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Isolation joints
Construction joints
Contraction joints
Where to Locate Joints in Concrete Slabs
Be active in deciding where to place control joints
Joints in commercial floors
Decorative joints: Tips for placing joints in decorative concrete
Special Considerations for Installing Joints
Load transfer- Transferring loads across joints
Sealing joints- Tips for sealing and filling joints
Jointless slabs- Reducing or eliminating joints
Related Information:
How to build high-quality slabs on grade
Grooving tools for forming joints
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Super-Krete
Spring Valley, CA

A cleanly sawed joint detracts very little from the appearance of a stamped slab. Super-Krete International

Decorative concrete flatwork still needs joints to prevent cracking, which will be even less acceptable than in typical gray concrete. Isolation joints and construction joints in decorative concrete are exactly the same as with any other concrete.

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Husqvarna
,

This beveled blade turns a standard saw cut joint into a decorative element. Husqvarna Soff-Cut.

Here are a few tips for making contraction joints in decorative concrete:

  • Don't confuse a stamped pattern or an engraved pattern with a joint—stamped patterns and engraving cuts are not deep enough to create the weakened plane for a contraction joint. Make sure the joint depth is at least ¼ the thickness of the slab.
  • Spacing and layout of joints for stamped concrete is identical to any other type of concrete.
  • For stamped concrete, if the pattern has straight lines, such as slate, brick, or wood patterns, cut your joints to follow the stamped pattern as much as possible. Joints can vary in location a few inches or even a foot or two without leading to cracks. Some stamping contractors use custom-fabricated chisels to cut joints into the stamped pattern.
  • For fieldstone or cobblestone patterns, a joint cut to follow the stamped pattern is unlikely to function properly, since shrinkage movement is not always perpendicular to the joint. Any movement parallel to the joint would likely lock the joint, leading to uncontrolled cracking.
  • With stamped concrete, perhaps the best way to cut joints is with a cutoff saw. The irregular surface makes a rolling saw difficult to control. For tips on this, check out Bob Harris's video or get a copy of his Guide to Stamped Concrete—joints are covered in Chapter 23.
  • Saw-cut contraction joints are ideal for decorative concrete because the joint is narrower and cleaner than a tooled joint.
  • Early-entry saws make a nice, clean cut for decorative concrete joints. Soff-Cut's 150D saw is designed for decorative cuts.
  • Soff-Cut also makes a beveled blade that is used on the second day to turn a typical saw cut joint (or early entry joint) into a decorative joint. Read more about Soff-Cut's Ultra Early Entry Concrete Cutting Saws and Diamond Blades.
  • For bonded overlays, cut joints exactly to match the joints in the base slab. No additional joints are needed.
  • For unbonded toppings, ACI 360R-06 recommends the following: "For a thin, unreinforced, unbonded topping slab, additional joints should be considered between the existing joints in the bottom slab to help minimize the curling stress in the topping slab. The topping slab can have high curling stress due to the bottom slab being a hard base for the topping slab. Also, any cracks in the base slab that are not stable should be repaired to ensure they will not reflect through into an unreinforced topping slab."
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