How to Cut a Trench in a Concrete Slab? (5 Steps)

In this article we will answer the question, “how to cut a trench in a concrete slab?”. This will discuss the step-by-step instruction on how you are going to cut your existing concrete slab to create a trench for installation of your plumbing, drainage, electrical conduit, garage floor drain and other utility purposes.

How to cut a trench in concrete slab?

Whether you are trying to install a new plumbing or repair a drainage system or any other projects that involve cutting a channel or trench in your concrete slab here are the steps you can follow to guide you in this project.

Materials you Need:

Step-by-step instruction:

Step 1: Check the area where you would like to cut the trench.

Before you proceed to the preparation of the materials you need and planning, you have to check the area first where you will cut the trench drain or channel. If available, obtain the mechanical blueprints of the area. Check if there is any electrical or plumbing underneath the concrete slab especially if there is any radiant in-floor heating, accidentally cutting the coils can destroy the entire system. 

Step 2: Determine the best equipment for your project.

Identify the best saw that will do the job effortlessly and successfully based on the thickness of your concrete. Residential concrete floors are commonly about 4 inches thick and contain steel reinforcement in the form of steel mesh and steel rebar. The best equipment to cut residential concrete floors is with the use of a diamond-blade wet concrete/asphalt saw. You don’t have to buy this equipment if you are just going to use it once, you can rent this equipment in rental centers near your location. Also, you need to prepare a small sledgehammer and a narrow-blade shovel handy. 

Step 3: Dust management

Cutting concrete means that the job will get dusty. Before proceeding to cutting a trench or channel drain in your concrete make sure that you have proper dust management especially if you are working indoors. Jobs that require indoor operation can accumulate dust inside that can be dangerous to your health and can damage appliances or other equipment in your house. Common way to manage your dust is to use plastic sheeting and duct tape to seal off the space before cutting.

It is also preferred to use a wet saw in doing the job to reduce the amount of air borne dust in your area. Wet cutting involves pouring water into the mix effectively reducing the amount of dust up to 85% as compared to dry cutting.

Step 3: Prepare safety clothing.

Since you will be dealing with dust and you will use heavy duty, sharp, and noisy equipment like the sledgehammer and the wet saw, make sure that you have protective and safety clothing to wear while doing the job. Prepare safety glasses, filtration mask, steel-toes boots, hearing protection, gloves, and knee pads and shin guards.

Step 4: Mark the cut you need to make in your concrete.

Using tape measure, measure the length and width you need for the trench. Then mark them using a pencil or chalk outline each the perimeter of the trench you are to cut. When using chalk it is better to strike the lines repeatedly making the mark more thick and bold as possible so it will be easier for you to identify the mark.

In creating a cut for your trench in which the purpose is for drain lines make your configuration as simple as possible. Avoid sharp corners, twists, and turns whenever possible to reduce the possibility of clogging.

Step 5: Create a guide cut

Set your equipment and wear your protective gear for it is time to get the work. Create first a guide cut, do not proceed on cutting the concrete deep already. This can be dangerous because concrete debris may fly and it can damage your circular saw. Adjust the depth of your saw blade to cut to just approximately half an inch deep.

Cutting a shallow line will help you to estimate the hardness of the concrete allowing you to adjust the saw accordingly. It will also be easier to control your saw when you first cut a shallow line. You can do this for not more than 45 seconds because the blade can get hot fast due to friction with the concrete.

Step 4: Cut the concrete

Cut the concrete as based on your guide cut, rotate the depth handle to lessen the blade sharpness if needed. Slowly push the saw forward until the first edge of the trench is cut. Raise the blade then pull the saw back to the end of the trench and cut the second edge similar to what you did with the first edge. The picture below shows what a good concrete cut for the trench.

Step 5: Dig the soil underneath.

Once done cutting use a sledgehammer to carefully break the concrete strip into chunks then remove the concrete pieces exposing the sand or soil underneath your concrete slab. Remove the sand or soil by digging the remaining trench. You can also use jackhammer, this is better for larger jobs, however, this is more expensive than the sledgehammer. These large jobs include digging tunnels underneath pavement or sidewalks or for installation of large pvc pipes for drainage systems.

Cost of Cutting a Concrete

For cutting concrete alone, you will need a minimum cost of $250 and will vary depending on the equipment that you will use. Electric powered slab sawing is about 40% more expensive for the same depth a circular saw can cut. 

For trenching, the average cost is $800, but for small projects it can only cost $400 while $1,200 for bigger projects. Additional cost is also required depending on the use of your trench for example installation of lawn sprinklers or drainage system on your property. If you’re going to use PVC pipe to your conduit the price is about $0,25 per foot. For water lines, you can use copper which costs between $10 to $20 per foot. For gas lines,  a 1-inch polyethylene can be used amounting to $0.66 per foot.

