Concrete cuts: When, Where, and How to Make Saw Cuts in Concrete

When, Where, and How to Make Saw Cuts in Concrete

By

Juan Rodriguez

Juan Rodriguez

Juan Rodriguez is an award-winning civil engineer with over 20 years of experience doing large-scale civil works projects. He is an expert on new construction, remodeling, demolition, and code compliance. He also speaks at industry forums and has served as a judge for international engineering competitions. 

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Updated on 04/04/23

Reviewed by

Kelly Bacon

Reviewed by
Kelly Bacon

Kelly Bacon is a licensed general contractor with over 40 years of experience in construction, home building and remodeling, and commercial building. He is a member of The Spruce Home Improvement Review Board.

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Fact checked by

Jessica Wrubel

Fact checked by
Jessica Wrubel

Jessica Wrubel has an accomplished background as a writer and copy editor, working for various publications, newspapers and in public libraries assisting with reference, research and special projects. In addition to her journalism experience, she has been educating on health and wellness topics for over 15 years in and outside of the classroom.

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The Spruce / Jacob Fox

Saw cuts are a used to create control joints in concrete, which help control where cracking occurs due to shrinkage. The cuts should be made at a predetermined spacing and only after the concrete has obtained sufficient strength but before internal cracking begins. Therefore, the timing of saw cuts is critical. Determining when to make cuts depends on many factors, including the type of admixtures and aggregate used in the concrete, the air temperature, and the concrete’s mix design.

Tip

Making saw cuts in concrete can be a very technical process: If you’re unclear on the process or project, call a professional.

When to Saw-Cut Concrete

In addition to the concrete mix and the weather conditions, determining when to saw concrete is based on the concrete’s hardness as well as the type of cutting equipment used to make the saw cuts. Cutting too early causes raveling, an effect created by the saw blade pulling the aggregate out of position, leaving a messy, weakened edge along the cut. This also causes undo wear on diamond concrete saw blades. Sawing too late can result in uncontrolled cracking as the concrete contracts during curing.

Saw cutting can start anywhere from three to six hours after the concrete is poured, depending on the weather conditions. The best way to determine whether the slab is ready is to make trial cuts to check for raveling. Saw cutting should start as soon as the raveling stops during these trial cuts.

Some contractors delay sawing to protect their equipment and saw blade to reduce blade abrasion. There are several types of saw blades that can be used, depending on the concrete type and how soon the cuts can be started. Other factors that can lead to excessive blade wear and joint raveling include:

• Pushing the blade too hard
• Saw cutting at high speed
• Using a saw with a bent spindle
• Using an inappropriate saw blade

Where to Saw-Cut Concrete

Before you start saw cutting concrete, is important to select where these cuts will be done. It is recommended to start saw cuts on or at the center of column lines. Joints shall be spaced at 24 to 30 times the slab thickness but this need to be confirmed by a structural engineer. Joint spacing normally ranges between 12 to 18 feet depending on the amount of reinforcement the slab has. If you are using high shrinkage concrete, you might want to decrease the cut spacing. Here are other factors that will help you determine where to saw cut:

• Try to form square patterns
• Make saw cuts continuous
• Select an area that doesn’t have continuous steel reinforcement from one slab or square to another.
• It is better to have smaller cracks than to increase cost by having and maintaining several joints.
• Under hot weather conditions, you might want to try forming a larger square and then cutting interior joints. By doing this you will be controlling fast setting concrete cracks in larger areas.

The Spruce / Jacob Fox

How to Saw-Cut Concrete

Factors such as curing techniques, slab thickness, and base type must be analyzed before selecting where joints should be cut. Once you’ve laid out the joints to be cut, mark them using a chalk line. If you’re using water cutting equipment, make sure that the water is running all the way down to the blade. Allow the blade to reach the required depth, then start walking or moving the equipment following the chalk mark. Here are some recommendations when sawing concrete:

• Do not twist the saw blade.
• Do not let the blade spin in the cut, as this will increase wear on the bond.
• When cutting concrete with heavy rebar, use blades with soft metal segment bonds.
• Always ​​use the required PPE (personal protective equipment).

