Delamination

Delamination is separation of the concrete surface layer from the base, creating hollow-sounding areas that eventually break loose. The surface appears intact initially but sounds hollow when tapped and later spalls or breaks away under traffic.

Why It Matters

Delamination is usually caused by finishing too early—working the surface while bleed water is rising brings weak, watery paste to the top. This creates a layer enriched in cement paste and water with little aggregate, bonded poorly to the stronger concrete below. Once the weak layer delaminates, repair is difficult and costly.

Preventing delamination requires patience. Wait for bleed water to evaporate before finishing operations. Tap the concrete with your hand—if water sheen appears, it's too early. Professional finishers prioritize proper timing over speed.

Technical Details

Delamination causes:

• Early finishing: Most common cause—troweling before bleeding stops
• Rapid drying: Hot, dry, windy conditions cause surface to dry while interior bleeds
• Over-finishing: Excessive troweling brings too much paste to surface
• Dust on surface: Construction dust creates weak bond plane
• Vibrator overuse: Over-vibration causes excessive bleeding

Detection methods:

• Chain drag: Dragging chains across surface produces distinctive hollow sound over delaminated areas
• Hammer sounding: Tapping with hammer reveals hollow areas
• Visual inspection: Delaminated areas often show slight color difference

Repair requires removing the delaminated layer completely—patching over it fails. Proper repair involves scarifying to sound concrete, then overlaying with bonded repair mortar or micro-topping.

Related Terms

• Spalling - Related surface deterioration problem
• Bleed Water - Cause of delamination when finishing too early
• Finishing - Proper timing prevents delamination

Learn More

• How to Repair Cracks - Includes delamination repair methods
• How to Finish Concrete - Proper finishing timing
• Concrete Calculator - Calculate your project volume