Main finishing options for Magnesium Oxide boards

Another question came in yesterday about the finishing of Magnesium Oxide Boards in case of exterior walling.

The most common exterior surface finishes are: Paint, Plaster and Tiles.

Before you start applying the finishing material:

When the MgO boards are fitted, the boards should not be exposed to the weather for a long period of time. Both heavy rains or high dryness will have their negative effects on shrinkage or expansion of the boards. These will cause cracks later when the finishing material is applied.
The MgO boards should also be clean and dry before starting finishing.
Small damages to the MgO boards should be removed or repaired.

Paint

Paint can be applied easily to the MgO boards. For exterior use, the boards should be primed with 1 or 2 coats of Plaster/Masonry Primer before coating with exterior quality paint. The primer works here as a sealant and water repellent that protects the ‘open’ structure of Magnesium Oxide Board.

Plaster

Cement plaster can be applied to the surface of the MgO boards. All joints between the Boards must be meshed with Fibre Mesh (preferably 4mm x 4mm) or wire scrim prior to applying the cement plaster coat.
After plastering, a sealant primer should protect the Plaster.

Tiles

Tiles may also be applied to the surface of the MgO boards. In this case it is recommended to roughen up the surface of the Board and put a suitable bonding agent (glue) on it before tiling. The amount of Glue has to be affluent.

When the tiles are applied for walls higher than 10 feet, these tiles should not be bigger than 1,3 Square Feet and thicker than 12mm.

Fungus and Magnesium Oxide boards: happy marriage?

Last week we were called by an Indian architect, who wanted to use SINH™ boards to cover air-condition piping’s. He wanted to know if Magnesium Oxide Boards would host or stimulate the growth of fungi in his construction.

As our company has not yet conducted a test to cover this issue, I started to search the internet for answers. First of all, you should know that there are thousands of species of fungi. Most of them are unharmful, only few of them cause illness and allergies.

Like Duane Craig (2009), who is a blogger for The Construction Informer, wrote in 2009: “Most of the time even though mold is present in our buildings it isn’t actively growing to the extent we can see it with the unaided eye. Then too, mold growth is greatly affected by humidity and since many of our buildings are air conditioned, or use dehumidifiers, the opportunity for mold growth is diminished.”

I also came across an article of Pamela Hargrove (2004): Testing for Fungal Growth in Building Products: a collaborative Effort. This article shows main tests available and developed in cooperation with ASTM, the American Society for Testing and Materials.

To summarize, there are 3 main test methods for the panel products industry available:

1. ASTM G21 – is a method used to test synthetic polymers including poly(vinyl chloride) and plastics.

2. ASTM D 3273 – is a standard Test Method for Resistance to Growth of Mold on the Surface of Interior Coatings in an Environmental Chamber. This standard is for fungal growth in soil, contained in the humidified environmental chamber. Air circulation within the environmental chamber circulates the fungal spores in the chamber to the vertically suspended samples four inches over the soil. Weekly photographic images of each sample are emailed to customers so they can follow the progress of the testing.

3. ASTM D6329-98(2008)– Standard Guide for Developing Methodology for Evaluating the Ability of Indoor Materials to Support Microbial Growth Using Static Environmental Chambers. The test is designed to run for 12 weeks, four times longer than ASTM D3273. The quantitative assessment here is a count of the number of colony-forming units (CFUs) taken from samples collected during weeks 1, 6 and 12, and compared against the baseline level of CFUs at the start of the test.

Some other standards (not limitative) that have been published for testing of materials for resistance to fungi are:

  • MIL-STD 810E – Method 508.4 – Determines whether fungus will grow on a device exposed to warm, moistured air in the presence of fungus spores. The MIL-STD 810 involves spraying the test items with a composite of fungal spores and supporting the test items in the environmental chamber for 28 days.
  • ASTM C 1338 – Fungi Resistance of Insulation Materials and Facings
  • ISO 16869 – Assessment of the Effectiveness of Fungistatic Compounds in Plastics Formulations

To address the need for uncoated building products including gypsum board and cement board, a task group was formed in February 2004. The proposal in 2011 for a new test method ASTM WK32079, (Test Method for Determination of Mold Growth on Building Products designed for Exterior Applications) is one of its results.

In conclusion:

  1. Each test has its own strength and limitations;
  2. There are no special designed test methods dedicated to test fungi resistance of Magnesium Oxide Boards (external & internal applications);
  3. To limit fungi growth best is to manage humidity. To manage humidity, the architect and builder have to pay attention to building design, product choice, good construction practices and proper maintenance;
  4. Characteristics of Magnesium Oxide Boards as a material do not favour the growth of fungi due to its open molecular structure and high permeability to vapour.

 

My answer on the question “Fungus and Magnesium Oxide boards: happy marriage?” would therefore be “NO”.