The Spruce / Jacob Fox

How Deep to Make Saw Cuts

A good rule of thumb is to cut the joints one-quarter to one-third the slab thickness. For a 6-inch-thick slab, that means cutting 1 1/2 to 2 inches deep. Ensure that the saw cut depth meets the structural engineering specifications. If the joint is too deep, aggregate interlocking will not be sufficient to transfer loads. If the saw cut is too shallow, random cracking might occur.

The Spruce / Jacob Fox

The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

1. Guide for Optimum Joint Performance of Concrete Pavements. Iowa State University Institute for Transportation. 2012.

2. Job Safety Analysis. University of North Carolina at Chapel Hill. 2020.

Guide to Cutting Relief Joints in Concrete

 When placing a new slab, making relief cuts in the concrete is crucial to make sure that you don’t have unwanted cracks. If you are newer to concrete placement, this is a key area to understand to make sure that you avoid issues down the road.

 

Before we get into how to make these cuts, I want to go over why they are needed.

 

With any concrete, there is always a chance that you will have cracking because of the potential base material shifting, expansion and contraction due to weather, and other aspects. Making relief cuts ensures that you will have the best chance at limiting large cracks.  

Because of the nature of concrete, cracks will still happen if you make these cuts. The goal is to control where the cracks are.  

 

HOW MUCH SPACE BETWEEN CUTS?

One of the first places to start is knowing how much space you need between your cuts. While experience will help you get a better idea of what works for your concrete and climate, there is a rule of thumb to start with. Cuts should be approx. 2-3 times the thickness of your slab in feet. For example, a 6” slab would have cuts 12’ – 18’ apart.

 

This is strictly a guideline to work from. A structural engineer will be able to confirm what distance it should be depending on environmental factors. Also, if there is a spec on the project, they will most likely tell you what the distance between cuts needs to be.

 

Like I said before, as you continue to get better at cutting, you will find a way or calculation that works best for you.

 

WHEN TO GET ON THE SLAB TO CUT?

This is one of the most crucial aspects when cutting concrete. Relief cutting needs to be done at just the right time to ensure raveling doesn’t occur. Raveling or spalling happens when you get on the slab to early and your saw actually disturbs the aggregate rather than cutting through it. This will leave your cut edges jagged.

 

On the other side, if you wait too long to get on the slab, you increase the chances of random cracking. As the concrete begins to experience shrinkage stresses that exceed the strength of the concrete, there is a lot of “movement” in the slab. If the cuts are not in place before the stressing becomes extreme, the slab has no room to flex resulting in random cracks.

 

The actual time to get on the concrete will be determined many factors (weather, mix, size of slab, ect…) A very rough timeline is somewhere between 1-12 hours. This depends if you are using a wet saw, which needs to wait longer to get on the slab, or an early entry saw which can get on much quicker. Again, this is a variable number for each pour because of the environmental factors that may be at play.

 

HOW DEEP SHOULD A CUT BE?

If you are working on a project with a spec included, there should be a depth listed that you need to achieve. If not, you need to have a minimum of a 1” depth, but you can also base it off the thickness of the slab.

 

A good rule of thumb is to make your cut ¼ the thickness of your concrete. If ¼ of your slab’s thickness, doesn’t reach 1” make sure you still cut at least a 1” depth.

 

WHAT KIND OF SAW TO USE

One thing to be aware of before we go further.

 

When you are looking for saws to do relief cuts, make sure that it is a down cut. In our experience up-cut saws can disturb the aggregate as the blade goes through the slab resulting in raveling. A down-cut saw will be able to solve this and create cleaner edges.

 

This really comes down to a preference decision. A wet or early entry saw will both produce similar cuts, but there are some differences between the two that may help you decide.

 

When it comes to choosing between these types of saws, it all depends on your application. Wet saws are great because they are versatile. They can be used to do other types of floor cutting if necessary. An early entry saw’s sole purpose is for getting on the slab early and doing these cuts. It will save you time, but will not be extremely useful in other cases.

At the end of the day, it comes down to what you are more comfortable with.

