Max Jax Floor Requirement

I'm thinking of getting a Max Jax but unsure whether my driveway is suitable to mount it. The instructions say that 4" of 3000psi concrete is required - I can measure the depth easily enough but don't know of an easy way to check the strength of it.

Any idea what the compressive strength of a typical 1950s concrete driveway is? Maybe just get one and keep a close eye for any cracking where it mounts?

Sorry.  I posted something then realized I hadn’t understood your question.

I gots nada.

Your life ain't worth not being sure what your lift is sitting on.

If unsure, I would recommend cutting out an appropriate size square at the location of each post, dig down a bit, and pour a sizable block for the post to sit on with the necessary strength rating concrete. Also, drilling into the existing slab edges and epoxying rebar to link the new blocks to the slab would help tremendously. Concrete cutting saws can be rented at your local tool yard.

I've got a garage floor that JUST meets the MaxJax spec, and I'm a little nervous with my lift. I'm going to do what I describe above in the next few years. In the meantime, I only lift stuff up to about 3/4 the MaxJax capability.

Good call, Cadman.  Concrete failure tends to be sudden and with little advance warning.

If it was me working under there, I'd really like to see better than 3000# concrete, and for added-in squares - or one big rectangle covering the floor area for both posts - it wouldn't hurt to go a bit thicker than 4" either.  For inserted squares/whatever, you're going to want to make sure that they're big enough for the base/subgrade underneath to provide sufficient resistance against some amount of overturning (I'm not going to guess how much here, and I'm not willing to rely entirely on edge contact with the 3000# balance of the floor for much help either).

In a previous life I would occasionally run calculations for anchor-bolted plates used to support fairly large pipes.

Norm

My garage floor wasn’t thick enough to meet minimum specs so I had a 6” thick pad poured.  It is 12’ x 2’.  Crew came in and cut the existing floor out, hand dug and leveled grade, set up rebar and poured and leveled pad.  I let it cure for a while before drilling and setting epoxy anchors.  

Mine is driveway mounted when in use. No clue on the PSI rating beyond the 15000 pound SanFord not cracking it. Max weight I've lifted is 4500 pounds. I have had it for a couple of years now without issues and no signs of cracking. 

Thanks, I think I should probably get a new pad cut in.