Cutting Concrete with Mesh Will it Weaken It?

Quick Column Summary:

• Installing car lift
• Need to cut into concrete
• Is mesh enforced concrete enough
• Strong concrete with steel bars needed

A reader, who is a shade-tree mechanic, is trying to install a professional car lift in his garage. Let him tell you:

"I saw a video that you posted on YouTube about the importance of steel wire mesh in concrete and so I decided to contact you for more information. My home garage concrete slab is about 4" inches in thickness and it has 6x6 steel wire mesh.

I am trying to install a 2-post car lift and the requirement is that the concrete be at least 4.25" inches in thickness, 3,000+ compression and reinforced with steel bars. I plan on cutting into the existing concrete (approx 24"x24"x24"x24") so that I can make it deeper. I would like to go about 8 inches total.

This would most likely mean that I would cut into the existing wire mesh. My question is, if I were to cut into the wire mesh, would the cut cause the other surrounding concrete to become weak? I would also like to know if you thick 8” inches would be sufficient and if I should put anything else into the 8” pit besides pouring concrete to make it stronger? Please see the attached photo of one of the post. Thanks in advance!!"

Here's the lift base.

Here's my answer to the reader:

Cutting the slab will not weaken the adjacent concrete. I'd do a saw cut through the 4-inch slab. It's not going to be easy to remove the concrete because of the mesh.

Two things: I assume you have the height in your garage to support a lift? You don't want the car crashing through the garage ceiling or up into the roof structure.

Second, I'd pour the pad at least 10-inches thick. I'd put 1/2-inch steel bars in the middle of the new concrete. Place them on 1-foot centers both ways. I'd also consider making this new pad at least 30 x 30 inches.

Quikrete has a high-strength concrete mix in a bag that's ideal for this job. You want concrete that has a PSI of 4,500 or greater. READ all of my concrete installation columns to ensure you don't goof this up!