 

We hope that this blog helped you get a basic understanding on relief cutting so that you can produce great looking slabs.

 

types and installation of an expansion joint in concrete

Concrete floors are called, which include: binder (Portland cement or liquid polymer), coarse aggregate (crushed stone), fine aggregates (sand, marble chips, granite screenings). Such floors can be prefabricated from factory-made slabs or poured using monolithic technology. In monolithic concrete floors, expansion joints are provided , the purpose of which is to compensate for various kinds of stresses acting on the structure, to prevent its cracking, to extend the operating period of individual constructs and the structure as a whole.

What is an expansion joint in concrete?

An expansion joint is a technological section designed to prevent cracking in concrete structures, to reduce loads on adjacent building structures.

Concrete floor expansion joint is a technological gap in the sub-base, screed or coating, which allows independent movement of individual sections.

The technical parameters of the sections are reflected in the project documentation. Deformation gaps are of several types, their specific type is selected depending on the functional purpose.

• Temperature. Concrete is a material subject to dimensional changes due to temperature fluctuations. The device of expansion joints in concrete is mandatory when pouring the screed over the “warm floor” system. Cracks above the heating elements are especially dangerous, as they can cause pipe rupture, failure of the heating mat or film. The dimensions and spacing of the heat shrink joint in the concrete floor are determined by civil engineers depending on the maximum temperature fluctuations, the base material, the thickness of the mixture, its strength class.
• Shrink . When hardening, the upper layers of concrete seize and harden earlier, and the deep ones later, which causes internal stresses. The thicker the concrete layer and the larger the area of ​​the room, the greater the delamination of the monolith. The task of the device of shrinkage joints is to prevent deformation of concrete due to the occurrence of internal forces. The gap is cut in the screed after grinding.
• Sedimentary . During the settlement of buildings, forces act on the foundation in different directions. Under their influence, interfloor slabs can shift, which leads to floor deformations. It is especially important to provide for sedimentary cuts when pouring concrete mixture on low-strength bases or those subject to freezing / thawing. It is optimal to wait for the building to settle and only then begin the installation of concrete floors.
• Seismic . Serves to dampen multidirectional forces arising from earthquakes. Seismic cuts prevent floor cracks and improve the overall stability of buildings.
• Insulating . This section, which is a type of shrinkage seam, is laid at the junction of vertical building structures to the floor. Compensates for shrinkage of the mixture during hardening. The smallest width is 10 mm. An elastic band is used for filling.
• Structural (delimiter). It is made to distinguish between zones flooded at different times. The incision is filled with sealant.

Temperature, settlement, shrinkage and anti-seismic expansion joints are made not only in floors, but also in other concrete elements of buildings – external walls, foundations, floor slabs.

The decision on the need to manufacture technological gaps depends on the natural and climatic conditions of the region, the geological conditions of the construction site, and the specifics of the functional purpose of the building.

Regulatory requirements for the installation of expansion joints in concrete floors

The definition of expansion joints and the rules for their formation are regulated by SP 70. 13330.2012 (updated edition of SNiP 3.03.01-87), SP 29.13330.2011 (updated version of SNiP 2.03.03- 88), other normative acts.

Basic requirements when creating the deformation protection of the building:

• The seams must be located on the same line with the axes of the columns, the seams of the reinforced concrete floor slabs, special deformation cuts provided in the base.
• For sealing technological cuts, plastic polymeric materials, cement-based compositions of at least grade M400 (CEM I 32.5), bundles, tapes, metal profiles can be used. For grouting joints, the opening of which does not exceed 0.5 mm, low-viscosity cement-based mortars are used.
• Expansion joints inside a monolithic slab, and not just along its perimeter, are made mainly at production facilities.
• Gaps can be formed by special formwork configurations or cut into already hardened concrete. The cut is made two days after pouring the mixture with a tool with diamond discs. During pouring, slats treated with anti-adhesive compounds can be installed in the mixture. After the material has set, the slats are removed, and their location is sealed with filler.
• Technological gaps are located at a distance of 8-12 m from each other, if the base of the floor is a reinforced concrete slab. In other cases, the locations of compensation cuts are determined by engineering calculations and displayed in design documents.

