Dispelling the Moisture Myths

With recent reports published in Denmark and Australia sating doubt over the use of Magnesium Oxide (MgO) boards in exterior building applications, John Taylor, Chairman of the Magnesium Oxide Building Board Trade Association (MOBBTA) explains why MgO remains a robust specification.

The Danish and Australian reports have not surprisingly caused some unrest with regard to the use of magnesium oxide building boards in exterior building applications. While there is clearly evidence in other countries of these boards failing a few years post-installation, the subsequent investigation which was undertaken to establish the cause of failure has several shortcomings – most notably in relation to moisture.

Moisture myths

Firstly, the Danish report observes that magnesium oxide boards absorb moisture at higher levels of humidity. The reality is that magnesium oxide boards are no different from other porous boards in this respect and the same would be the case with all common exterior boards such as Portland cement or wood-based boards. Secondly, the report also states that boards break down after exposure to moisture or high levels of relative humidity. Given that many of MOBBTA members’ boards have undergone testing according to the fibre cement boards manufacturing and testing standards – EN 12467 and achieved category A or B performance, this is clearly not the case. This testing protocol means the boards have undergone a minimum of 25 cycles of soak/dry exposure without breaking down. Moreover, while not mentioned in the report, it would be prudent to note that there have been several other instances in Denmark where magnesium oxide based boards were used successfully in the same application. It is therefore proposed that other boards in Denmark were not subject to moisture ingress, which brings into question the importance of quality control within manufacture.

Quality control

– from manufacture to installation Having undertaken a detailed review of the test data and protocol available from the Danish report, it became apparent that the Danish boards had a much higher organic content than MOBBTA members’ boards which would support the high levels of moisture gain which was measured. In contrast, MOBBTA members’ boards contain around 5% wood chip content and when subjected to the same testing protocol as used in the Danish report, were found to exhibit far lower moisture absorption. Moreover, MOBBTA members’ boards showed no mould growth as compared with extensive mould which appeared on the Danish boards.

Moving on to address the concerns raised in the Australian report, the focus shifts away from moisture to corrosion. Crucially, under these circumstances the boards were used as permanent shuttering or formwork elements. While MOBBTA members do not promote the use of magnesium oxide boards in this application, it is important to examine why corrosion may have occurred. Quite simply, corrosion will occur when the boards have not been correctly cured, which leads to the conclusion that quality control during manufacture, both in relation to organic content and curing process, are of utmost importance – and why MOBBTA has been formed to help raise and maintain standards in the industry.

Setting a Quality Mark Standard

In the absence of a harmonised ISO EN or British standard, there is no limit as to how much organic content can be used to produce boards claiming to be magnesium oxide. Striving to introduce a quality standard, MOBBTA members’ boards must contain around 5%, a level which is known not to fail due to moisture ingress.

Further quality assurance with MOBBTA member boards is also being developed through the introduction of manufacturing inspections which will help to ensure curing processes are accurately followed.

Finally, it is known that breather membranes were not used in the Danish installations. MOBBTA members will always advise that a breather membrane should be applied when magnesium oxide boards are used in exterior building applications and that the boards are not approved for permanent shuttering or formwork elements.

As a trade organisation, MOBBTA is focused on creating and maintaining best practice standards in the manufacture and installation of magnesium oxide based building boards. This is crucial in ensuring the industry can continue to benefit from the far-reaching advantages of magnesium oxide boards over other common building board types.

In conclusion, when reviewing the suitability of magnesium oxide based boards for building applications, the market should not be misled by moisture myths. When the technical data behind the Danish and Australian reports is examined in objective detail, the truth becomes very clear. Providing they are manufactured and installed in accordance with MOBBTA guidelines, magnesium oxide based boards remain one of the most robust and highest performing specifications on the market.