How thick a slab ?

[Choppedsled]

Hello, I 'm having the floor done in my new shop as part of the build. My question is I plan to add a lift in the near future, so how thick a slab should I have etc. I haven't settled on a brand or model of lift yet so I need to be sure what ever I buy will work with my slab. I do know I won't be lifting much more than an average suv at the very most. Thanks in advance !

 

[beltfeed]

Two post or four post lift? Two posts need thicker concrete then four posts. Most four posts spec 4" min. Also if you know where you are going to place the lift you can always dig out a pad section in the ground 4"-6" deep. That would make the area where the lift would go 8"-10" thick and the rest of the floor 4".

 

[Choppedsled]

I'm hoping for a two post lift. The floor is spec'd as fiber reinforced 4", and they have agreed to pour it deeper where I need it. So I guess I should narrow down the location for a two post and do a deeper pour in that location. I know what bay it will be located in but not the width or deminsions of the lift as I don't have one picked out yet. Advice?

 

[dawg]

when I poured my floor I put 12 " of concrete with rebar in the spot where the lift would go.
the mfg (bendpak) said 6" minimum of reinforced concrete for the 2 post lift.
(also dependant on the type of reinforced concrete)
alway better to err on the thick side

 

[z28toz06]

This is what Bendpak sent me for their 10AC lift. 2 Post asymettrical.
Lift Concrete Requirements


Before installing your new lift, check the following.
1. LIFT LOCATION: Always use architects plans when available. Check layout dimension against floor plan requirements making sure that adequate space is available.

2. OVERHEAD OBSTRUCTIONS: The area where the lift will be located should be free of overhead obstructions such as heaters, building supports, electrical lines etc.

3. DEFECTIVE CONCRETE: Visually inspect the site where the lift is to be installed and check for cracked or defective concrete.
Specifications of concrete must be adhered to. Failure to do so could cause lift failure resulting in personal injury or death.
A level floor is suggested for proper installation and level lifting. Small differences in floor slopes may be compensated for by proper shimming. If a floor is of questionable slope, consider a survey of the site and/or the possibility of pouring a new level concrete slab.
• DO NOT install lift on any asphalt surface or any surface other than concrete.
• DO NOT install lift on expansion seams or on cracked or defective concrete.
• DO NOT install lift on a second / elevated floor without first consulting building architect.
• DO NOT install lift outdoors unless special consideration has been made to protect the power unit from inclement weather conditions.
CONCRETE SPECIFICATIONS
LIFT MODEL CONCRETE REQUIREMENT
7,000 Pound Two Post Models 4 ” Min. Thickness
9,000 Pound Two Post Models 4 ” Min. Thickness
10,000 Pound Two Post Models 4” Min. Thickness
12,000 Pound Two Post Models 6” Min. Thickness
15,000 Pound Two Post Models 6” Min. Thickness
18,000 Pound Two Post Models 6” Min. Thickness
7,000 Pound Four Post Models 4 ” Min. Thickness
12,000 Pound Four Post Models 4 ” Min. Thickness
18,000 Pound Four Post Models 4” Min. Thickness
27,000 Pound Four Post Models 4” Min. Thickness
35,000 Pound Four Post Models 4” Min. Thickness
40,000 Pound Four Post Models 4” Min. Thickness

NOTE: All models MUST be installed on 3000 PSI concrete only conforming to the minimum requirements shown above. New concrete must be adequately cured by at least 28 days minimum.

 

[Choppedsled]

Thanks, for taking the time to answer this post. All of the information is very helpfull! I'll get with my concrete guy and see if we can do a bit of overkill to be on the safe side!

 

[dxdexter]

One point often overlooked is the compaction of the backfill materials. Regardless if you use the proper thickness of concrete, if the fills beneath the slab are not compact then " punch through" or cracking around the units legs will result, as the slab acts as a bridge (flexural loading) over soft spots. This is especially apparent with point loading as you have in this case.

It would be advisable to have the contractor extend any rebar from the thickened area up into the main slab so as to minimize cracking occurring where the slab narrows. Cracking will occur in the path of least resistance and that is where the thickened pad meets the narrower slab.

I would recommend a minimum compressive strength of 4000psi (28Mpa) for any garage slab and preferably 4700psi (32Mpa) for durability . If exposed to freeze thaw and/or road salts then air entrainment (AEA) should be specified (5% to 8%) unless you are using surface hardeners (dry shake) then check with hardener manufacturer for compatibility.

 

[Choppedsled]

Very good point. I'm considering pouring a 12' X 12' section 8" thick with rebar in the middle of the bay it's going in. The area it's going over should be very compacted as it's mostly hard as a rock. Question: How much rebar, and spacing, layout etc ?

 

[dxdexter]

Very good point. I'm considering pouring a 12' X 12' section 8" thick with rebar in the middle of the bay it's going in. The area it's going over should be very compacted as it's mostly hard as a rock. Question: How much rebar, and spacing, layout etc ?

Generally speaking a small slab-on-grade does not require any rebar or welded wire fabric (wire-mesh) for structural soundness, but do so for crack control. I would suggest if you have a well compacted base then place a 6"x6" or 4"x4" WWF at the center of the slab thickness , but 2" below surface is suggested. If you are only reinforcing the area in which the lift sits then you could extend the WWF out to the limits of the saw cuts and discontinue it there. The slab should crack in the joints.

If you intend not to saw cut then place the WWF over the entire area. The price is a small fraction of the entire slab.

Be careful of the claims made for fiber-mesh concrete. They are great at controlling cracks , but are not always 100% effective.

 

[ron in sc]

The requirements for a lift are pretty minimal. Deciding things like thickness, strength, welded wire, fiber, rebar and the like have more to do with durability, minimizing crack and settling. As was stated above proper site preparation is key.

The concrete I ordered was to be minumun 4000 psi. The concrete ended up being 6.5" to 7.5" thick. The 7 day test showed 3860 psi and the 28 day test showed 4640 psi.