Can a 4-Inch Slab Hold a Car Lift?

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Featured image with the headline Can a 4-Inch Slab Hold a Car Lift, beside two tall plain grey posts joined by a thin beige bar on a pale slab, the right post cut off by the edge

Can a 4 inch slab hold a car lift? The answer changes with the lift on the box. A true 4 inches sits right on the line for some makers and just under it for others.

Quick Answer

It depends on the lift. A true 4 in slab is at the stated floor in the Atlas 9KOH and Challenger DX77 manuals. It is below BendPak’s 4.25 in rows and Rotary’s 4-1/4 in anchor table. Rotary’s FAQ names five inches as a general rule. Read your own lift’s manual and measure the slab.

Does a 4-Inch Slab Meet Each Lift Maker’s Minimum?

Only for some makers. Atlas states a 4 in minimum thickness for its 9KOH two-post lift (9,000 lb). Challenger states 4 inches minimum depth for its DX77 dual scissor lift (7,700 lb).

BendPak’s table lists 4.25 in for the M7K, GP-7, XPR-9 and 10AP two-post series. Rotary’s anchor table lists 4-1/4 in for its 500, 700 and 800 series two-post lifts when the Hilti Kwik Bolt III anchor is used. The gap is small, and the arithmetic is 4.25 – 4.00 = 0.25 in. BendPak prints 4.25 in as 108 mm.

Rotary’s FAQ gives a different general rule: “a five-inch depth of 3000PSI concrete is essential”. The FAQ adds that special requirements may exist and that you should confirm with your distributor. Rotary’s two documents differ, so a Rotary owner should ask the distributor which applies.

Bigger BendPak lifts ask for more. Its table lists 6 in for the XPR-12 and 12AP series and 8 in for the XPR-15/18 and 16AP/20AP series. The table prints no lift capacities, so this article gives none for BendPak. No document read says a thinner slab is acceptable.

Stated minimum slab thickness by maker and document One-scale bar chart, 30 pixels per inch from 0 in. Atlas 9KOH 4 in. Challenger DX77 4 in. BendPak M7K, GP-7, XPR-9 and 10AP 4.25 in. Rotary 500, 700 and 800 series sheet 4-1/4 in. Rotary FAQ general rule 5 in. BendPak XPR-12 and 12AP 6 in. BendPak XPR-15/18 and 16AP/20AP 8 in. BendPak new two-post slabs 12 in. A vertical line marks a true 4 in slab. Stated minimum slab thickness, by maker and document Scale: 30 px per inch, bars start at 0 in. The line marks a true 4 in slab. a true 4 in slab Atlas 9KOH manual 4 in Challenger DX77 manual 4 in BendPak M7K, GP-7, XPR-9, 10AP (Table 1) 4.25 in Rotary 500/700/800 sheet (Kwik Bolt III anchor) 4-1/4 in Rotary FAQ, general rule 5 in BendPak XPR-12, 12AP (Table 1) 6 in BendPak XPR-15/18, 16AP/20AP (Table 1) 8 in BendPak new two-post slabs (Table 2) 12 in Each bar is one maker’s own figure from its own document. The figures are not combined.
Minimum thickness as each document states it, at one scale.

Why Measure the Slab Before You Trust the Label?

Because BendPak requires it. Its concrete-requirements document (Ver. 2 Rev. B2, Feb. 13, 2025) says an existing floor must be test drilled to find the actual thickness where the lift will stand. It also requires a core sample and test to confirm at least 3,000 psi.

The same document sets other limits on an existing slab. The concrete must have cured at least 28 days. A lift never goes over expansion or control joints, damaged or defective concrete, or hand-mixed concrete. The document says never to drill or cut into a post-tension slab.

It also bars a lift on a secondary floor level, or over a basement, without written authorization from the building architect and BendPak. It strongly recommends consulting a concrete specialist.

The slab load capacity calculator is not a lift check. It models one interior load from thickness, concrete strength, subgrade modulus, load radius and a safety factor. It has no edge, joint, anchor, multiple-load or dynamic case. Its default example (6 in, 4,000 psi, k 150) gives about 6,690 lb as a single interior load. Do not set that figure beside a lift’s load.

The BendPak document was read on a retailer-hosted copy. The Rotary and Atlas documents were read on dealer-hosted copies, and the Challenger manual on a retailer file. Each is the maker’s document, and each was accessed 2026-10-21.

How Do Strength, Cure Age and Edge Rules Differ?

They differ by maker and model, so no single set of numbers covers every lift. The table keeps each maker’s figures apart.

Stated slab rules by maker, series and document
Maker, series and document Minimum thickness Strength Cure Edge and seam rule
Atlas 9KOH two-post, manual revised 8/12/2020 4 in 3000 psi “Properly cured”, no day count 6 in from a slab edge or seam; no cracks within 36 in of the base plate; no seams within 6 in
Challenger DX77 dual scissor, installation manual 4 in, with steel reinforcement 3500 psi 28 days No anchors within 8 in of any crack, edge or expansion joint
BendPak M7K, GP-7, XPR-9, 10AP, existing slab (Table 1) 4.25 in 3,000 psi, core tested 28 days Anchors 6 in from seams, control joints or other inconsistencies
BendPak XPR-12, 12AP and XPR-15/18, 16AP/20AP, existing slab (Table 1) 6 in; 8 in 3,000 psi, core tested 28 days Same BendPak 6 in rule
BendPak two-post, new slab (Table 2) 12 in 4,000 psi 28 days Anchors 6 in from the new slab edge
Rotary 500, 700, 800 series, installation instructions 4-1/4 in 3000 psi Not stated for the slab Minimum edge distance 3-3/8 in for the Kwik Bolt III anchor

The Challenger DX77 manual also gives 6 in from any crack, edge or expansion joint in its anchoring step. An owner of that lift should read both passages. Rotary’s anchor figures apply to the anchor named in its table, not to every anchor.

