Hearth pour too thin?

[damiano]

I didn't want to brave the hearth myself so instead had a contractor pour it. He was a masonry guy specifically, not a concrete guy, but assured me he has done plenty of slabs.

However, the forms came off today and it looks like it's closer to about 3.3" thick than 3.5". Not sure if it was just carelessness on his part or what. My understanding is that 3.5" is the accepted minimum so now I'm paranoid that it will be a problem.

Will I still be alright? My feeling is that a lot of build recommendations are a bit overkill to be extra safe but obviously this is an important one. For reference, I have a standard CMU base that is about 65x63, so the maximum unsupported span of the hearth is about 49". My plan is for a casa80 or 90 with minimal finish materials (e.g., only a stucco dome).

If I did want to reinforce it somehow (without having it torn off and starting over), what are my options? E.g., would it be at all helpful to add another 2" or larger slab (such a as a vermiculite slab) on top of it?

[rsandler]

Assuming the contractor added the recommended amount of rebar reinforcement, I think it's probably fine. The CMU stand recommended by FB is over-engineered anyway; losing .2" from the hearth thickness isn't going to make a noticeable difference if the reinforcement is there. I am not an engineer and haven't done a calculation of the weight bearing capacity,

Adding a vermicrete slab on top isn't going to do anything structural (obviously it would add insulation, which is good).

[Olivia Wilson]

I’m new here and just starting to plan my build, so it’s really helpful to read questions like yours and the experienced replies. I was also worried about “what if it’s a little thinner than spec,” so it’s good to hear that .2" isn’t likely a deal breaker if the rebar is done right. Looking forward to following your progress and learning more!