maximum span for poured in place concrete counter

[CoastalPizza]

I'm planning to add a poured in place concrete counter adjacent to my oven. This will be supported at the back and sides on a cored block base. The depth of the counter will be about 30" and thickness will be about 3" (or more if needed). If the width of counter is about 8', how many intermediate CMU supports am I going to need along the front (unsupported) edge?

[Gulf]

You won't need any vertical supports across the front, if you design it correctly. I will elaborate when I get back to my desktop.

[Gulf]

CP,

I'm not an engineer but, I will give you my advice based on my experience

The unsupported distance of the front is approx. 80". One 8" vertical support dead center will leave two 36" spans. That is well within the limits of a properly reinforced 3.5" concrete slab.

Concrete counters aren't usually that thick. For a 30" depth, 2" is about the norm. Using standard kitchen measurnments, you have about 8" under the counter to install some horizontal support. Forming an 8"X8" "trough" underneath for a reinforced monolithic beam will give you all the support that you need to span the entire distance.

[rodeair]

I agree a 3 inch thick slab is a bit of overkill for counters. I am using Z counterform liquicrete. Basically its a 1/2 inch cement board bonded to the support followed by a mesh system. The finished thickness is 1 3/4 to 2 inches, lot less weight. Liquicrete is an additive added to sand mix. I used it for column tops and will be using it for countertops as well. Not the cheapest way, but very easy to use. Same support as Gulf suggested will give a nice slab.

[LeeBird]

I agree with Joe. You can span the whole distance. You can form a monolithic beam as Joe recommended or even a monolithic mid-span corbel could be fun. Typical counters are 2”, but this isn’t typical it’s going to require properly placed rebar. I wouldn’t go thinner than 3”, but I like my crete thick. My build has a pretty good cantilever, it’s 5” thick.

[UtahBeehiver]

Leebird is a professional concrete guy, he does it for a living so he knows his stuff.

[CoastalPizza]

Thanks Gulf, rodeair, and LeeBird - looks like I'll add in a beam, keep it at 3" and include rebar along the full run - thanks all!