Column base on a slab, with seam and crack clearances Illustrative plan view, not to scale. A square column base plate sits inside a clearance zone on a slab. A vertical seam runs along the right side and a crack runs diagonally on the left. Notes: Atlas 9KOH, no cracks within 36 in of the base plate and no seams within 6 in. Challenger DX77, no anchors within 8 in of any crack, edge or expansion joint. BendPak, anchors at least 6 in from expansion seams, control joints or other inconsistencies. Illustrative, not to scale: where the maker rules apply seam or joint crack clearance zone (illustrative) column base plate Atlas 9KOH: no cracks within 36 in of the base plate, no seams within 6 in Challenger DX77: no anchors within 8 in of any crack, edge or expansion joint BendPak: anchors at least 6 in from expansion seams, control joints or other inconsistencies
A sketch of the idea only. Distances differ by maker and are not drawn to scale.

What If the Anchors Will Not Tighten?

Rotary and Atlas both say to replace the concrete under each column base with a 4 ft x 4 ft x 6 in pad of 3000 psi minimum concrete. The pad is keyed under and flush with the top of the existing floor. Both say to let it cure before installing the lift and anchors.

This applies when the anchors will not tighten to 110 ft-lbs. Atlas says the pad typically cures in 2 to 3 weeks, and the Rotary sheet gives no time. Challenger’s DX77 manual says a pad may be poured when its conditions cannot be met, and to check with local building inspectors. Rotary says a seismic install needs your structural engineer and the manufacturer’s representative.

Here is the pad volume, as arithmetic and not an order quantity. The 4 x 4 x 6 in size is Rotary’s for its 500, 700 and 800 series and Atlas’s for the 9KOH. Do not carry it to another lift.

  1. Convert the depth. 6 in / 12 = 0.5 ft.
  2. Find one pad. 4 x 4 x 0.5 = 8 cu ft per column base.
  3. Convert to yards. 8 / 27 = 0.296, about 0.30 cu yd per column base.
  4. Count two bases. A two-post lift has two column bases, so 2 x 8 = 16 cu ft, and 16 / 27 = 0.593, about 0.59 cu yd.

The total is 0.59 rather than 0.60 because 0.296 was rounded in step three. The sum adds no waste.

What Should You Check Before the Lift Goes On?

Check the slab against your own lift’s manual, in the five steps below. The list is drawn from the maker documents read, and it is not a ranked procedure.

Five slab checks before a lift install A row of five boxes joined by arrows: measure thickness, confirm strength, check age, check edges and joints, ask the maker or an engineer. Illustrative checklist with no numbers. Checks to make, drawn from the maker documents 1. Measure thickness 2. Confirm strength 3. Check slab age 4. Check edges and joints 5. Ask maker or engineer
Five checks, each tied to a maker’s own document.
  • Thickness. BendPak requires a test drill at the install spot.
  • Strength. BendPak requires a core sample and test. Makers name 3,000 or 3500 psi, so use your lift’s figure.
  • Age. BendPak and Challenger DX77 say 28 days.
  • Edges and joints. Use the distance in your own manual.
  • Doubt. Contact the maker, the distributor or an engineer.

For general slab depth by use, read about how thick a slab should be. For what sits under a garage floor, see vapor barrier under a garage slab.

Want a single-load slab estimate?

Try the concrete slab load estimator for one interior load. It does not check a lift. More tools are in the slabs and flatwork calculators.

FAQs About Car Lift Slabs

Can a 4 inch slab hold a car lift?

It depends on the lift. Atlas 9KOH and Challenger DX77 name 4 in as a minimum, while BendPak’s 4.25 in rows and Rotary’s 4-1/4 in anchor table sit above a true 4 in slab.

What strength does a lift slab need?

It depends on the maker. BendPak for existing slabs, Rotary’s anchor table and Atlas name 3,000 psi. Challenger names 3500 psi for its DX77. BendPak asks for 4,000 psi in new slabs.

How long must the slab cure before installing a lift?

BendPak and Challenger’s DX77 manual say 28 days. Atlas says only that the slab is properly cured, with no day count. The Rotary sheet gives no slab cure age.

How far must anchors be from edges and joints?

Each maker sets its own. Atlas and BendPak say 6 in from seams, Challenger DX77 says 8 in from any crack, edge or joint, and Rotary’s sheet lists 3-3/8 in for one anchor.

What if the anchors will not tighten?

Rotary and Atlas both say to replace the concrete under each column base with a 4 ft x 4 ft x 6 in, 3000 psi minimum pad. Atlas says it typically cures in 2 to 3 weeks.

Do bigger lifts need a thicker or new slab?

BendPak lists 6 in for the XPR-12 and 12AP and 8 in for the XPR-15/18 and 16AP/20AP on existing slabs. For new two-post slabs it lists 12 in thick, 4,000 psi concrete.

Who should check an unknown slab?

BendPak requires a test drill for thickness and a core test for strength, and strongly recommends a concrete specialist. Rotary says seismic installs need a structural engineer.

Sources and Further Reading

References Used in This Article

Every figure belongs to the maker and document named beside it. Lift makers differ on slab thickness, strength and edge rules, so follow your own lift’s manual and have an unknown slab tested. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated 2026-10-21.