What is Liquid Screed Laitance?

You may have heard that removing any laitance from the surface of your dried liquid screed is an important step toward ensuring that you get the best results possible from your newly laid floor, but you may still be wondering what laitance really is, and what the possible consequences of leaving it on your freshly poured screed are.

It is important to bear in mind that laitance removal should not be skipped, and that your floor screeding contractors will be able to carry out this important step shortly after your screeding has been poured. Read more about what laitance really is, why it occurs on new screed flooring, and the problems that can arise when it is not properly removed.

Why Does Laitance Form?

A thin film of laitance naturally occurs during the drying process as fine particles and residue are ‘pushed’ up toward the surface of the screeding.
This is most commonly caused by an excess of water in the liquid screed mixture, heavy foot traffic, or leaving the screed to dry in an environment that is damp, or not temperature controlled. It is a very normal consequence of pouring concrete or liquid screed, which is why laitance removal is a crucial step in laying floors.

What Does Laitance Look Like?

The severity and thickness of laitance varies greatly. It can appear as a fine, loose powder or — in the worst cases — a surface layer several millimetres thick, although one of the greatest benefits of using a calcium sulphate based liquid screed is that laitance is often minimal.
The simplest way of seeing laitance for yourself is to gently scratch the surface of your liquid screed floor with a screwdriver, around a week to ten days after it has been poured. Any loose dust particles will indicate that laitance removal must be carried out before your floor coverings are laid.

Why is it Important to Remove Laitance?

Laitance forms a very weak layer on top of your flooring, far less durable than the liquid screed beneath it. Overtime, any remaining laitance will weaken under foot traffic, which is likely to cause cracks and delamination — both of which are very costly problems to put right.
After pouring your liquid screed, your floor screeding contractors will set aside time a week or so later to return and perform the vital step of laitance removal. There are a number of different techniques used for this process, depending on the size and shape of the surface area in need of work, such as shot blasting, mechanical planing, scrabbling and abrading.
When your site is following a tight schedule, it can be tempting to skip this final step and lay your floor coverings without removing laitance from the screeding. While this is sure to save you some time in the short term, it will put the site at risk of future faults and damage that are much more difficult — and time consuming — to fix.