Thanks Dargo. When you say no less than 6" thick concrete, should I consider another truckload of concrete in the floor to get around 7-8 inches thick? I only want to do it once and want it right.
Well, it's all too easy to spend someone else's money, but if you read my post with the picture of the pumper truck in the barn you can read that I went 10" in that barn. I park my dumptruck in there quite frequently with about 23,000 to 24,000 pounds on a trailer attached to it. Also, you can't go back and add an inch when you're finished. Most concrete companies do exactly what the previous poster said; use 2X4 lumber for a "4 inch floor" actually leaving you only get 3 1/2". The same goes for most concrete companies who do "6 inch floors"; that are only really 5 1/2" thick.
I used a large commercial concrete contractor and my 2000 yard total job (barn and driveway) was just a small job for them. They have actual steel and aluminum forms that are a true 4", 6", 8" etc. They don't use lumber for forms. You don't want a company to tell you that you're getting a 6" floor, only use 3500psi concrete and then have high spots under the floor leaving you with only 3" or so in spots, especially if you're going to put in a 2 post lift. I have 4 lifts; two 2 post lifts and 2 four post lifts. I'd strongly prefer to not play "catch" with a nearly 9000 pound dually falling on me. Or, more likely, have the floor crack, weaken, and fall when you are later lifting something.
Again, I am
not a professional concrete guy. I'm just a guy who has spent a load on concrete and strongly prefers it to last. You don't need your barn floor poured to AASHTO T 22 specs (only for my bridge), but when you spend a considerable amount of money for a concrete floor, you do want it to last. You may want to ask your contractor what their ASTM/ACI compliant numbers are. I didn't do my research and shopped by mainly price alone on my first barn and my FF number for the floor is only in the mid 30's. In the barn pictured being poured, that company provided me with certified proof that they average between 60 and 70 on almost all jobs and can do an even better job for more money. They provided me with a binder of ASTM E1155 certified 60+ floors. Basically that means that per each 10' I should have less than an 1/8" of deviation in the levelness of the floor.
You really want a floor to be at least well into the 30's if you are going to have any drains in it and will have any water on the floor or you'll have puddles to deal with. Most residential companies can't do FF numbers over 40 or 50, but that is plenty fine. I figured I was already spending a lot of money so I spent the bit extra for the better grade finish, higher psi concrete (my 2nd barn and driveway are 4500) and firmly believe in the heavier wire matting (basically 1/4" rebar formed into 10'X15' sections). Sorry if I got carried away with explaining, but to me I spent a lot of money and wanted to do my research and get a good company. Good luck with your floor!
