What Is Cement Laitance?

Removing cement laitance from new concrete is a critical step in surface preparation prior to sealing or coating. Cement laitance is a weak, powdery layer of fine cement particles and calcium salts that rises to the surface during concrete placement and finishing.

Although laitance may appear harmless, it creates a fragile surface that can severely reduce adhesion and long-term performance of sealers, coatings and membranes.

Why Cement Laitance Forms on New Concrete

Laitance typically forms due to excess water, over-finishing, vibration, or bleeding during concrete placement. The result is a high-cement, low-strength surface layer that is significantly weaker than the underlying concrete.

Why Laitance Must Be Removed

  • Reduces adhesion of sealers and coatings
  • Causes peeling, blistering and delamination
  • Traps moisture beneath surface treatments
  • Creates uneven absorption and appearance

Identifying Cement Laitance

Laitance often appears as a dusty or chalky surface that can be easily scratched or rubbed away. Water may bead unevenly, and the surface may show whitening after drying.

Methods for Removing Cement Laitance from New Concrete

Why Cement Laitance Causes Sealer and Coating Failure

Cement laitance creates a weak, friable surface layer that does not possess the structural integrity of the underlying concrete. When sealers or coatings are applied over laitance, they bond to this unstable layer rather than the concrete itself.

As the laitance breaks down over time, the bonded coating or sealer loses adhesion, leading to peeling, blistering or delamination. These failures often appear weeks or months after application, making laitance a common but frequently overlooked cause of premature coating failure.

Water Absorption Testing After Laitance Removal

A simple way to confirm successful laitance removal is to observe how clean water behaves on the concrete surface. After preparation, water should wet the surface evenly and absorb consistently rather than beading or sitting on the surface.

Uneven wetting can indicate remaining laitance, curing compounds or contamination that may interfere with sealer or coating penetration.

Common Mistakes When Treating Cement Laitance

  • Applying sealers before laitance has been fully removed
  • Over-etching the surface with aggressive acid treatment
  • Failing to neutralise and rinse after chemical removal
  • Assuming new concrete does not require preparation

A controlled, system-based approach ensures laitance is removed without damaging the underlying concrete surface.

Mechanical Removal

  • Grinding or light abrasion
  • Abrasive blasting
  • Mechanical scrubbing

Mechanical methods physically remove the weak surface layer and are often used on large or heavily contaminated surfaces.

Chemical Removal

  • Acid-based treatments to dissolve surface paste
  • Controlled dwell time and agitation
  • Thorough rinsing and neutralisation

Chemical treatment must be carefully controlled to avoid over-etching or damaging the underlying concrete.

Neutralising and Rinsing After Laitance Removal

After chemical removal, surfaces must be thoroughly rinsed and neutralised to stabilise surface pH. Residual acidity or alkalinity can cause adhesion failure if not properly addressed.

When to Remove Cement Laitance

Laitance removal should occur once the concrete has cured sufficiently to allow treatment without surface damage. Timing depends on concrete mix design, curing conditions and the preparation method being used.

Preparing Concrete After Laitance Removal

Once laitance has been removed, the concrete surface can be prepared for sealing or coating. This includes final cleaning, moisture assessment and verification of surface readiness.

For full preparation steps, refer to preparing concrete before sealing.

System-Based Concrete Surface Preparation

Professional surface preparation uses a system-based approach that addresses contamination, surface strength and chemical compatibility.

See our Concrete & Masonry Cleaning Systems for complete preparation guidance.

Technical guidance on concrete surface quality, curing and cement paste behaviour is published by Cement Concrete & Aggregates Australia (CCAA) .