Overhang

Clean · May 12, 2018 12:06 am

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The overhang in the kitchen benchtop is 400mm. Does it have a risk of breaking? I asked metricon to change it to 300 it seems they missed it.

StructuralBIMGuy · May 12, 2018 7:52 am

clean
Brittle material cantilevers should be reinforced but then again they do crack
Check to see if the local manufacturer has a warranty?
Here's an extract from Caesarstone Warranty
Quote "(xii) Cracks in the material are not a material fault; cracking is the result of externally induced mechanical stress on the material after installation. The most likely causes are settlement or movement, excessive weight being placed on the tops, such as standing or sitting on them. Heat, as explained in section (viii) may also result in a crack. Any crack emanating from a sink cut-out, cook top cut-out or “L” shaped cut-out is also not covered under this warranty, these are not caused by any fault in the material. Chipping is not a material fault, it is normally the direct result of an impact to the edge of the benchtop surface, as such it is not covered by warranty"
goodluck

r_13 · May 12, 2018 11:41 am

I found a Caesarstone NZ design guide which shows on page 11 that overhangs should have supports installed beyond a certain length overhang, which depends on the thickness of the slab material.

Quote:

Overhangs

An overhang is a surface that is not directly supported by a construction underneath, eg. a surface that extends past the edge of the supporting cabinet for use as a benchtop. Extra overhang strength can be provided by laminating another piece of Caesarstone of the same colour slab underneath the benchtop surface. In this case, the bottom slab is attached back to back underneath the surface so that the polished surface is exposed underneath the slab.
The permitted overhang dimension must be determined by a professional. It is dependent on a number of factors, such as:
• The complete length to width ratio of the surface relative to the length and width ratio of the overhang.
• Whether the overhang is supported on one or more sides by a wall or other supporting fixture.
• The table below provides approximate guidelines for support required for overhangs.

Supports are dependent on the application, if the overhangs will be subjected to high loads, then supports should be used regardless of the recommendations.

Elsewhere, I also saw a recommendation for natural stone which was about 2/3 of the overhang values for granitestone or Caesarstone as it is more brittle.

chippy · May 14, 2018 6:35 pm

300mm is the maximum unsupported length for CS overhangs.
Your bench is 80mm thick so it's quite possible that the reinforcement is built into the benchtops. That is the standard way to do it.
Just ask the question of the stonemason. They have to warrant that they are building to the suppliers standards so I'd assume that the top has the internal supports as required.
300mm overhang is adequate but 400 is much nicer and is more pleasant to sit at.

CuttingEdgeKitchens · May 15, 2018 7:09 am

300mm is the maximum overhang that CaesarStone and most other companys will warranty. Anything over that and you risk it snapping.

It may have internal supports but it probably doesn't.

I would ask them to re-install it to the manufacturers specifications!