Last Updated on October 20, 2026 by Umar Farooq
A walk behind concrete saw (also called a flat saw or floor saw) is a wheeled saw that runs a 14- to 20-inch diamond blade through a concrete or asphalt slab in a straight, controlled line. For work before pavers go in, such as cutting back a patio slab, squaring off a driveway apron or cutting out a section to replace, rent a 14-inch gas saw and cut it wet: EDCO's KL-14 reaches 4 3/4 inches deep, which covers a typical 4-inch residential slab. Step up to an 18- or 20-inch saw only for thicker slabs, and use a handheld cut-off saw instead when the cuts are short.
That is the answer for most homeowners. The rest of this guide covers how to size the saw and blade, what to ask at the rental counter, and how to run the cut without the two mistakes that end walk-behind jobs early: burying the blade and running a gas engine where the exhaust can't leave.
When a paver job needs a walk-behind saw
A handheld cut-off saw and a walk-behind saw both cut concrete with a diamond blade. The difference is control. A handheld saw is steered by your arms, so a long cut wanders and the depth varies. A walk-behind rides on wheels with a depth wheel, a guide pointer and its own weight holding the blade in the cut, so a 30-foot line stays straight and even.
On a paver project, that matters in a few specific jobs:
- Cutting back an existing patio slab so the rest can be broken out and replaced with pavers.
- Squaring a driveway apron or edge before a paver extension or border. Our driveway paver extension guide covers what happens at that joint once it is cut.
- Cutting out a strip for a trench drain or a utility line crossing a slab.
- Making a clean, straight edge where pavers will meet concrete, so the joint looks deliberate rather than broken.
Where a handheld saw is enough:
- a few short cuts, a corner notch or a cut along a wall;
- cutting pavers themselves, which is covered in our cut off saw guide;
- anywhere the walk-behind can't physically reach.
My rule of thumb: once any single straight cut is longer than about 10 feet, or the slab is thicker than a handheld blade reaches, rent the walk-behind. Below that, the handheld is faster to set up than a machine you have to unload.
Blade size sets the cutting depth
Only part of a blade's diameter becomes depth, because the arbor, flange and guard sit above the slab. The usable figures come from Rntr's concrete saw size guide and EDCO's spec pages:
| Blade | Approximate max depth | Source |
|---|---|---|
| 12 in | about 4 in | Rntr |
| 14 in | 4 1/2 to 5 in (EDCO KL-14: 4 3/4 in) | Rntr, EDCO |
| 16 in | 5 1/2 to 6 in | Rntr |
| 18 in | 6 1/2 to 7 in (EDCO KL-18: 6 3/4 in) | Rntr, EDCO |
| 20 in | 7 to 8 in (EDCO DS-20: 7 3/4 in) | Rntr, EDCO |
Measure your slab before you choose. Break a small chunk off an exposed edge, or look where the slab meets soil at a step or the lawn, and measure the actual thickness. A slab poured as "4 inches" is often thicker in spots where the ground was low. Add a margin; you want a saw that reaches past the bottom, not one that stops a quarter inch short.
Do you need to cut all the way through? Not always. If you are removing the slab on one side of the line, cutting partway down and breaking the rest out with a sledge or breaker works, and the break usually follows the cut. If the slab on the other side stays in place and must look clean, cut full depth so the break can't wander into the part you keep.
Diamond blades for a flat saw
Walk-behind saws take larger blades than handheld saws, with 14 to 36 inch sizes on a standard 1-inch arbor according to Concrete Cutting Pro's buying guide. For homeowner work, three details matter:
- Match the blade to the material. Cured concrete, green (freshly poured) concrete and asphalt each have their own blade specs. An asphalt blade used on hard cured concrete glazes; a hard-concrete blade on asphalt wears fast.
- Wet or dry rating. Most walk-behind blades for this work are wet-cutting blades. Use the one that matches how you are cutting.
- Rental blades are charged separately. Rntr puts blade fees at about $25 to $60 a day, and many yards charge by wear instead. Ask which before you leave, and measure the blade before and after if they charge by wear.
