planning on a simple edge detail (1/4" radius or eased).

Here's a drawing of what we expect the finished kitchen to look like:

For the upper countertop on the island, here are the measurements (these came off the original drawing, they may change by small amounts). The gray shows where there's cabinets/structure underneath, and the white is the overhang:

I guess I have three questions right now:

1. Are these curves hard? While we haven't gotten an exact breakdown, our GC is telling us that this will add about $1000 to the total (it's hard to tell if this is just the SF charge, but I don't think so).

2. Assuming we go with those large slabs, would you make this top out of a single piece, or is that too big to handle? If you would seam it, where do you think the seam would go?

3. For the large overhang at the end, we're looking at having "hidden" metal supports. I'm thinking that we may reduce it a little bit (maybe 18" overhang). Does anybody see any issues supporting this overhang?

What other questions should I be asking?

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Comments (5)

dimond
14 years ago
Hi, I am not a granite expert - but I am a Civil Engineer. Here is my response based on the little I know about granite:
1 The granite fabricator can likely do whatever you can draw - but that does not mean it will not crack. $1000 seems reasonable to me.
2. You likely may need to seam this perpendicular to the 98-7/8" dimension. Unless you have some incredible support system the 20" overhand is likely going to crack. I have seen many homes where the cracking is visible (albeit small) where there are strong supports and the overhang is 12". With seam as noted above and loosely anchored supporting plywood atop 5" pony wall - the granite slab will rotate at seam and not hopefully not crack. The seam may need silicone caulk as it will open/close somewhat.
3. Your proposed overhang atop a 5 inch pony wall seems very unrealistic and sure to crack (if single slab). I would recommend that you work with your granite fabricator to work out support/seam/overhang issues/geometry. Further, try to get some guarantee/warranty against cracking (maybe for 2 years), as this will give you some indication on the sturdiness of the fabricator support/installation design. A great forum site for technical granite issues is stoneadvice.com, as it is frequented by granite fabricators that specialize in such matters as you may be asking; however, your lifeline in this matter is likely going to still be your granite fabricator.
The above represent my 'opinions' - not expert advice. Good luck!
azstoneconsulting
14 years ago
I AM an Expert When it comes to Granite Fabrication & Installation -

THIS is what you need to remember when dealing with overhangs:

"The Rule of Six and Ten"

ANY Natural Stone Slab Countertop assembly that is 2CM thick with an unsupported span of
6 inches or more MUST HAVE CORBELED SUPPORT

example - IF your overhang is 18" total - you'll need corbels that are a MINIMUM
of 12" deep.
Along WITH THE CORBELS - You should ALSO HAVE 5/8" subtops from PLYWOOD - ACX grade or better.

ANY Natural Stone Slab Countertop assembly that is 3CM thick with an unsupported span of
10 inches or more MUST HAVE CORBELED SUPPORT - NO SUBTOPS ARE REQUIRED
FOR 3CM THICK COUNTER TOPS

example - IF your overhang is 18" total - you'll need corbels that are a MINIMUM
of 8" deep.
Again - NO Subtops Are Required for 3CM thick countertop stone

Spacing is best to NOT exceed 16 inches apart in either case.

I'm going to post this at my NaturalStone101.com website - I'm getting
REAL TIRED of typing this out every couple of weeks........ HA!

hth

kevin

Here is a link that might be useful: Corbel Wizard - Read the text box in full on the right
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hgluckman
Original Author
14 years ago
dimond: Thanks for your engineering perspective. I will definitely be seeking advice from the fabricator (haven't met them yet).

Kevin: Thanks for repeating that again. I neglected to say that the slabs we're looking at are 3 cm. We're thinking of using something like the Counter Balance supports (that I believe you've recommended). Do you have any opinions (there's a loaded question!) on my other questions?

Thanks

Howard
hgluckman
Original Author
14 years ago
Bumping to see if anyone else wants to chime in....
azstoneconsulting
14 years ago
Sorry - never saw the response there....

The Counter Balance Plates are super and I recommend them all the time.

They are available from Chemical Concepts (link at the bottom)

Answers to your questions:

1. No - unless your Fabricator is of the "pretend" variety (watched a few DIY
shows and now he thinks he's an "expert"... HA!) Any Fabricator that is worth his
salt can do what you are proposing with the radius work - If you are in PHX -
there's some really good contractors that I would recommend.

2. IF your slab is big enough - you could make the top in one piece. Since you're
size of the piece is 122 1/2 - I'd be looking for a 124" long slab (there ARE
slabs that big that are available) AZT is a PREMIER supplier with a HUGE
sourcing structure, so depending on the stone - you may find a slab that
will work perfctly.

3. The CC Counter Balance PLATES will work for what you are proposing

hth

kevin

PS - Say "HI" to the folks at AZT for me - THEY ARE REALLY GOOD PEOPLE!!!
I bring my Training Classes there to the Tempe HQ each month for AZ School of Rock.

Here is a link that might be useful: Chemical Concepte - Counter Balance Plates

Granite Experts: Overhangs and Curves

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Granite Experts: Overhangs and Curves

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