- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 17 Nov 2020
Laitance is a weak friable layer of fine particles that can form on the surface of concrete after it has cured and is a common cause of floor failure. It is comprised of hydrated cement and fine aggregates which rise to the surface with the addition of too much water.
It is formed when an abundance of water in the mix creates an upward movement through the concrete. It can also be a result of rain damage during the placing process, or of over-trowelling and excessive tamping, or vibration of the concrete.
The thickness of laitance can be determined by scratching the surface with a screwdriver or other metallic edge until reaching the main aggregate. Thicknesses can vary but are seldom more than 5 or 6 mm. Since laitance has poor adhesion to the actual aggregate in the concrete mix, heavy traffic and impact will delaminate it or cause it to dust away under abrasion.
Methods for removal include:
- Shot blasting: A fast and efficient method that involves firing abrasive elements on the area at high velocity.
- Mechanical planning: Used for thicker laitance and involving a machine with rows of rotating tungsten-tipped cutters.
- Scabbling: A heavy-duty method that involves compressed air tools which vibrate and impact the concrete surface.
- Grinding: Handheld tools are used for smaller areas and edges.
- Acid etching: The acid attacks and breaks down the the top surface. This should only be used if other options have been ruled out.
 Related articles on Designing Buildings Wiki
- Alkali-silica reaction (ASR).
- Concrete repair mortars.
- Concreting plant.
- Construction dust.
- Construction tools.
- Flooring defects.
- How to clean concrete.
- Lime run-off.
- Mould growth in buildings.
- Stratification of concrete.
- The properties of concrete.
Featured articles and news
Survey reveals green skills gap.
America's economic collapse produced scores of PWA Moderne projects.
The benefits of glowing aggregates and cement.
Urgent need for open communication to address mental health issues.
Guidance offered on COVID-19 green recovery, building safety and more.
Providing strength and support above the joists.
Enforcer will test and investigate product safety.
Underfloor air conditioning comes to 24 St James's Square.
Consultation on public right to buy unused public property.
IHBC resource offers improved consistency.
New laws to ‘retain and explain’ historic statues.
The principles and art of the possible. Book review.