Question about Granite overhang for bar top

14 years ago

I heard recently that there are some granites to avoid for a bar top since they could break. My overhang will be 12 inches and I know that I need to have supports. However, I was told to stay away from the granite with the mesh backing for these areas. Is this true? I was also told there is two different types of mesh backing.

Thanks for your advice.

Susan

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Comments (12)

nursetammi
14 years ago
My granite was just put in on my bar. My bar hangs over 3 inches past the supports (corbels) on each side and 9 inches past the support in the middle off the support (corbel). The whole bar at the longest part hangs over 15 inches in the middle(granite is 22 inches long there)and 10 inches on the sides (granite is 16.5 inches long there. These are quick measurements but I thought it might help to see how much hangover I have past the supports. No mesh on my granite.
svwillow1
14 years ago
We have a mesh backing on our 3 cm granite, 10" overhang, no supports. Everything fine. I was told that the mesh is there more for the slab yards and fabricators to give the granite some extra support in shipping, not for when it is used as a counter top. In fact, our fabricator polishes a portion of the underside and in the process, removes some of the mesh backing.
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azstoneconsulting
14 years ago
ANY stone - regardless of mesh backing or not - that has an unsupported overhang
of 6" or more if it's 2CM or 10" of overhang if it's 3CM - REQUIRES some
kind of support from underneath - such as a corbel.

There is a product that is available from Chemical Concepts that is a
support plate that does the same thing as a corbel, but is far less noticed
from underneath, and will do the job too.

I have been doing Natural Stone for 24 years, and ALWAYS require corbels
or some type of support from underneath - REGARDLESS of the stone
(mesh backed or not).

The mesh baking is usually applied to stones that have fissures and that are
prone to opening up, so remember the rule of 6 & 10:

ANY unsupported span of 6" or more (if 2CM) and 10" or more (if 3CM)
HAS TO HAVE SUPPORT FROM UNDERNEATH - or else the stone could
crack or break if "stressed" - like having someone sit on it, or apply
flexion or weight to the assembly.

I look at failures of other fabricators all the time, and this is the number one
way that they could have been avoided.

just my .02 cents worth as an expert in this Industry..........

HTH

kevin
Cloud Swift
14 years ago
Our overhang is 15" with 2 cm granite. We didn't want anything in the way underneath so we supported it with 3/4" plywood. For extra strength, there are 5 steel bars routed into the plywood:

With that under it, I think any stone that would work on a countertop would have enough support. It is quite strong and stiff. The laminated edge of the granite covers the edge of the plywood.
azstoneconsulting
14 years ago
Cloud Swift:

Plywood (IMHO) alone is NOT enough to support any overhang more than 6 inches in
2CM and 10 inches in 3 CM. The steel will be doing the lion's share of the
support of your assembly..... Just make sure no one sits on the overhang!!!

kevin

Here is a link that might be useful: Chemical Concepts - Counterbalance Plates & Supports
nursetammi
14 years ago
Kevin,
Is there a rule how far the granite can extend passed the corbels?
azstoneconsulting
14 years ago
Nursetammi:

Yes - it's the same as the rule of 6 & 10 -

here's an example: Let's say that you have 2CM stone and you want an 18 inch
deep overhang - you'll need to have at least 12 inches of the total span supported
by either a corbel or a Counterbalance Plate from Chemical Concepts.

here's another example: Let's say you'd want a 15 inch overhang span and your
stone is 3CM - in this case, you'd need to have at least 5 inches of this total
span be supported by a corbel or a Chemical Concepts Counterbalance plate
- so that no more than 10 inches of the total span is un-supported.

Dos that make sense? Just remember that the amount of unsupported span
of the stone depends on the thickness of the material - 2CM means no more
than 6 inches can be unsupported of the total span, and 3CM means that 6 inches
of the total span can be unsupported.

Also - remember that 2CM stone should ALWAYS have a sub-top of 5/8"
PLYWOOD - preferably ACX (sanded one side). IMHO - Marine grade plywood
is overkill - unless the assembly is going to get wet much of the time.

Plywood - in and of itself - does not add structural rigidity to an overhang -
it provides support when installed over cabinetry, but plywood WILL flex in an
overhang application if not supported by corbels, structure or counterbalance plates....

hope that helps ya

kevin
ccoombs1
14 years ago
I tried to get away with just using flat steel plate to support my granite and even though they were nice and thick, once I screwed them down they still flexed. So I took the plates back to work and had the bottom gusset added to make them more like the counter-balance plates. They work great now!

Another big thing to consider is the structure that the support plates will be attached to. If these plates are screwed into the top plate of a pony wall (like mine are), the weight of the granite will try to twist the top plate of the pony wall. Make sure that top plate (2x4) is well attached to the studs below it or it may try to separate from the wall.
azstoneconsulting
14 years ago
Ccoombs1-

What you are showing is an EXCELLENT method of supporting your upper bar!

The vertical "gussets" that you added to the underside of the flat plates of steel
are what really does the majority of adding structural rigidity to the assembly,
and this in turn, will support the stone much better than just ply wood.

I wish that more people would do this kind of support for their upper bars and
general overhang assemblies. If they did, there would be far less failures
of these kinds of applications. This would - however - affect my income,
because there would be less failures for me to go out and inspect and tell
the unfortunate homeowners what their Fabricators (or in most cases - their
"pretend fabricators") did wrong and how their "do over" work should be re-done...

all in all - GREAT JOB CCOOMBS1 !!!

kevin
ccoombs1
14 years ago
Thank you Kevin! I am happy with the result. The supports are not noticable and they hold the bar up quite nicely. Sometimes working at a metal fab shop has it's advantages. I just tell them what I want, and they make it for me.

Cindy
anny-2009
14 years ago
What useful information!
However, when we use flat steel plate to support granite, does the thickness affect the balance of the granite? It can be crack or chip at this point?
If I understand well, 3cm doesn't need plywood?
ccoombs1
14 years ago
Flat steel plate usually has some flex to it. I think my steel was 3/16" thk which feels pretty darn strong, until I atached it to the pony wall and then put some weight on it. It flexed a little bit. Granite does not like to flex. The steel gussets I put on my flat plates turned the flexable steel into something strong enough to park a truck on! Angle, square tubing or "t" bar (like I had made) are all very strong. flat plate is usually not strong enough to keep from flexing.