Upcut, downcut, push or self-propelled
Walk-behind saws come in a few configurations, and the rental counter may offer you any of them:
- Downcut vs upcut. On a downcut saw the blade rotates so the teeth enter the slab from the top, which gives a cleaner top edge. EDCO's KL-14 is sold as a downcut model. Upcut saws throw debris forward and away from the operator. For a visible edge next to pavers, downcut is the tidier choice.
- Push vs self-propelled. A push saw moves as you push it; a self-propelled saw drives itself at a set speed. Self-propelled models reduce fatigue and keep the cut straighter over long runs, but they cost more to rent and weigh more. For a driveway apron or a patio cut-back, a push saw is plenty.
- Weight. Rntr lists 14-inch walk-behinds at 200 to 300 pounds and 20-inch models at 500 pounds and up. EDCO's KL-14 is lighter at 132 pounds, with a handle that folds to 31 inches for transport. Ask the weight before you plan to lift it into a pickup.
Gas, electric, and the saw that belongs indoors
Gas saws dominate rental fleets because they need no cord and no generator, and they have the power for long cuts. They also produce carbon monoxide, and a walk-behind saw is exactly the machine that tempts people to cut indoors: a garage floor for a drain, a basement slab for plumbing, a sunroom being converted.
I read the California FACE investigation that shows why this matters. In case report 17CA001, a 34-year-old laborer was cutting plumbing trenches in the slab of a vacant strip-mall store with a used 13-horsepower gasoline walk-behind saw. The night before, with the door open and a fan running, the plumber working with him got headaches. The next day the door was closed and the fan was off. He was wearing an air-purifying respirator with organic-vapor cartridges, which does not filter carbon monoxide. He started around 11:30 am and was found at 4:15 pm; his carboxyhemoglobin level was 69%. The saw had no CO warning label, and the report recommends electric saws only in enclosed spaces.
For a homeowner, the rule is simple:
- Outdoors: gas is fine.
- Garage, basement, enclosed porch or any room with a roof: electric saw, or the job waits. Open doors and a fan are not ventilation for a gas engine, as that report shows.
Electric walk-behinds exist for exactly this. EDCO's DS-18 is electric-only, and several of its other models come in both versions. They need a proper circuit, so ask the rental yard what power the saw draws before you assume a garage outlet will run it.
Water on the blade, and where the slurry goes
A walk-behind cutting dry concrete throws respirable crystalline silica into the air, and silicosis is not reversible. OSHA's silica standard for construction (29 CFR 1926.1153, Table 1) covers walk-behind saws with one engineering control: a saw with an integrated water-delivery system feeding water continuously to the blade. Used outdoors, that is the whole requirement, with no respirator listed at any duration. Indoors or in an enclosed area, add an APF 10 respirator. The rule is written for employers, but the dust doesn't check who is paying.
Most rental walk-behinds have a water tank or a hose connection. EDCO's KL-14 has a misting system, with an optional tank for sites without a hose.
The water turns into slurry, and that slurry is the part people forget. Concrete Cutting Pro notes it is strongly alkaline, around pH 12 to 13, and says it must not go into storm drains. For a homeowner:
- Before you start, plan where the water runs. Keep it away from storm drains, ponds and planting beds.
- Use a wet/dry vacuum or squeegee the slurry into a low spot on bare soil or a lined pit.
- Let it dry, then scrape it up and dispose of it with the concrete debris.
- Rinse the saw and the surrounding pavers or siding before the slurry dries, because it leaves a gray film that is hard to remove later.
Rent or buy a walk-behind concrete saw?
For a homeowner, rent. This is the one position I'd defend without hedging. Rntr lists 14-inch walk-behind rentals at about $120 to $200 a day and 16- to 18-inch models at about $175 to $280, with weekly rates around two to three times the day rate. Concrete Cutting Pro puts buying a walk-behind at $3,000 to $15,000, and says it only earns its keep for someone cutting at least a few hundred linear feet a year. A patio cut-back or a driveway apron is a few dozen feet, done in an afternoon, and the rental includes a machine someone else maintains.
Rental checklist:
- Blade: size, material (cured concrete vs asphalt), and whether it is charged by the day or by wear.
- Water: hose connection or tank, and which fitting it takes.
- Fuel: gas type and whether the tank comes full.
