Sidewalk grinding vs. saw cutting: what each leaves behind

The short answer

Grinding and horizontal saw cutting do the same job. Each takes concrete off the high side of a raised joint until the step is gone. Nothing is added, and no slab is moved.

They differ in the tool and in the surface they leave. The Federal Highway Administration's maintenance guide for sidewalks and paths, published in 2013, puts it this way: a horizontal cut leaves a very smooth surface with the stones in the concrete cut through and exposed, while grinding leaves a much rougher texture that shows the pattern of the machine. The guide calls the two "similar treatments" and expects horizontal cutting, the newer of the two, to succeed as often as grinding does.

So the choice between them is mostly a choice about the finished surface. Whether either one suits your walkway is a separate question, and the three-method comparison covers that.

Two different jobs are called saw cutting

A bid that says "saw cut" can mean either of two things, and they are not alike.

• Horizontal saw cutting is the subject of this page. The blade runs level with the walkway and slices the raised lip off. The grinding page on this site also uses the word shaving for it.
• Vertical saw cutting goes down into the slab. New concrete gets joints sawed into it so that it cracks in a straight line, where the builder wants the crack. The American Concrete Institute defines a sawed joint as one cut in hardened concrete, generally not to the full depth. The replacement page on this site describes a second vertical cut: the boundary sawed around a section before it is removed.

If a line in a bid just says "saw cutting," ask which one it is. The first removes a step. The second is a step in removing the panel.

How each one removes the concrete

The guide describes the technique in one sentence: the crew grinds the lip of the heaved section down, or uses a specially designed concrete saw to cut level with the grade of the sidewalk. Grinding is used on asphalt as well as concrete. Horizontal cutting is used almost only on concrete.

Either way, concrete leaves the slab and does not come back. The guide notes that the stones in the concrete are exposed and that the slab is thinner afterward, and it says the sidewalk still keeps its integrity. It also warns against grinding a slab past its minimum recommended thickness. The grinding section gives no figure for that. In its chapter on construction, the guide reports a recommended minimum of 4 inches for a concrete sidewalk slab, notes that sidewalks in warm climates without heavy vehicles may be as thin as 3.5 inches, and says thickness should reflect loading and soil. Those are thicknesses for building a sidewalk. The guide does not say how much can come off an existing one, so ask the contractor how thick your slab is at the joint and how much will be left.

What each one leaves behind

Texture. This is the real difference. A ground joint is rough and shows the machine's pattern. A saw-cut joint is smooth, and you can see the cut faces of the stones. Either way the stones are exposed, so the repaired band does not look like the surface around it.

Slip resistance. No source opened for this page rates one finish against the other for grip. Ask how a smooth cut face is finished, and look at a completed joint before you agree to many of them.

Slope. The guide gives a useful test. When a panel has lifted evenly across its width, a straight cut removes the step and leaves the cross slope as it was. When the panel has moved unevenly, grinding or cutting still removes the step, and the guide says it will likely leave a warped surface. It adds that the work can leave a panel or two with a cross slope above two percent, and it recommends keeping the ground panel at two percent or less. Cross slope is the tilt across the width of the path.

Dust and noise. Both machines cut concrete, and cutting concrete makes dust. A National Institute for Occupational Safety and Health study of handheld concrete grinders found the dust hazardous, and found that a shroud connected to a vacuum cut the operator's exposure by at least 90 percent in every combination tested. That study looked at grinders on walls and columns, not at sidewalk machines. It is the reason to ask any contractor how dust is collected near an entrance, a patio or parked cars.

How large a step each can take

The guide rates grinding and horizontal cutting together. It calls them most suitable as a permanent repair where a sidewalk has displaced by a quarter inch to a half inch, and as a temporary repair between a half inch and one inch.

Those are the guide's ratings, written in 2013 for agencies that maintain public sidewalks. They are not a limit for your walkway, and this page does not turn a measurement into a pass or a fail. A larger step means a longer taper and more concrete removed, and at some point the answer is lifting the low panel or replacing the damaged one.

What neither one fixes

The guide is direct about the limit. With grinding, horizontal cutting and slab lifting alike, "the underlying problems associated with these fixes may continue to be an issue." If a root is still growing under the panel, or the soil is still moving, the step can come back. Neither method raises a settled panel, and neither repairs a cracked one.

The guide is of two minds about how long the result lasts. It lists grinding and horizontal cutting among techniques that "will last one to five years." It also says many communities have success with grinding as a longer term solution, and that repairs done expertly can be considered permanent. Its caution, quoted above, is the one that decides which: the underlying problem may continue.

Choosing between them

Ask each contractor which of the two methods they use, then compare the bids on the result:

• Ask for a photograph of a finished joint on a job like yours, or look at one in person.
• Ask how far back from the joint the taper will run, and what slope it will have.
• Ask whether the panel has lifted evenly, and what the surface will look like if it has not.
• Ask how dust or slurry is collected, and what is protected nearby.
• Ask what happens to the price and the plan if a joint turns out to be too high to remove.

Next steps

Walk the property with the walkway inspection checklist so every raised joint has a label and a measurement. Read the grinding page for the conditions that suit this kind of repair, and the lifting methods guide if some panels have sunk instead. When there are many locations, start with assessment planning. Then ask about your project.