Materials for filling expansion joints in a concrete floor

Various materials are commercially available for filling expansion joints in a concrete floor, the purpose of which is to seal and protect the gap from water ingress, pollution, and stress compensation. The choice depends on the size of the gap, the dimensions of the room, and the operating conditions.

Metal profiles

This is a complex double-sided metal profile with rubber and plastic inserts. It happens overhead and built-in. It is laid at the stage of pouring the concrete mixture. This is an expensive type of filling, it is used only on floors that experience high loads. Usually it is in demand at industrial facilities.

Polymer foam sealing strips or elastic bands

This filler is used in small areas. Stacked in one or more layers.

Profiled belts

Products are made of high strength polymers or modified rubber. They are laid in the concrete mixture during its pouring. Versatile in use.

Silicone Sealants

Used for small areas that do not experience heavy loads. The compositions can be one- or two-component. The former are easy to operate, the latter have better working properties. Silicone sealants are designed to seal gaps made by sawing hardened concrete.

Expansion joints in concrete floors must fully comply with the project, and the technology for their manufacture and filling must take into account the operational features of the facility as much as possible.

what are they and how are they performed?

Contents

• 1 What is an expansion joint?
• 2 Necessity of the device
• 3 What are expansion joints?
• 4 How are they carried out?
• 5 Screed expansion joint
• 6 Conclusion

Concrete bases are the most durable, reliable and strong. However, concrete is a capricious material in the formation of structures, surfaces and their operation. Loads acting on the material and in the material, which have different causes, lead to cracking of the monolithic surface. This happens if measures are not taken in time to create compensatory cuts that prevent such phenomena.

What is an expansion joint?

This is a targeted fragmentation of a concrete base (floor, wall, roof, etc.), which weakens the action of external and internal forces (stresses), leading to uncontrolled deformation and destruction of the concrete monolith to its entire depth. Such deformations can cause a decrease in the performance of buildings. The compensation cut reacts and damps changes in the geometry of a concrete slab, consisting of several independent fragments. Such seams are a serious factor in ensuring the reliability and durability of structures.

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Necessity of the device

Structural elements of buildings are connected and constantly interact with each other against the background of the fact that buildings change geometric dimensions under the influence of changes in the temperature and humidity mode of operation, shrinkage of the frame, precipitation of hardening concrete monoliths. All this causes stresses in the nodes of a single structure of the structure, although often such changes in the geometry of the elements are visually imperceptible. Creating cuts contributes to the uniform distribution of additional loads (forces, stresses) by compensating for changes in the geometric dimensions (expansion, compression, twisting, shearing, bending, etc.) of the material that have arisen due to factors acting on concrete (or in concrete).

Loads always affect structures, but without formed expansion joints, they entail a deterioration in the characteristics of foundations, the occurrence of cracks, manifestations of structural deformations, an increase in internal stresses, a reduction in the duration of operation, etc. For example, heating / cooling walls leads to a slight change in their dimensions, which in turn creates stresses in the material. The larger the dimensions of the walls, the greater the tension.

They cause cracking (in concrete screeds, interior finishes), are transmitted through a rigidly connected frame to ceilings, beams, stairs, foundations, etc. A minimal shift in the position of the wall in the stress center will immediately threaten the integrity of the rigid structure of the building. The duration of impacts, their magnitude can even cause the destruction of the frame of the structure. Shifts and seasonal heaving of soils also appear as a factor in the destruction of the blind area, if they do not provide for temperature cuts.

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What are expansion joints?

Types and purpose of joints in concrete.

The nature of the loads that the cuts must compensate for is the main feature of their classification. They are divided into fixed (conditionally) – technological and shrinkage, as well as sedimentary, insulating and temperature, deformation. Breaks in work with concrete are accompanied by the formation of technological gaps, when a cushion of material, cast earlier, adjoins the edge of a new section of the monolith.

