Sometimes perceived as unnecessary, costly or
time-consuming, priming is actually an essential part of the effective
preparation of a subfloor. Stephen Boulton, technical service manager at F.
Ball and Co. Ltd., examines the advantages of priming and provides advice on
how to select the most appropriate product.
When it comes to preparing a subfloor for the installation
of a floorcovering, priming can often be overlooked. Primarily designed to
improve the bond performance between the substrate and the subsequent
preparation material to be applied, for example a smoothing underlayment,
primers can also reduce the incidence of surface defects. Although primers
cannot be used to correct poor quality substrates or as a stand-alone surface
preparation system, they can reduce the risk of ‘cratering’ and pin holing
which can be caused by air that has been trapped when cementitious or
resin-based smoothing compounds are applied onto porous surfaces.
In addition to reducing the risk of surface imperfections,
priming enhances the application characteristics of flooring installation
products. Sealing the porous surface of a subfloor reduces the surface tension
and improves, for example, the flow properties of the subsequent materials
being applied. Where cement-based smoothing underlayments are used, priming
helps to reduce water loss into the substrate, retaining a wet edge longer for
ease of installation, as well as adding to the strength and shrinkage
characteristics of the underlayment material. Furthermore, reducing the amount
of water lost through the use of a primer also helps to maintain the open time
of flooring adhesives when they are applied directly to porous screeds and
concrete surfaces.
A prime selection
When selecting the most appropriate primer for a project, it
is important to take into account both the type of screed that will be applied,
as well as the condition of the subfloor surface. Polymer emulsion primers,
such as acrylic systems, are recommended for use with cementitious screeds.
Specially developed neoprene primers can be used for a broader range of
absorbent and non-absorbent applications. For resin-based screeds, two-pack
epoxy, or polyurethane primers provide the best solution.
Selecting an inappropriate primer, or failing to install it
correctly, can lead to failure of the floor once it is in use. Cracking or
delamination of the underlayment material due to insufficient, or incorrect
priming requires remedial work or, in the worse case, an expensive ‘rip out’.
Effective preparation
To maximise the performance of primers, they must be applied
correctly and in a suitable concentration. When it comes to applying the
primer, the subfloor surface must be smooth, clean and dry, as well as incorporating
an effective damp proof membrane. Furthermore, the temperature of the surface
must be assessed when the primer is applied to the subfloor to ensure the
product can be applied correctly.
Paint rollers and brushes are the conventional primer
application methods. However, water-based primers, such as acrylics, are now
available as sprayable systems, enabling faster installation times to be
achieved. Selecting priming systems which are pigmented enables the user to
more easily achieve uniform coverage, helping to ensure the long-term
durability of a floor. In addition, it is important to consult manufacturers’
guides regarding installation methods since some priming products require the
subsequent product to be applied while the primer remains tacky, whereas other
types of system need the primer to be dry before the installation can proceed
further.
Where necessary, contractors should also choose primers that
are compatible with underfloor heating systems. Prior to the installation of
primers, underfloor heating systems must be switched off 48 hours before,
during and after application to enable natural drying of the product.
As well as providing performance and installation benefits
for absorbent and non absorbent subfloors, priming can also enable a screed to
be applied over some contaminated surfaces, such as minimal hard, stable
adhesive residues. However, contractors should be cautious when priming
surfaces that may contain silicon-based treatments as this can inhibit bond
formation. For advice on selecting the most appropriate primer system for
contaminated subfloors, contractors should contact the manufacturer.
To ensure the longevity of a flooring installation, priming
should form an essential part of the subfloor preparation. Quick and easy to apply,
primers improve bond strength and reduce the risk of pin holing. Careful
evaluation of the subfloor composition and condition will help contractors to
select the most appropriate priming system for a project, maximising the
appearance and performance of the floor.
Contact F. Ball and Co. Ltd., on 01538 361 633 or visit
www.f-ball.co.uk