Furthermore, if you hire a contractor to do the job it will be another separate cost.

Conclusion

Installation drainage systems, electrical conduit, or just repairing existing utility piping or tunnels may require you to cut your concrete floor and create a trench. Depending on how big your project is, there are different tools you can use to successfully do the work. Always, make sure that when doing heavy jobs like this to wear your protective clothing and other safety equipment. This kind of job has a possible danger of dust inhalation, therefore, if you can do methods that can lessen the dust generated do so such as wet cutting.

For any questions and suggestions about this article, please feel free to submit your thoughts in the comment section below.

FAQs: How to cut a trench in a concrete slab?

How to cut a concrete floor for new plumbing?

Using a concrete wet saw with a diamond blade cut along the marked concrete. After cutting, use a sledgehammer to break the concrete strip carefully and remove the pieces of concrete produced while cutting. Dig in the remaining trench to remove the soil or sand before running the new plumbing once the concrete was detached. 

Can you cut through concrete?

Yes, you can cut through a concrete as long as you have a diamond blade. In cutting your concrete, you also have to make sure that you have proper safety gears and observe safety precautions. Abrasive blades can also be used to cut concrete, however, this blade wears out quickly and you have to replace it frequently during the course of your job.

How long does it take to cut a concrete slab?

Once the concrete is poured, you have to wait for four hours during hot weather conditions to cut the concrete. On the other hand, it required at least 12 hours during cold weather conditions. If you are in a hurry you can check if it is ready for cutting by making trial cuts and check for raveling.

Do I need an expansion joint in concrete slab?

Expansion joints are seldomly needed. For interior slabs, expansion joints are not needed since inside like your homes, it never gets that hot enough that will cause your concrete to expand much. It is seldomly needed for pavements since it is in an open area, contraction joints open enough accounting for temperature expansion. Exemption of this is when the pavement is next to a building of a bridge, a wider isolation joint of about ¾ inch can be installed.

Can I use an angle grinder to cut concrete?

Angle grinder can be used to cut small concrete. It can also be used to cut granite, bricks, tiles, marble and other materials. If you have to cut concrete using an angle grinder you need a diamond-stud rim balde with ventilation grooves. For cutting ties, a diamond-studded rim balde can also be used but doesn’t require the grooves.

REFERENCES:

How to Cut a Trench in a Concrete Slab. (n.d.). Upgraded Home. Retrieved from: https://upgradedhome.com/how-to-cut-a-trench-in-a-concrete-slab/#:~:text=To%20cut%20a%20trench%20in%20a%20concrete%20slab%2C%20it%20is,amount%20of%20concrete%20dust%20created.

Machin, W. (n.d.). How to Remove Cement to Install Drain Pipes. SF Gate. Retrieved from: https://homeguides.sfgate.com/connect-laundry-sink-washing-machine-same-drain-30305.html

Baylor, C. (n.d.). How to Cut a Shallow Channel into a Concrete Floor. SF Gate. Retrieved from: https://homeguides.sfgate.com/cut-shallow-channel-concrete-floor-52765.html

How to Cut a Ceramic Floor with a Masonry Miter Saw (2019, February 18). Sima. Retrieved from: https://www.simasa.co.uk/blog/masonry-saws/how-to-cut-ceramic-floor-masonry-miter-saw/

How to Cut a Trench in Asphalt or a Concrete Slab (2020, July 19). Sima. Retrieved from: https://www.simasa.co.uk/blog/floor-road-saws/cutting-trenches-in-concrete-or-asphalt-with-a-floor-saw/

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Isolation Joints (n.d.). Concrete Network. Retrieved from: https://www.concretenetwork.com/concrete-joints/isolation-joints.html

Can an Angle Grinder Cut Concrete? (n.d.). CMP Stonemason Supplies. Retrieved from: https://cmpstone.com.au/can-an-angle-grinder-cut-concrete/

Concrete Cutting and Sawing (n.d.). Concrete Sawing & Core Drilling. Retrieved from: https://cutitoutconcrete.com.au/concrete-sawing/

Utility Cut. (n.d.). ACPA’s Concrete Pavement Wiki. Retrieved from: https://wikipave.org/index.php?title=Utility_cuts

Trenching Cost. (n.d). Home Advisor. Retrieved from: https://www.homeadvisor.com/cost/landscape/trenching/#:~:text=The%20average%20cost%20to%20dig,range%20between%20%244%20and%20%2412.

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