Whether you are installing a concrete surface in your kitchen or workshop or repairing a driveway or sidewalk, concrete can be a challenge to cut. It is a hard material, designed to withstand the elements, so when cutting concrete with a saw, it is no wonder it strikes fear into the hearts of many people.
We take you through the steps of cutting concrete with a saw to show you how to achieve the best results.
When Should You Cut Concrete?
The answer to when depends on several factors. It depends on the type of concrete you are cutting and how hard or abrasive it is. When did the concrete set? This is important because newly poured concrete shouldn’t be cut for at least 12 to 24 hours.
The weather plays a role in when to cut concrete. On hot days, the concrete reacts differently and sets faster, so you may start cutting just 4 hours after setting. If you are unsure, make a test cut and see if you experience cracking or raveling, which is the process of disturbing the aggregate under the surface of the concrete.
Most professionals like to delay the cutting for as long as possible to preserve the integrity of the concrete and reduce the wear on their tools.
Where To Cut Concrete
If you are cutting larger sections of concrete, like a driveway, determine where the joints are. Joints are typically 25 to 35 times the thickness of the slab. A typical joint spacing would be 10 to 18 feet, depending on the level of reinforcement the slab has.
Other questions to consider when cutting concrete are:
- Can you form square patterns?
- Can you make continuous cuts?
- Are you cutting an area with reinforced steel rods joining one slab to another?
What Type of Saw Blade Should You Use?
You can use abrasive masonry blades to cut concrete, but they dull very quickly. Sure, they are a lot cheaper to buy than other specialist blades, but the end result will be that you spend as much replacing these blades as you do on one designed for the task.
Diamond blades have no teeth and come in segmented or continuous rim varieties. They have a diamond grit coating around the cutting rim of the blade that is extremely hard-wearing and resistant to high temperatures. They outlast abrasive blades but cost considerably more.
Dry Cutting Diamond Blade
These are typically the segmented variety to help scoop out the debris as the blade cuts. It keeps them cool and eases the passage of the blade through the concrete. Because they are dry cutting blades, you should expect a lot of dust. You will need to seal the room with duct tape if you are using this tool indoors.
Wet Cutting Diamond Blade
These typically have a continuous rim and stay cool with a stream of water. This lubrication helps to wash away the debris and ease the blade through the material. These wet blades create less dust, but you do need a saw that distributes water. Alternatively, you could get someone to stand over you with a hose to direct the water.
How to Cut Concrete With a Saw
Before we get into the “How,” we need to tackle the “What.” Specifically, what equipment you will need. Here’s a list to make it easier.
What You Need
- 1-inch thick guide board strip.
- Drop cloths.
- Duct tape.
- Chalk or a chalk line.
- Garden hose.
- Wet/dry vacuum.
- Claw hammer (optional).
- Masonry chisel (optional).
- Dry cutting diamond blade.
- Wet cutting diamond blade.
- Ground fault circuit interrupter-extension cord.
- Long pants and a long-sleeved shirt.
- Shin guards.
- Knee pads.
- Steel toe boots.
- Ear defenders.
- N95 face mask (filters out 95 percent of harmful particles in the atmosphere).
1. Decide Which Blade to Use
A dry blade allows you to use your standard circular saw. It means you don’t have to rent a wet saw or a “walk-behind” to give you a continuous stream of water. The downside with a dry blade is the cutting depth. At best, you are going to get a depth of 2.25 inches to 3 inches, depending on the size of the blade.
A wet cut blade extends that depth to between 4.5 inches and 8 inches. It means you can make clean cuts all the way through the material without needing a chisel or a hammer. You also get a longer, continuous cutting motion for cleaner cuts. Plus, the blade is water-lubricated, so there is no need to keep stopping to let it cool down.
2. Preparing the Work Space
If you are working indoors, tape up doors and air intakes using the drop cloths and the duct tape. This stops the dust from escaping or finding its way into places where it could cause damage or contamination.
3. Mark the Line
Using a chalk line or the chalk, mark the line on the slab where you want to cut. A chalk line is better for longer, straighter lines.
4. Protect Yourself
Put on all the safety equipment listed, and make sure you are wearing the correct clothing. Safety is paramount when using heavy machinery to cut hard surfaces like concrete. Also, the dust created is highly toxic and damaging to your lungs if inhaled.