- Weight and transport: whether two people can load it, or whether you need a ramp or trailer.
- Depth stop: ask them to show you how the depth wheel or crank works and where zero is.
- Deposit and cleaning: Rntr mentions deposits of $100 to $500. Return it rinsed; slurry dried on a saw is a cleaning charge waiting to happen.
Flush cuts and the last few inches at a wall
A walk-behind saw cannot cut right up to a wall, a step or a post. The blade sits inboard of the frame and guard, so the cut stops a few inches short. On most saws the blade is on one side of the machine, which gets you closer on that side, so plan your cut direction to put the blade side against the obstruction.
For the last few inches, you have three options:
- finish with a handheld cut-off saw, cutting from the walk-behind's kerf up to the wall;
- rent a flush-cutting saw, a type designed to cut tight to walls, if you have many such edges;
- break out the last few inches with a chisel, if it's on the side being removed.
Cutting a slab line, start to finish
This is the order that works for a straight cut across a patio or driveway slab. The general technique for handheld saws is in our sibling guide on how to use a concrete saw.
- Find what's under the slab. Call 811 a few days ahead if the cut goes anywhere near a service line, and think about what runs under your own slab: sprinkler lines, drain pipes, conduit to a light. A slab saw finds them instantly.
- Snap the line. Use a chalk line and mark it twice, once as the cut line and once 6 inches away as a reference, so you can still see where you're going when slurry covers the first.
- Set up water. Connect the hose or fill the tank, and make sure water flows to both sides of the blade before the engine starts.
- Set the depth for the first pass. EDCO recommends step cutting rather than burying the blade to cut all at once. A first pass of about an inch or two is a sensible start, then deeper passes.
- Start with the blade raised. Start the engine with the blade above the surface, let it reach full speed, then lower it into the cut with the depth control.
- Walk it slowly and straight. Line the pointer with the chalk line, push at a steady walking pace, and let the saw set the speed. If the engine bogs or the blade climbs, you're pushing too hard or cutting too deep for that pass.
- Lift the blade before you stop. At the end of the cut, raise the blade out of the slab before shutting down or turning.
- Clean up the slurry as described above, then break out the side you're removing.
(A useful sign you're doing it right: the saw sounds the same at the end of the cut as it did at the start. A saw that's laboring is telling you something before the blade does.)
Rent a 14-inch wet saw, cut outdoors, step it down
For cutting a slab before pavers go in, a walk behind concrete saw is the right tool once the cuts are long or the slab is thick: rent a 14-inch model for a standard residential slab, confirm the depth against a measured edge, run water on the blade the whole time, step the depth down in passes, and keep gas engines outside. Everything else, from blade choice to slurry, follows from those five habits. Then enjoy the one part of the job that looks like it's in a hardware commercial: the long, straight, perfectly clean kerf.
FAQ
How deep can a walk behind concrete saw cut?
It depends on blade size. A 14-inch blade cuts about 4 1/2 to 5 inches (EDCO's KL-14 lists 4 3/4 inches), an 18-inch blade about 6 1/2 to 7 inches, and a 20-inch blade about 7 to 8 inches.
What size walk behind saw do I need for a patio slab?
For a typical 4-inch patio or walkway slab, a 14-inch saw is enough. Measure the slab at an edge first, and move up to 16 or 18 inches if it is thicker than about 4 1/2 inches.
Can you use a gas walk behind concrete saw indoors?
No. Gas engines produce carbon monoxide, and open doors and fans are not enough ventilation. California's FACE report 17CA001 recommends electric saws only in enclosed spaces. Use an electric walk-behind indoors.
How much does it cost to rent a walk behind concrete saw?
Rntr lists about $120 to $200 a day for a 14-inch walk-behind and about $175 to $280 for 16- to 18-inch models, plus blade fees of roughly $25 to $60 a day or a wear charge.
Should you cut concrete wet or dry with a walk behind saw?
Wet. OSHA's silica standard lists a continuous water feed to the blade as the control for walk-behind saws. Water keeps silica dust down and cools the blade.
Do I need to cut all the way through a concrete slab?
Only if the side you keep must have a clean edge. When removing concrete, a partial-depth cut followed by breaking the slab usually gives a clean enough break along the line.
