Types of Concrete Cracks

Concrete free of Cracks       
    This kind of concrete is rare. In the real world, concrete always cracks. Most cracks are caused by the shrinkage of the concrete mix as it cures

Cold Joints
    Occur where two separate concrete pours come together.  These are usually linear, closely joined and bonded.

Control Joints       
    Since concrete tends to crack as it shrinks, control joints are sometimes cut into the slab within a few hours after the concrete is finished to create a "weakened plane". Since concrete cracks generally occur at the weakest point (or the point of greatest stress) this cut in weakened plane "tells" the concrete where to crack, and helps to avoid (as much as possible) unsightly random cracking.


Random cracks       
    These meandering, sometimes linear cracks are generally caused by normal shrinkage (where control joints should have been placed). If the random crack varies in width or is wider than 1/16", check to determine if the crack could be the result of settlement, or dynamic movement.


Expansion Joints       
    Provided on large pours where movement is expected due to design of slabs or other structures. Expansion joints in concrete are generally about *" wide and contain a compressable material in the joint. Sometimes the material is felt or poly-foam. Usually, well designed concrete expansion joints utilize a foam backer rod and flexible caulking or sealant as shown in detail above.

Settlement cracks       
    If the slab is not level on both sides of a crack, settlement is usually the cause. This is a situation in which no tile should even be considered until the cause of the settlement is discovered and corrected.


Heaving cracks       
    A serious situation where the concrete is at a different elevation on either side of the crack. As in settlement cracks, this condition must be corrected before tiling is even considered as an option