Floor primers can be an overlooked part of floor preparation, but should be considered an essential part of any installation. If a primer for self-levelling compound isn’t used, your floor could be subject to surface imperfections, including pinholing, which could lead to costly failures further down the line.
By choosing to use a floor primer, you will enhance the bond between the self-levelling compound and the subfloor, and create a barrier to stop air escaping, which means the self-levelling compound can cure correctly.
Why do I need a primer for self-levelling compound?
Most subfloors will benefit from the application of a floor primer to reduce the risk of surface imperfections, such as pinholing.
Pinholes are tiny holes that appear on the surface of a self-levelling compound, particularly when applying to absorbent substrates, such as sand and cement screeds.
Absorbent substrates contain air, which will try to rise upwards when a self-levelling compound is applied and the liquid moves into pores in the substrate. The air is displaced from the porous substrate and will appear as air bubbles in the wet compound.
On very absorbent substrates, or substrates that have been insufficiently primed, there is a risk that the bubbles will remain and form pinholes in the hardened surface due to the “suction” from the substrate.
Besides affecting the appearance of the self-levelling compound, pinholing can also compromise the structural integrity of the floor, which can lead to costly failures.
What does floor primer do?
A floor primer will address any shortcoming in a substrate's porosity, helping to maximise a self-levelling compound’s flow and strength development, and minimise the formation of pinholes.
When applied undiluted, a floor primer also acts as a bonding agent on non-porous surfaces - such as power floated concrete, ceramic tiles, quarry tiles, rigid metal, terrazzo, asphalt and surface membranes – which can greatly improve the adhesion of self-levelling compounds to subfloors.
Everything you need to know when choosing a primer for self-levelling compound
Now that you know why a floor primer is an important part of subfloor preparation, here we look at some of the frequently asked questions when it comes to applying a floor primer.
You can test the substrate's porosity with a water-drop test. Pour a small amount of water onto the subfloor. The longer it takes for the floor to absorb the water droplet, the less porous the floor.
The level of absorbency will determine the primer to be used and whether it should be used diluted or undiluted.
Yes, you can. For a fast-track installation that allows you to install new floor coverings in as little as 4 hours, we offer the following system:
Bostik Cempolatex Moisture Suppressant
A ready-to-use, water based, single part surface membrane for cementitious floors. Two coats will provide protection up to 95% RH and the container is resealable and reusable.
Bostik Cempolatex Rapid 30
A high strength, quick-drying self-levelling compound with a walk on time of just 30 minutes. It will smooth sound, uneven surfaces prior to the laying of decorative floor coverings. It is also suitable for use with underfloor heating. Accepts loose lay floor coverings and bonded tiles from 45 minutes, accepts other bonded floor coverings from 3 hours.
Watch our video for our top tips for a fast-track flooring installation.
You will need to assess how porous your subfloor is to determine how much floor primer you will need.
Floor primer can be used in its undiluted form on any non-porous subfloor, but on more porous substrates, it should be diluted in a ratio of 1:2 with clean water.
A 2.5L unit of floor primer will provide approximate coverage of 37.5-50m² in undiluted form, and 60-75m² when diluted.
The drying time of floor primers varies depending on the primer, how absorbent the subfloor is, and the ambient temperature and humidity. However, it will generally dry within one hour under good drying conditions. Your primer should feel dry and tack-free to touch before applying a self-levelling compound.
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