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Lightweight Concrete Garage Slab

Lightweight Concrete Garage Slab

(OP)
Hello all,

Forgive me for not doing enough research before exploring solutions from all of you, but I could use some help and I thought my question may be something up someone's wheelhouse. I need a lightweight concrete slab mixture and reinforcement for a garage supporting vehicle loading. The thickness of the slab will be anywhere between 1-3/8" to 3-3/4" for sloping and general leveling issues, sitting on a slip sheet of visqueen over OSB subflooring. Anyone have any design recommendation to prevent cracking in the slab?

Thanks all,
R

RE: Lightweight Concrete Garage Slab

The slab will crack no matter what you do. You just have to define how much you can tolerate between the shrinkage and deflection cracking. I would use a minimum of 3" though and go up from there for any drainage.

Mike McCann, PE, SE (WA)


RE: Lightweight Concrete Garage Slab

(OP)
Thanks for the words of advice. I'll have to disclaim that there's no real solution I'd be comfortable with and to put in more frequent joints.

How would you reinforce a 3" lightweight concrete slab? Any preference on the f'c or mix suggestions?

RE: Lightweight Concrete Garage Slab

Why are you placing a concrete slab over wood framing to support vehicles? Unless you have carefully designed the framing and subfloor, you are guaranteed to have cracking problems and structural issues. I hope the space below is not occupied. Further, 3 inches of concrete would be bare minimum as Mike noted.

RE: Lightweight Concrete Garage Slab

(OP)
Out of curiosity, how would you address having a garage over habitable space, in the context where all applicable structural elements are made of wood? What cover would you place over the plywood diaphragm?

RE: Lightweight Concrete Garage Slab

My first choice would be a compressed fibre cement sheet underlayment for a trafficable membrane.

RE: Lightweight Concrete Garage Slab

(OP)
@hokie66 - I haven't heard of that before, thank you. I'll check it out.

RE: Lightweight Concrete Garage Slab

It is a common solution in Australia, but I don't know about the US. James Hardie would be the most likely supplier of compressed fibre cement, I think.

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