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Moisture controland waterproofing

Many of the problems that occur with tiling are a result of moisture in the subfloor, or failure to protect backgrounds from water ingress. Ardex training and technical support manager Bradley Cutts explains how these issues can be avoided.

It’s always good to remember that tiles, cementitious adhesives and grouts are themselves not waterproof and can be affected by the passage of water from below or from above.

It’s therefore essential that the right protections are put in place through the correct substrate and background protection, to ensure water doesn’t become an issue.

Various factors need to be considered which we will explore further in this article including subfloor drying times, controlling subfloor moisture and damp, and the installation of tanking systems in wet areas.

Subfloor drying times
Research has shown that under ideal conditions, a screed up to 50mm thick will take approximately one day per mm to dry.

For concrete, at least six weeks should be allowed for initial drying shrinkage, sand and cement screeds three week minimum, while anhydrite screeds can vary – typically it is 1mm per day up to 40mm, thereafter two days per mm.

However, it is essential to check with the manufacturer for drying times and any required moisture levels. Correct moisture checks or tests should be carried out before tiling commences.

The commissioning of underfloor heating in certain screeds prior to tiling installation can enhance drying times, as it can the removal of laitance from anhydrite – which is also critical to ensure good bonding.
Our national training and technical support team can assist with free moisture testing to ensure the levels are suitable for the application of levellers or direct tiling.

Damp proof membranes
However, time scales in many projects do not allow for lengthy drying times, so sufficient time is not left for the construction moisture in the subfloor to dry out.

This is where a surface damp proof membrane can come in handy, as they are suitable for the highest measurable levels of moisture content (up to 98% RH in certain backgrounds), cutting down on drying times.

A surface damp proof membrane will protect levellers and tile adhesives against residual construction moisture and continual rising vapour. They can also be used where a structural damp proof membrane is not present or is ineffective.

Don’t overlook the need for DPMs when tiling, as rising moisture can cause staining of the grout, or in worst case scenarios failure of the tiled systems.

Adhering to saturated concrete at lower temperatures or even cementitious heated screeds, ARDEX damp proof membranes offer quick and effective moisture control.

Waterproofing and tanking
While British Standards have always supported waterproofing in commercial wet areas, in 2018 a new clause to BS 5385-1 introduced guidance for waterproofing domestic wet areas.

Under this provision, any domestic showers, bathroom or other wet areas must have a suitable tanking membrane fitted first.

A wet area is considered to be any wetroom, bathroom, shower area, steam room or any other location that is subjected to frequent water contact.

Because they are water-resistant and not waterproof, over time, water will be absorbed from above through the grout joints and adhesive bed and into the underlaying substrates.

If the substrates aren’t protected with an appropriate tanking system at the right thickness, this can lead to damp and mould issues.

Of course, the longer this goes on, the worse the damage will get, and ultimately this can lead to tiles debonding or failure. Water damage and ingress can even spread to adjoining rooms or even adjacent properties.

So the question should be, do you want to run the risk of failures and potentially being liable for any damage, or just spend a few extra pounds on a quality tanking system – such as those available from the ARDEX Group UK.

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