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Key to success

MANAGING damp is absolutely critical. If the situation isn’t taken into consideration, it can seriously threaten the success of the entire flooring installation. Before moisture sensitive flooring is laid on a subfloor base it’s necessary to ensure the floor is constructed to prevent moisture from reaching it from the ground, and that any excess water from construction is dissipated.

Bear in mind there’s a strong possibility that properties dating from before the ‘70s may have been built without a proper dampproof membrane (DPM) under the subfloor itself or that any that were laid are failing or have since failed.

Where serious doubt about the existence of an adequate DPM persists, even where hygrometer readings are 75% relative humidity, then the installation of a well-proven, fluid-applied surface DPM is definitely needed.

Managing excess moisture
We look to two sources where moisture can be found in a building that’s watertight. First, newbuild projects can have moisture related to the construction process contained in the newly installed subfloor.

The other scenario is where there’s no DPM in the subfloor construction or it’s deemed ineffective. This may be owing to it having degraded or expired over time. This situation is usually encountered in older buildings. In existing buildings, it will be the ground floor which will be affected by excess moisture.

In the case of moisture on a newbuild project, there’s a chance excess moisture can also affect the building’s upper floors as well as the ground floor.

Investigations are needed beforehand to establish the situation. This can be done by taking moisture readings as a starting point. There are various methods of testing and manufacturers can advise on the best way to achieve an accurate result.

Once readings have been taken, a decision can be made on what the next steps should be. Where it’s found readings are over 75% relative humidity, then the question can be asked – does the subfloor need an epoxy surface DPM or moisture vapour suppressant?

Traditionally, an epoxy surface DPM, has been used where readings are up to 97.9% relative humidity (theoretically 99.9%).

Before this can be applied it’s vital the subfloor is surface dry, even, and contaminant-free. If the surface isn’t even, pre-smoothing of the subfloor is recommended. This will achieve two things, one, the effectiveness of the surface DPM and two, the correct coverage rate of the surface DPM.

If the above is achieved, the epoxy DPM can be applied directly to the subfloor followed by a primer and then the smoothing compound. The selected floorcovering is then adhered with a suitable flooring adhesive.

It’s worth noting some smoothing compounds can be applied directly to the DPM without the requirement of a primer, however, we’d strongly advise installers to always contact the manufacturer for further guidance on this.

Newbuild considerations
When readings are up to 95% relative humidity on a newbuild project, and there’s an effective DPM installed under the subfloor, a moisture vapour suppressant can be used. Once the subfloor is surface dry, even, and contaminant-free, two coats of a product such as TREMCO ES600 should be applied. When the first coat is fully cured, a second coat is applied at right angles to the first and allowed to dry.

When the second coat is fully cured (usually one hour), a suitable smoothing compound should be applied, followed by the recommended adhesive for the floorcovering, completing the project.

Prime position
The next stage in the installation process to consider is primers. Dry substrates may vary in porosity and require priming to prevent any pin-holing from occurring. Self-levelling floor finishes will adhere well on their own, but a primer can still be essential to stop this. This is an important consideration, as otherwise air in the substrate may rise through the self-leveller and cause air bubbles.

A screed or mortar topping will need a primer to ensure a good bond with the substrate, the exception being some water-based polyurethane screeds, which can be applied to cementitious substrates (concrete or screed) without a primer dependent on the condition of the substrate. However as a ‘belt-and-braces’ approach we recommend always using as if things fail then this can be far more costly than not using a primer.

Products such as Isocrete Primer, an acrylic, emulsion-based primer for Isocrete cement-based self-levelling screeds, can be used to prime concrete and screed subfloors, as well as impermeable surfaces, prior to the screed application.

It improves adhesion to the substrate, reduces surface absorbency and prevents air bubbles migrating to the surface.

This article is just a starting point to discuss key pointers around the subject area. For more detailed information and best practice, the British Standards, BS8203:2017 Code of Practice for the Installation of Resilient Floor Coverings is an excellent reference.
Tarjinder Singh is technical services manager at Construction Products Group (UK) – manufacturers of Flowcrete and Tremco flooring

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