Surface preparation
Screed Sanding and Laitance Removal
The fine, weak skin on a cured screed has to come off before anything is bonded to it. Sanding removes it and gives adhesives a sound surface to grip.
Need a screed sanded before tiling?
Name, phone, email — we'll reply the same working day with a fixed price.
Or call our landline on 01392 237700
Laitance is the fine, weak layer that forms on the surface of a screed as it cures — most noticeably on anhydrite screeds, where a thin skin of fines rises to the top. Left in place, it stops tile adhesives and levelling compounds bonding properly and slows the floor's drying.
Screed sanding removes that layer. On the anhydrite floors we pour, sanding the laitance is part of the laying process before bonded coverings go down. Where a screed was laid by someone else and the laitance is still on it, call 07791 510849 and we will talk through what the floor needs.
This page explains what laitance is, why removing it matters, and how screed sanding is done. For the anhydrite-specific detail, see laitance removal on anhydrite screed and the laitance treatment decision guide.
What laitance is and why it matters
As a screed cures, the finest particles in the mix migrate to the surface and form a thin, weak skin. On anhydrite screeds this laitance is pronounced enough that manufacturers require it to be sanded off before bonded coverings. Cement-based screeds and concrete slabs form their own surface laitance too.
The problem is bond strength. Tile adhesive or levelling compound laid over laitance bonds to the loose skin rather than to the body of the screed, and the skin can shear away later — taking tiles or compound with it. Removing the laitance also opens the surface so the screed can keep drying evenly; see surface laitance and dusting for what happens when it is left.
Signs a screed still has its laitance
- A fine, dusty layer that scrapes away with a coin or a nail
- Water beading on the surface rather than soaking in
- The tile adhesive or levelling compound instructions calling for the surface to be sanded
- A screed that has cured but has never been mechanically prepared
How screed sanding is done
- 1
Let the screed cure
Sanding happens once the screed has cured enough to work on — timing follows the screed manufacturer's guidance.
- 2
Sand the surface
A floor sanding machine takes off the laitance across the whole area, including edges and corners.
- 3
Extract the dust
The dust is extracted as the machine works, leaving a clean, open surface.
- 4
Prime and cover
The sanded floor is ready for priming and bonded coverings, once a moisture reading confirms it is dry enough.
Concrete laitance removal
Concrete slabs form laitance as well, and removing it from concrete is a heavier job than sanding a screed. Grinding or shot blasting takes the surface back to sound concrete before coatings, screeds or bonded toppings go down. Our guide to shot blasting, grinding and scabbling before screed explains those methods.
For preparing an existing concrete slab as part of a floor build-up, see our shot blasting and floor grinding service.
Whichever surface is being prepared, the last check before coverings is moisture. See screed moisture testing for how that reading is taken and recorded.
Frequently asked
Need a screed sanded before tiling?
Send the floor area, the screed type and the covering planned. We reply the same working day.