actually brigitte2530 30mm you can have a 15" overhang you can have upto 16" with no additional support.

As per all the quartz manufacturers fabrication guides.

I am a fabricator. Quartz is unlikely to break with a 13 or 15" overhang. However, while far less common than natural stone a quartz slab can also have an inherent weakness that is not apparent. Once in a while a slab will crack while it's being sawn or CNC'd due to a material flaw.

A large unsupported overhang represents a considerable hazard in the event of a material failure or a break due to abuse which send a piece of material weighing 17.5 lbs per sq. ft. crashing to the floor. I would still recommend some type of support.

I had a customer that had a large quartz overhang (not installed by me) break when someone dropped a stack of two 24 packs of soda on the overhang. Drop height was only several inches.

oldryder do agree , but to break 30mm on an overhang with a cantilever you would have to have a party of the near the edge of the overhang. But it would not break with 48 can of soda, there was another issue there or the customer as you know say "it just happened"

Our concern would be not the overhang but the cabinets where bolted to the ground so they did not topple over and kill someone.

IMO any overhang needs support and the invisible steel ones are awesome and of course those cabinets have to be anchored to the floor.

What are the invisible steel braces for quartz overhang? I am deciding whether to settle for a 12 inch overhang or go for the 16 inches I have now (with laminate countertop.) Thanks for any advice.

Linda:

If by "quartz" you're referring to engineered stone and not quartzite, you can cantilever 3cm up to 15" without additional support according to the manufacturers, however, based on my experience, I wouldn't cantilever that much with a span of more than 5' or so without additional support because the estone will sag.

This is an older thread and is primarily focused on natural stone, not man-made quartz, but it might give you some useful information, including the Counter Balance system.

https://www.houzz.com/discussions/2543583/granite-fabrication-questions-what-do-you-think

https://www.houzz.com/discussions/2516280/kevin-remember-the-6-10-rule

https://www.counterbalanceshop.com/counterbalanceshop.html