What Is Screed Laitance and How Do You Remove It?

Laitance is the weak, powdery layer that forms on the surface of cement-based and anhydrite screeds as they dry. It consists of fine cement particles and mineral salts drawn to the surface by rising water during the drying process. If not removed before floor finishes are applied, laitance causes adhesive failure, tile debonding, and resin floor delamination. It is one of the most common and most preventable causes of floor finish failure in UK construction.

How to Identify Laitance

Laitance is visible as a dusty or chalky white layer on the screed surface. It can be identified by scratching the surface with a key — if it scratches easily and produces fine white powder, laitance is present. On anhydrite screeds, laitance is always present to some degree and must always be removed. On sand and cement screed, laitance is common but not universal — it depends on the water content of the original mix.

How to Remove Laitance

Laitance is removed by light mechanical abrasion — typically sanding with a floor sander or grinding with a diamond-disc grinder. The process must expose the aggregate below the laitance layer without damaging the body of the screed. After removal, the floor should be vacuumed thoroughly and primed before adhesive is applied. For large commercial areas, specialist floor preparation contractors use ride-on grinding equipment. For smaller residential areas, a standard floor sander is sufficient.

When Must Laitance Be Removed?

Laitance must be removed before: any adhesive-fixed floor finish (tiles, LVT, engineered timber, vinyl), resin floor coatings, and self-levelling underlayments. It does not need to be removed before floating floor finishes that sit on top of the screed without adhesive. For anhydrite screed, laitance removal is mandatory and must be carried out before priming and bonding any finish.

screeding.com provides laitance removal guidance notes with every completed project. If you are unsure whether your screed needs preparation before your chosen floor finish, contact us and we will advise you.