You should also plug your saw into the GFCI-extension cord to protect yourself against power surges or the saw shorting out due to the presence of water.
5. Get the Hose
Lay the hose so that the water trickles over the surface you are about to cut. It should only trickle out of the hose because you don’t want all your equipment to get saturated. Electricity and water don’t mix.
If you are cutting vertically, you may need to get a friend to hold the hose.
6. Set Up the Saw
Lay the 1-inch thick guide board along the line. Now lay your saw at the point where you feel most comfortable starting and set the depth of the blade to 0.50 inches. This is the best depth to keep control of the saw and allow the blade to stay cool.
7. Power Up the Saw
Start up the saw, making sure that the motor is on the lowest revolutions per minute (RPM) setting. Begin your first cut along the line using the guide board for accuracy. Move slowly and never force the speed of the saw. Maintain a two-handed grip to add stability.
Always let the saw work at its own pace and never force the blade deeper than the saw wants to let you. At this point, a 0.25-inch cut is fine. It keeps the line accurate and gives you a template to make deeper cuts later.
8. Remove the Saw
Remove the saw from the concrete and allow the blade to spin freely. This helps to shake free any debris from the blade and remove clogged dust in the saw. Always give the saw blade time to cool down.
9. Remove the Guide Board
Remove the guide board and reinsert the saw blade into the 0.25-inch cut. Work along in 45-second bursts, keeping the cuts nice and shallow. Slowly, that cut will deepen to 2 inches.
10. Collect the Dust
Despite the water washing away most of the dust, it will still collect. Use the dustpan to sweep it away. If you get more debris than you bargained for, use the wet/dry vacuum to keep the work area clean.
11. Adjust the Blade
Shut off the saw and increase the blade depth by 0.50 inches, using the depth lever. Repeat steps 7 and 8, working carefully along the line of the cut. Once you reach the maximum depth your saw allows, remove the blade from the concrete and switch off the saw.
If you were using a “walk-behind” wet saw, you will probably have cut clean through the material and can skip the next steps.
12. Use the Sledgehammer
Clean up the work area using a dustpan and brush or the vacuum cleaner. Keep your protective equipment on and grab the sledgehammer. Start by hitting the area 1 to 2 inches in front of the cut.
Use as much force as the concrete allows, but don’t swing the hammer like you are Thor, the god of thunder. As the concrete falls away, use the pry bar to remove any stubborn chunks of concrete.
Once you have removed the concrete along the line, use the hammer and chisel to chip away at any jagged edges. Place the chisel blade flush with the concrete and hit the top with the hammer. Each blow should be firm enough that the concrete comes away in small chunks.
If you are pouring new concrete into the gap, leave the edges as they are to give the new concrete something to bond to.
13. Time to Clean Up
Clean away the concrete, and either use it as fill in the garden or take it to the landfill to dispose of it correctly.
How Deep to Cut Concrete?
You should aim to cut about a half or a third of the concrete’s thickness. If you cut too deep, the interlocking won’t be enough to bear the loads, and if it is too shallow, you might see cracks appear.
Tips for Cutting Concrete With a Saw
- Choose the Right Blade: Without a shadow of a doubt, the number one tip is to choose the right blade. Either wet or dry, a diamond cutting blade is the preferred choice for the best results.
- Score a Line: Some people extol the virtues of cutting a guideline with a chisel first. It gives your saw blade something to grip into and keeps the saw cutting straight.
- Get the Timing Right: Unset concrete is difficult to cut, while hard set concrete is prone to fracturing. The secret is to cut it while it is half cured. The cut will be smoother with less dust.
- Tape the Saw: Put duct tape on the base of your saw to prevent it from scratching the surface of the concrete as you cut. This is especially important when cutting polished concrete surfaces.
- Don’t Force the Blade: Allow the saw to dictate the pace it moves. Never force the saw to work faster as this will result in resistance and strain on the saw. You also run the risk of veering off course. Keep the RPM low and guide the saw as it cuts.
The Concrete Truth
Like most challenging tasks, sawing through concrete takes a systematic approach.
With the right planning and a slow pace, it can be surprisingly easy to achieve great results. Don’t fear cutting through concrete; embrace it.