| To tack on to Marshalls comment about floor strength, I’ve been meaning to throw in the following about moving a lift with a car on it.
If you have a lift on casters with a car on it (I.e. John Grady’s point of having an inop car), all the weight which would otherwise be spread out over a larger surface area of footprint from the posts is now on the very much reduced surface area of only where the caster wheels contact the floor. This is a lot of force on a small area. It’s spread out over the multiple wheels but the weight on each wheel is pushing down on small “line” where the curved wheels contact the floor. So is 4” of concrete enough? Not sure what the magic number is but something to consider. Sent from my iPhone On Dec 2, 2023, at 17:35, Nick Taylor <nicksgaragesd@xxxxxxxxx> wrote:
Here is an album on my workshop. If you go to the bottom you'll see the slab work. I have them make it thicker in the area where the two-post lift was going. About 6 inches thick there. I'd have to look up in my records for the strength. I had the floor epoxied and haven't had any cracks. I've had problems with the outside concrete, including having to have a big section replaced.
I put in my new concrete floor and 2-post lift 2 years ago after much research concerning the concrete. My lift brand called for 5.5" of reinforced concrete with 4000# test compression.
What I found out in several conversations with flatwork companies, and also through independent online queries, is that today's recommendations regarding reinforcement and thickness have changed considerably from the old days. First, a number of years ago they came out with microfiber reinforcement. The recommendation then was to put a certain amount of microfiber, leave out the wire mesh, but still use rebar. Then a few years ago they came out with macrofiber reinforcement, and it was a real game changer. Testing showed that macrofiber inclusion in the concrete mix eliminated the need in most cases for either wire mesh or rebar.
The problem with wire mesh had been that even though it is intended to be held up in the pour on "chairs", the truth is that a lot of it would get mashed down to the bottom by the guys laying the pour instead of ending up in the upper third of the thickness where it might do some good. Rebar also has the problem of rusting and busting up the concrete over time if it's used in wet locations. With macrofiber those problems are history as the reinforcement is consistent throughout the mix from bottom to top.
Testing has also shown that macrofiber reinforced concrete can even be laid thinner than wire-mesh and rebarred concrete and yet achieve equal performance characteristics. My recollection is that the thickness reduction can be about 20%.
The bottom line is we put down 7500 square feet at 5" thickness using only macrofiber reinforcement right in the mix. We also cut control slots. This was two years ago and I have yet to see even a single hairline crack anywhere. It troweled out to a fairly slick surface and we hit it with a coat of densifier too to eliminate dusting of the surface.
This new development is fantastic and the flatwork companies are all using it.
Keith Boonstra -
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