Shrinkage cuts by fragmenting the slab reduce tensile stresses in the hardening material, which facilitates the passage of cracks below the cut without reaching its surface or the passage of a fracture along the seam. They compensate for deformation and shrinkage due to uneven loss of moisture in different areas of the screed. External temperature sections of the building are divided into sections, which protects against deformations caused by changes in the temperature of the concrete.

Often they are complexed with seams, the task of which is to compensate for vertical shifts in certain parts of structures due to uneven settlement of soils under the building. Expansion joints relieve the assembly joints of structural elements from torsional deformations, transverse and longitudinal stresses. They are formed at the junction of the floor to the columns, flights of stairs, ramps, curb stone, at breaks in the planes of the material, areas of stepped height difference of the screeds, etc.

Insulating joints must be created at the junction of the floor with walls, stairs, columns, etc. Their task is to prevent the transfer of deformations (temperature, shrinkage, etc.) from the frame of the structure to the floor screed. This separation prevents the passage of shock sound waves into the premises through the screed and back. Temperature joints are formed to compensate for the movement of soils and buildings relative to the blind area. Its fragmentation and elastic attachment to the foundation provide load damping.

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How are they performed?

Two methods of forming seams using diamond or abrasive wheels are used:

• mounting – when at the pouring stage the concrete is divided into fragments using damping materials laid to the entire depth of the slab (glass, timber, polymer tapes, plastic lining, etc.) , which can be removed from the seam or remain in it;
• cutting – when a hardened concrete slab is cut to a fixed depth, and the formed joints are sealed with polymer sealants, mastics, closed with special structures or left unfilled. The step (width of the strip) of cutting is determined as follows: the height of the screed (in cm) is multiplied by the coefficient “24”. The result is the step of arranging the seams (in cm).

They are made perfectly straight and can only be crossed at right angles. At the same time, the joints of the cuts should not form the letter “T” in the plan. When it is impossible to exclude in terms of the intersection of the seams in the form of a triangle, the figure is made equilateral. Minimum joint width 0.6 cm, depending on the height of the artificial stone layer. On wet concrete, cutting can be carried out already 12 to 72 hours after laying (depending on the air temperature), however, the situation should be excluded when the concrete is completely dry and the cut edge of the material crumbles.

The depth of the sections is 1/4 – 1/2 of the slab height. The floor area inside the premises is considered indivisible (up to 30 m2) when the ratio of the sides of such a “rectangle” is not more than 1:1.5. Large areas are separated by shrinkage seams into similar or smaller areas. When a monolith has a length of 25 m or more, it must be crossed with seams. If the tracks of the hardening material are 3 meters wide or more, longitudinal seams are made.

On slabs open to precipitation, cuts are made in increments of 3 m, and the maximum area of ​​a single piece is not more than 9m2. Monoliths of paths (corridors) are cut by transverse seams with a step of up to 6 m (the usual step is twice the width of laying the material), and L-shaped turns are fragmented into rectangles (squares). Slots also separate floor coverings made of various materials, bases in rooms along doorways, places where the height of the screeds differ.

Such joints, like those under the parquet board, are not filled, but are sealed in the open air. Sections of the floor slabs surrounding the columns should be square in plan, the corners of which are located against the flat faces of the columns (the square formed by the seams rotates 45 degrees relative to the faces of the column). The structural integrity of the dissected bases is ensured by special systems placed in the seams or superimposed on them. These are metal profiles and seals.

In blind areas, wall joints are filled with roofing material, bitumen or sealant. The blind area is subdivided into sections of 2 – 2.5 meters, which are crossed by seams (perpendicular to the wall) to the entire depth of pouring concrete. Such a separator is formed by a board (fixed formwork) laid on edge so that its upper edge coincides with the surface of the formwork. Boards (thickness up to 3 cm) are processed with hot bitumen, a septic tank. Special vinyl tapes up to 15 mm thick are also used. Then the formwork is concreted.

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Expansion joint in screed

Scheme of arrangement of different types of screed joints.

The pattern of the cuts that separate the screed depends on the area and configuration of the room. Wall seams have a depth for the entire height of the screed. They are filled with elastic gaskets up to 10 mm thick, silicone. Also, pouring slabs are cut at the level of doorways and corridors, but not at the entire height of the material.