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Most people have a love-hate relationship with concrete. This type of material is great when you need a weather-resistant, heavy-duty, and permanent surface, but not-so-great when you need to cut, repair, or replace it. The whole business of cutting concrete can be pretty daunting, but it doesn’t really have to be. The battle can be won by selecting the correct tool – and in this case, that would be the circular saw. In this article, we’ll be taking a closer look at how this device functions and how to accurately cut concrete with it.
Concrete With a Circular Saw

What’s a Circular Saw?

A circular saw would be a power tool that uses an abrasive or a toothed disc to cut various materials by utilizing the motion spinning around its arbor. It can cut materials such as masonry, metal, plastic, and wood, and can be either mounted to a machine or hand-held. The blades of these devices are specially designed for the material they are intended to be used on and can be powered by electricity, gasoline, or a hydraulic motor. The circular saw first appeared somewhere at the end of 18th century when it was used to transform logs into timber. There are many claimants to the invention of this device, but the person most commonly accepted as its inventor is Samuel Miller, who obtained a patent all the way back in 1777. The rotary nature of this handy device requires more power to operate – but it’s highly efficient since its teeth are in perpetual motion. The sound of this machine is different than that of the up-and-down saw, which is precisely what earned it the nickname of the buzz-saw.

The Types of Blades

In this part of the article, we’ll have a look at the different types of blades used for circular saws and what are they good for:

Abrasive Corundum Masonry Blades

These types of blades are typically quite inexpensive – a 7″ blade will cost you under $5. They are widely available and can be used for cutting asphalt, stucco, as well as concrete. Unfortunately, the low price of abrasive corundum blades has a negative effect on their speed, as they’re capable of cutting only the shallow 1/2″ to 1/4″ passes. Cutting with them can be quite time-consuming, and they also wear away fairly quickly.
Abrasive corundum masonry blades
A 7″ abrasive corundum blade will wear down to 6 1/2″ after you cut a foot or two along your cutting line. This means that the operator has to frequently modify the depth of the saw in order to expose more of the blade. These types of blades create plumes of dust and usually get so hot to the point where they glow. But they’re still the best choice for those with lower budgets and for those that only need to make a couple of shallow cuts.

Diamond Blades

These types of blades sport a metal blade that’s coupled with a diamond or metal composite. When used, their metal composite will slowly wear away and reveal a fresh and sharp diamond edge. Purchasing a diamond blade for your 7″ circular saw can be an ample investment, but you can be sure that it will outlast an abrasive-type blade – it’s a perfect choice for those that cut a lot of concrete.
makita diamond blades
They can be separated into two distinct categories:

  • Dry-Cutting Diamond Blades

These usually come with toothed or serrated rims that help them eject waste and cool the blade. They’re exceptionally great when used for making a number of increasingly deeper cuts. Their biggest downside is that they create a lot of fine dust. When used indoors, one has to seal off the whole working area with duct tapes.

  • Wet-Cutting Diamond Blades

These come with either a smooth perimeter or with standard teeth, with water cooling the blade and keeping the dust away. Cutting with them is fast and clean, but the only proper way to use a wet-cutting blade is to put it into a saw that can distribute water. A workaround would be to plug the device into a GFCI-protected cord and let someone direct a stream of water in front the machine as you’re using it.

How Soon Can I Cut Concrete?

The timing depends on several different factors, some of which are the weather conditions, the type of your blade, the hardness, the aggregate size and the concrete mix design. Those who start cutting too early will most likely experience raveling, and those that do it too late are sure to see some uncontrolled cracking. If the weather is hot, the cutting should start somewhere after one hour, although that also depends on how the concrete is reacting. Of course, the operator could do some trial cuts and try to determine if the material is ready for saw cutting. If the piece is too big, the wisest decision would be to have a couple of saws working at the same time. Some contractors like to delay the whole process in order to protect their tools and reduce abrasion. The above mentioned types of blades can be used depending on how fast the cuts could begin and on the current state of the target concrete. Avoid the following actions:

  • Saw cutting at high speeds
  • Using the inappropriate type of blade
  • Pushing the device too hard
  • Using a saw that sports a ben spindle
Cutting Concrete

Determining Where to do the Cutting

Before you start the whole process, it’s of crucial importance to choose the areas where you will perform the cuts. We recommend starting at the center of the column lines. Joints should be spaced at 23 to 35 the piece’s thickness, although this has to be first confirmed by an engineer. Typically, the joint spacing ranges between 10-18 feet, depending on the volume of slab’s reinforcement. Those using high-shrinkage concrete might want to lower the cut spacing. Here are some actions that should help you choose the areas for cutting:

  • Make saw cuts continuous.
  • Form square patterns.
  • Choose areas that don’t have consecutive steel reinforcement from one square to the next one.
  • It’s always better to have tiny cracks than to raise the cost by maintaining a couple of joints .
  • If the weather is hot, you could try forming a bigger square, and only then cut the interior joints. This will help you control the cracks that quickly appear in larger areas.

How to Do the Cutting

Once you know which joints are to be cut, you should mark them with chalk. If you’re about to use water cutting, you’ll need to have water running down to your blade. Always allow the blade to reach the needed depth and then start to slowly move the device while following the chalk line. Take a look at some additional recommendations:

  • Never twist the blade
  • Never let the blade spin while it’s in the cut since that increases the wear
  • When you’re cutting with heavy rebar, you should use blades that sport soft metal segment bonds

How Deep Should the Cut Be?

In our experience, a good rule is to always cut the joint 1/4 to 1/3 of the piece’s thickness. Always check that the depth of the cut is sufficient enough and that it’s according to the recommendation of the engineer. If it’s too deep, the interlocking simply won’t be enough for the transfer of the loads. If it’s too shallow, there’s a great chance for the random cracks to occur. Factors like slab thickness and length, base type, and the curing techniques all need to be analyzed before choosing where to cut the joints.

How Deep Should the Cut Be

Frequently Asked Questions

What type of blade do I need to cut the sidewalk?
Your best option is to use a large circular saw that sports a diamond blade – you can simply rent one. Maybe you’ll also have to use a jackhammer or a sledgehammer if your circular saw doesn’t cut through the entire thickness of the sidewalk.
I'd like to cut 4-inches thick concrete. Will I have to cut the whole 4 inches of it?
No, you won’t have to. You can cut just the first 2″ with the saw and then simply use a jackhammer for the rest of it. In this way, you’ll prevent your device from overheating.
How do I cut the top of a piece of concrete in a way that will make it level with the part that's next to it?
You don’t – you just have to remove and then re-pour one of the pieces in order to match the piece you like the most.
That’s it – with these tips in mind, cutting concrete should no longer be a trouble for you. Just make sure to use proper safety equipment when you’re cutting – you don’t want to end up in the hospital just because you wanted to complete the project as quickly as possible. And one more thing – always let the weight of your saw do the work for you, without trying to force the blade into the cut. We’ve seen far too many accidents happening because of that, and we don’t want to see such a thing also happening to you.