F_BALL_SUBFLOOR_PREP_BROCHURE-Jan-26 - Flipbook - Page 6
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Subfloor Preparation Guide | All aspects of subfloor preparation and floor covering installation
LAITANCE
Laitance is often present on new concrete bases, sand/cement and
calcium sulphate screeds and should always be removed. Laitance is
formed from a mixture of water, cement and the fine particles of the
screed or concrete brought to the surface when placing and trowelling.
As the concrete or screed cures this mixture dries to form a crust or
thin layer (known as laitance) on the surface.
The wetter the mix, and the more it is worked or trowelled, the thicker and usually weaker the
laitance will be. The thickness of laitance may vary from, in the best cases, barely measurable to the worst examples, 6mm or more. Scoring the surface with a steel edge (i.e. a screwdriver)
until the main aggregate in the mix is reached will determine the thickness of the laitance.
Laitance is a friable and weak layer, and can either delaminate or be subject to impact damage,
or may go to dust when abraded by traffic. Therefore, to ensure the new floor surface and
smoothing compound are able to fully bond, the floor needs first to be mechanically prepared to
expose the aggregate in the concrete/screed base. The heavier the floor traffic, and the greater
the temperature fluctuations that the floor area is subjected to, the more important laitance
removal is. If not removed, laitance is a major cause of failure within concrete/screeded floors
and may lead to failure of the surface treatment, smoothing compound or floor covering. Unless
it has been removed by previous surface preparation techniques, laitance may still be present
on old concrete and screeded floors. Removal is vitally important.
Certain propriety brands of screed are formulated not to have laitance present. Should a
desiccated surface through poor site conditions/placement be identified on the surface of
such screeds then the supplies should be referenced for advice about the complete removal
and loose broken material that cannot be adhered to.
To ensure the new floor surface and smoothing
compound are able to fully bond, the floor needs
first to be mechanically prepared to expose the
aggregate in the concrete/screed base.
