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Concrete & Masonryaka: contraction jointaka: crack control jointaka: saw cut

Control Joint

In Plain English

A planned groove or cut in concrete that tells the concrete where to crack so random cracking doesn't appear elsewhere.

Definition

A pre-planned groove or weakened plane cut or formed into concrete flatwork or masonry walls to direct and control the location of shrinkage cracking. As concrete dries and shrinks, it cracks at these intentional weak points rather than randomly across the surface. Control joints in slabs-on-grade are typically saw-cut to a depth of 1/4 of the slab thickness.

Why It Matters in Bidding

Control joints are a small line item with outsized impact on quality claims, so estimators must capture the labor for saw-cutting or tooling plus joint sealant in their concrete and masonry takeoffs. Omitting or mis-spacing them invites random cracking that owners reject, leading to costly callbacks, while the layout and timing of cuts also affect the schedule because slabs must be jointed before uncontrolled cracking begins.

Example

On a 20,000-square-foot warehouse slab, the estimator quantifies linear feet of saw-cut control joints on a roughly 12-by-12-foot grid and adds early-entry sawing labor and joint filler to the concrete bid.

Related Terms

Expansion JointFlatworkCuringTrowel Finish

Frequently Asked Questions

A control joint is a weakened plane that directs shrinkage cracking and allows minor movement within a single placement. An expansion joint is a full-depth gap with compressible filler that separates elements and absorbs thermal expansion and structural movement. They serve different functions, so estimators price and locate them separately on drawings.
A common rule of thumb spaces joints in feet at roughly two to three times the slab thickness in inches, producing panels that are as square as possible. Actual spacing follows the structural drawings and mix design. Estimators should joint-spacing per the plans rather than assume, since wider panels increase random-crack risk.
Timing is critical: joints are typically cut as soon as the slab can support the saw without raveling, often within several hours using early-entry equipment, and before uncontrolled cracking starts. Cutting too late lets random cracks form first, defeating the purpose. This timing window can affect crew scheduling and equipment costs in the bid.

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