Hopefully I'm not too late to offer some advice on your concrete and maybe some others can learn some good "stuff" about concrete. No matter where you pour a slab of concrete on the earth, gravity will start to pull down the aggregate in the matrix of the slab and pores or bleed channels form. That is the path the free-water (bleed) uses to come to the surface, weeks, months and years after. I'm talking about unenhanced concrete. 9' x9' x 4" thick is one cubic yard of concrete; most Batch Plants will use 32 gls of water / cyd when mixing and transporting your concrete. That 4" slab only needs about 15 gls to make the concrete hard, which leaves 17 gls of free-water to cause all kinds of problems with your slab. Here comes my sales-pitch! If you are considering in the future an epoxy floor or just an extremely densified floor, use a concrete admixture called Vapor Lock by Specialty Products Group. Vapor Lock Enhanced Concrete, VLEC, uses that 17 gls to make additional CSH gel. Calcium Silicate Hydrate is what makes concrete stronger. VLEC will virtually double your psi strength, waterproof and vaporproof, it's a shrinkage reducer and a corrosion inhibitor. I HAVE THE DRYEST GARAGE IN MICHIGAN. Depending on your location, VLEC could add $40-$50/ cyd to your cost. Your slab @ 4" thick is about 29+ cyd so for about $1200 you will have zero moisture from your slab, zero slab sweat...and always remember, Mother Nature wins 100% of the time so your concrete might still crack. I've presented to thousands of Architects & Engineers and one question is "do I need the vapor barrier under the slab?" My garage slab doesn't have one but that is the least expensive part of your garage so when the concrete cracks, the Engineers want it there. VLEC stops all transmission of moisture and vapor thru concrete in any direction. Hope this helps and enjoy the build
