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Stay ahead of Moisture

Whilst moisture control is a key issue for any building designer, it is especially important in the UAE, where the inter-action of hot humid outdoor air and mechanically cooled interiors creates a recipe for internal, structural and condensation problems. Gyproc’s Technical Development Manager, Jason Hird, examines the part played by wall and ceiling linings in preventing moisture damage in buildings.

Worldwide, an estimated 75% of building failures are caused by water – either as a result of atmospheric moisture penetrating the structure through construction flaws or poor design, or condensation forming within the structure or on internal surfaces due to temperature imbalances. Although rainfall is not a problem here, we have to contend with very high levels of humidity in the external air, compounded by artificially high temperature differentials between the interior and exterior of our buildings due to extreme use of air-conditioning systems, both of which conspire to force moisture into our buildings.

But as well as moisture entering the building from outside, it will be created within a building due to the activities which take place – people breathing, or activities such as bathing or exercising in a gym.

Effect of moisture

Without effective control, moisture can cause a whole host of problems within a building – from ugly staining and mould growth on internal walls and ceilings to deterioration of the building structure itself due to damp and decay caused by hidden ‘interstitial ‘condensation within the external wall and roof structure. This condensation is involved in corrosion of steel components, chemical deterioration of gypsum lining boards, ceiling tiles etc and deterioration of concrete and masonry. Even without the physical damage, it can affect the performance of the external fabric by reducing the thermal effectiveness of insulation and other construction materials.

Perhaps more important, however, is the effect that condensation and mould growth on building components, furnishings and carpets can have on the health of building occupants. Damp, humid atmospheres create ideal breeding grounds for fungi, bacteria and dust mites which promote asthma and lung problems.

Addressing moisture issues

There are a number of ways in which the designer can reduce the likelihood of moisture problems occurring in a building, for instance by incorporating constant fresh air handling systems to reduce the amount of expensive air conditioning needed.

Reducing the opportunities for external warm moist air to penetrate the building through the use of controlled ventilation systems, using airtight construction techniques and vapour barriers in the external wall and roof construction to seal any construction gaps and cracks, and creating positive pressure within the building to reduce moist external air filtration through open doors and windows, will also reduce the amount of moisture penetrating from the outside.

This is not the complete answer, however, as it does not address the other issues such as construction moisture which is gradually released as the building dries out.

One of the most common contributors to construction moisture is the use of poured concrete and blockwork with sand and cement render which continues to release moisture into the building for many months as they dry out.  This can cause damp, decay, mould and bacteria. These issues can be addressed by using appropriate dry construction techniques rather than traditional ‘wet’ trades, such as internal dry partitions and linings, wherever possible.

Internal thermal linings with plasterboard finishes cool or change temperature more quickly than masonry equivalents, so there is less delay in achieving room comfort conditions, and lower risk of condensation as lining responds quickly, changing temperature at a similar rate as the room air.

There may also be instances where, during construction, internal dry lining commences before the building is fully weathertight.  If external environmental conditions are extreme and relative humidity (RH) is continually above 70%, it may be necessary to use moisture resistant (MR) versions of the specified Gyproc plasterboards – i.e. Gyproc Moisture Resistant in place of standard plasterboard, or Gyproc FireStop MR or DuraLine MR in place of the standard grades. This will ensure that the boards do not degrade, bow or sag due to the humidity, especially on ceilings, and will help prevent moisture penetrating the structure until the building is properly closed off.

Lining selection

Gyproc’s range of performance plasterboards make perfect internal linings for any masonry external wall as they quickly adapt to changes in internal room temperature, helping to maintain a constant internal environment.

Further improvements can be achieved using a wall lining system, such as Gyproc GypLyner – a metal frame lining system that can incorporate a separate insulating layer of glass wool, polystyrene or phenolic foam within an adjustable cavity. By choosing different insulants, the lining can be engineered to provide different levels of thermal performance and can minimise condensation risk in each area of the building.

By significantly improving the thermal performance of the outer envelope, less energy is needed to maintain a comfortable and constant indoor environment and the demand for expensive air-conditioning systems is reduced – possibly even leading to smaller air-conditioning installations, all of which helps to further cut condensation risk.

Pay attention to tiled surfaces

Particular attention must be paid to wet rooms and kitchens where traditional tiled finishes can be at risk when surface water penetrates to the underlining board. Problems are often not realised until tiles fall away from the wall surface, by which time the lining is generally saturated and must be replaced – bringing disruption and considerable repair cost.

It is often assumed that expensive tile backer boards or cementitious boards are the only option for tiled applications, but Gyproc Moisture Resistant board has been industry proven for decades, and will provide a much more cost-effective solution.

When applying tiles to Gyproc Moisture Resistant, all that is needed is to use a 15mm thickness board and reduce stud centres to 400mm. This construction is perfectly suitable for most tiled backgrounds, with tile thicknesses up to 12.5mm and a tile weight up to 32kg/m2. Heavier tiles and marble cladding can also be easily accommodated using direct mechanical or batten fixing – further guidance on tiling applications can be found in the Middle East White Book Tiling section.

What is Gyproc Moisture Resistant?

Specially developed for tile backing and high humidity environments, Gyproc Moisture Resistant board is regular plasterboard but with special moisture repelling additives in the core and paper liner, giving it excellent moisture resistance.

The same technology is applied to a range of performance boards so that properties such as impact resistance and fire resistance can be coupled with moisture resistance in a single board. Typical examples include Gyproc FireStop MR, which combines excellent fire resistance with moisture resistance and Gyproc DuraLine MR, the popular high impact lining but with additional moisture resistance properties – ideal for school changing rooms, hospitals, clinics and other similar applications where a range of performance is important.

All Gyproc MR quality boards will provide resistance to moisture up to a certain level, as defined by several international standards, such as ASTM C1396, BS 1230 and EN 520. The general requirement is defined within these standards as the sampled plasterboard having absorbed no more than 5% of water by weight after two hours full immersion in water. Whilst the Gyproc Moisture Resistant plasterboards are not water proof as such and are not suitable for fully exposed external applications or for use as a water barrier, they are perfect for most internal or ‘semi-exposed’ building applications, such as bathrooms , kitchens, wet rooms, semi-exposed soffits, where excess humidity or occasional wetting may be apparent.

The next level

Our innovation and development team is continuously working to develop new and improved products for every area of performance, and moisture resistance is no exception.

They are currently working on a new generation of board that will provide high levels of protection against both moisture and mould growth – making it ideal for a range of damp environments. Based on new technology from the US, the new board achieves the highest possible score for mould resistance against ASTM D3273, as well as meeting GREENGUARDenvironmental standards in key ‘Indoor Air Quality’ and ‘Children and Schools’ categories.

If you would like further details on our moisture resistant range of boards or would like to learn more about our brand new moisture & mould resistant board, or would like to see copies of other articles in this series (covering Fire, Acoustics, Thermal insulation and Impact performance), see our web site www.gyproc.ae or contact our technical department at +971 4 4502300.

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