Often asked: When Should You Cut Control Joints In Concrete?

Joints should be sawed as soon as the concrete can withstand the energy of sawing without raveling or dislodging aggregate particles. For most concrete work, cutting should take place within the first 6 to 18 hours and never beyond 24 hours.

Are control joints necessary?

There is a reason control joints are considered essential for whatever projects you have in design. Thermal expansion and contraction will occur in buildings – that’s a given – and control joints help prevent resulting cracks and damage. Control joints relieve these stresses by allowing for movement.

Why do you cut lines in concrete?

To prevent sidewalks from cracking in random spots and breaking apart, builders make lines in sidewalks. The technical term for sidewalk lines is contraction joints. Contraction joints are placed in fresh concrete before the concrete dries and has a chance to create its own joints, which we call cracks.

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Where do you cut expansion joints in concrete?

It is recommended to start saw cuts on or at the center of column lines. Joints shall be spaced at 24 to 36 times the slab thickness but this need to be confirmed by a structural engineer. Joint spacing normally ranges between 10 to 18 feet depending on the amount of reinforcement the slab has.

How often should you control joints?

The control joint could be spaced every two floors, however, the size of the shelf angle and the width of the joint would have to be larger. A 3/8 to 1/2 inch (10- 12mm) wide joint is satisfactory for control joints every 10 ft.

How do I keep my concrete slab from cracking?

If you’re having new concrete poured consider the following ways to prevent cracking:

  1. Start with a sound subgrade. Make sure the subgrade is compacted.
  2. Modify the concrete mix. Use a low water-to-cement ratio.
  3. Install joints. Be active in deciding where control joints will be placed.
  4. Properly cure the concrete.

How deep do you cut control joints in concrete?

Cut joints 25% of the depth of the slab. A 4″ thick slab should have joints 1″ deep. Groover tools cut joints in fresh concrete. Saw cutting cuts joints as soon as the concrete is hard enough that the edges abutting the cut don’t chip from the saw blade.

How many times do you float concrete?

Push the bull float in one direction only across the concrete, keeping its front edge slightly above the surface by raising or lowering the handle. Two or three times is enough. Don’t overwork the concrete or you’ll weaken it by drawing too much sand and cement to the surface.

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What is the difference between control joint and expansion joint?

In building materials, a control joint is used to control cracking while an expansion joint is designed to handle structural movement. A control joint can be formed during placement of the building material or cut after the material is placed.

How soon can you walk on concrete?

After 24 hours, you can walk on your newly poured concrete, but avoid dragging your feet, ‘doing the twist’, or allowing your pets to walk on it as their claws can scuff the concrete.

How often do you need expansion joints in concrete?

Every concrete slab, inside (basements, garages, etc.) or outside (driveways, patios, entries, etc.) are required to have joints every eight feet horizontally and vertically. Expansion Joints provide space between concrete slabs as a buffer for expansion on hot days and contraction when it is cold.

What is an isolation joint in concrete?

An isolation joint is a separation between adjacent sections of a concrete structure to allow relative movement in three directions and through which all of the bonded reinforcement is interrupted.

How big can a concrete slab be without control joints?

Rule #1 – Keep joints as square as possible. Rule #2 – In order to prevent intermediate cracking, space joints (in feet) no more than 2 – 3 times the slab thickness (in inches).

Does rebar prevent cracking concrete?

Steel reinforcing bars and welded wire reinforcement will not prevent cracking. Reinforcement is basically dormant until the concrete cracks. After cracking, it becomes active and controls crack widths by restricting crack growth.

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Where should masonry control joints be placed?

In vertically reinforced masonry walls with masonry lintels, vertical control joints should be located between openings, or at least 24-inches away from the opening – not to exceed 25-feet on-center (Figure 1).

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