KevinRH

I am building a detached garage part of which has a 12 foot ceiling. I am looking at different lifts and only one of them indicates a specification of 3,000 psi rebar reinforced concrete. My floor is 3500 psi with fiberglass strands for reinforcing. my builder told me that if he had not used fiberglass he would have used welded wire mesh but not rebar. I will certainly have my pickup on the lift so there could be up to 1450 pounds on each leg. anyone have any problems with their floor cracking with a Lift?

0Fastrak

How thick is it? I know most lifts say that you need at least 6" seriously thou when i put mine in thats what they asked me and since mine was a commercial building it was at least 6" thick

rjacobs

yup, thickness counts...thats what she said.

You can always get the concrete where the legs are going to go cut out and basically piered deeper/thicker to get what you need.

HOXXOH

I assume it's a 4-post lift and that's why you don't find concrete specs. A 3500psi slab is overkill for a 4-poster, but 3000 @ 4" thick is the minimum for a 2-post lift.

My builder screwed up and now I have to demo out a portion and will repour 4000psi 6" thick for my 10K# 2-post lift.

See this and post #4.
https://www.corvetteforum.com/forums...one-built.html

unixcorn

Before I bought my four post lift, I reconciled this in my mind by thinking about the car in the garage not on the lift.

Think of the small contact patch where each of the four tires sit on the concrete. Now think about the contact patches of the lift. Yes, the lift adds some additional weight but the contact patch for each leg is bigger than the tires so the load is spread a bit.

So, if the garage floor holds your car without cracking, it should certainly hold your car on the lift.

KyJim

What is your slab thickness and what is the base below the slab ? (crushed stone, sand, etc?)
What is the lift base plate size and what is the weight of the lift.
If you are lifting a truck you are adding most likely 6000 lbs. plus additional dead load.
Compression wise you are fine, but the fiberglass actually hurts you for this application.

Fiberglass is normally used to control cracking from shrinkage do to water evaporation as the concrete cures. Some fibers are used to increase the abrasion and shatter resistance in concrete.
Fiber reinforcing does little to increase the flexural strength so the moment-resisting reinforcement that is provided by wire mesh or re-bar is not there.
Send what you have and I will give you info as to what you may or may not need to do. At the worst case you may need to cut out a section of slab at each post and pour a reinforced pier. That is the safe solution.

The issue with concrete going to residential projects is you don't know what the mix design actually is as it's never tested and many times is over temperature.

WW7

A 2 post lift requires 6" reinforced concrete. A 4 post lift is fine on standard 4" concrete, which is what most homes have in the garage...WW

zrracer

The floor will support 3500 pounds per sq inch (psi).
No way u could figure out how to do that.
U r only going to spread out 1450 pounds over the entire base of the lift.
If your builder did the 3500 floor with out asking or charging more he is a keeper!
Robin

jjbravo1

6" 3500 lb fiberglass.
14 years, all manner of cars / trucks.
Good packed gravel bed underneath.
No cracks except for the at the control joints.
Make sure to re-inspect your lift bolt anchors after a few months and re-torque.

Seadawg

The bigger question to ask is how well was the area prepped BEFORE the concrete pour. Meaning, it has to be tamped/packed properly, set up so that no water/moisture from your house draining can cause settling later, etc.

In over 40 years, I've never seen a home garage concrete pad fail or structurally crack - that did not have a settling issue of some type as the root cause of the problem.

So, to the OP, if you drill your anchor holes all the way thru the concrete, which will verify (at least at those points) your pad thickness. And, if you stick a metal coat hanger in the holes, and they are solid there, you don't have a problem from settling issues.

IF you find that there are voids or soft soil locations, you need to find out if it is settling issues, or moisture/water causing the voids. If settling, it can be remedied by getting some of the pourable fillers (to fill those voids).

If it is water related, you have to fix your house roof drain issue, or figure where else the water is coming from, that is causing the wash out of the soil under the concrete.

But I always drill completely thru a slab when installing something like this, to see how it looks below it

njk4o5

4" 3000PSI is minimum on 99% of 2 post lifts. no idea on 4 post but I can only assume its less. Keep in mind most 4" slabs are not 4" in every single location

cmonkey713

Six inches with 4000 LB concrete should do it very nicely.

Maineah

You could add larger plate steel under the base plates of the lift that would distribute the load better. You should use fairly thick steel that would not deflect, maybe 1/2".
Jeff

1972bluelt1

I have 5" of 4000# concrete and a 9000# asymmetrical Bendpak 2 post lift. 15 years and no problems.