Q: Magnesium-oxide board (ExtremeGreen board) seems to be a ideal building material, but Wikipedia and other sources say it has a problem of attracting condensation due to its salt content. Can you offer any advice? — Keith B.
A: Magnesium-oxide building products – sheathing, wallboard, siding, and other products such as SIPs – are very new in the U.S. so there is little data on real-world performance, at least in the U.S. Most of the material is manufactured in China, where magnesium oxide is readily available.
The product is cast as a cement mixture made from magnesium oxide, magnesium chloride (a type of salt), perlite, and other compounds, and formed into sheets. The main U.S. supplier, ExtremeGreen Building Products, adds wood fiber to the mix.
Suppliers of the product claim that it is an environmentally friendly, inorganic material that is strong, dimensionally stable, fireproof, waterproof, and impervious to insect damage and moisture problems, such as mold, rot, swelling, or warping. All in all, it sounds like a miracle product.
However, I would proceed with caution before choosing this product for your construction project. Few, if any, miracle building products have lived up to their initial hype.
One country that embraced magnesium-oxide board is Denmark. Starting around 2010, it was widely used as a substitute for drywall in public housing and private homes, and as an exterior sheathing in commercial buildings. About five years later, widespread failures occurred, including “weeping” of saltwater, corrosion of fasteners, and mold growth.
Apparently, the boards can absorb moisture from the air during periods of high humidity and, later, release the moisture as condensed water high in dissolved salts. The leaking salt water leads to accelerated corrosion of metal fasteners and fittings. Also the high moisture levels caused mold growth on some projects.
While some building products can resist mold growth, I’ve seen plenty of mold grow on mold-resistant caulks, plastics, and even window glass. Cement boards may not feed the mold like the paper facing in drywall, but given the right conditions, mold will grow almost anywhere.
Whether the Danish problems were unique to specific products, installation details, or climate conditions is unclear. Different magnesium-oxide building products vary in their composition, additives, density, and finishes. And the manufacturing quality of Chinese products can be highly variable.
While the ExtremeGreen products comply with many ASTM standards, I would still proceed with caution. Contractors report that the material is somewhat easier to cut, drill, and nail or screw than fiber-cement, its closest relative in the US building market. That’s a good thing. But it’s still too soon to tell how it will perform long-term.
You can read about the Danish problems at these links:
Denmark Drywall Failures Magnesium-Oxide Moisture Problems
Please add your comments if you’ve had any hands-on experience with magnesium-oxide building products. — Steve Bliss, Editor, BuildingAdvisor.com
Isabelle says
Magnesium-Oxide Wallboard Failing in Canada
We’ve had the same issue on our home in Montreal, Canada. We used magnesium boards in our inside walls and after full plaster and paint… cracks everywhere. Plus the fasteners are rusting… we’re thinking about dealing with the issue by putting wall paper everywhere but worry about even that peeling off…
Mike Sales says
You mentioned fastener rusting. Is the MGO used in replacement of dry wall or is as a structural component? I hope not structural as mine is. My house is MGO SIP’s [structural insulated panels]. and fasteners are rusting, walls cracking, and some sweating. Three engineers failed my house now have been fighting insurance for few years. The engineers want me out this summer over structural concerns. I hope you are not to this extreme.
I’m located in Alberta, BC, and know of 6 houses that are failing structurally. and more to come.
Christine says
Mike, do you know what type of MgO Board you have? Is it Magnesium Oxysulfate? Or Magnesium oxychloride?
Kate W. says
Magnesium-Oxide Wallboard Failure
Your site had a question about Magnesium Oxide boards back in 2016 following the problems experienced when used on external facias in Denmark, but do you know of any experience like ours, where these boards have been used on interior walls?
We live in the UK and have a new build, closed panel, timber frame house using Magnesium Oxide boards on all internal walls, completed in 2017. Soon after moving in, cracks appeared around all the boards and, despite using the recommended primer, large areas of plaster de-bonded and have burst off the walls (see photo). A structural survey found that the Magnesium boards had bowed but that this was not due to any movement of the timber frame. The ceilings are made from plasterboard and are still perfect.
At present at least three of the major build insurers (NHBC, LABC, Premier Guarantee) will not insure buildings which use Magnesium Oxide boards – there is a court case ongoing which makes it impossible to discover how widespread our problem might be. Are you aware of problems with interior uses of Magnesium boards like this, on your side of the Atlantic? We have been trying to get answers and compensation for three years.
Thanks for reading this, and so grateful for any information you can offer.
buildingadvisor says
The material is still not widely used in the US. However, one major US manufacturer, Huber Engineered Woods, now offers a magnesium oxide panel called Exacor for use as a flooring underlayment in multifamily housing, claiming that it offers better sound absorption and fireproofing than competing materials. This would go under the carpeting or other finished flooring.
As mentioned in the article, most MgO panels are made with magnesium chloride, which tends to absorb moisture from the air causing problems with mold and corrosion of metals. Cracking has also been noted by some authors, who recommend spacing the boards and filling the gap with sealant – not a practical option for finished wallboard. It doesn’t surprise me that delamination of plaster would occur with this material.
There are a lot of variations in material quality and composition from one manufacturer to another. The vast majority use magnesium oxide, which is cheap and plentiful in China where much of the material is made. However, some panels are made with other magnesium compounds (magnesium sulfate or magnesium phosphate) which are more expensive but have fewer problems.
Sebastian Tevel says
I have read an article on these materials on another blog and the author claimed that Huber Exacor is actually Extreme Green board, which apparently is one of the best on the market. Huber either bought the Chinese company or made a licensing agreement.
I was researching these “alternative materials” and so far it seems that the best solution for those who want a non-combustible subflooring (like me) is cement board like USG Structocrete. However, it has an MSRP of $4.70/sq.ft. for full truck load orders and it weighs 170 pounds per 4×8-ft. board. Less expensive and lighter than pouring concrete on corrugated steel… yet more expensive than Advantech to buy and to install. Although it is a much better product than Advantech or any OSB subflooring: more durable, more stable, more structurally sound, and non-combustible.
Sebastian Tevel says
Indeed Huber Wood acquired some assets from Extreme Green as per this press release by Huber Wood.
Robin Curtis says
Hi Kate
The pictures of your home confirm there was little adhesion of plaster to whatever the magnesium oxide board composition was. Understanding the composition will be important to establishing an accurate evaluation. Was the product supported by independent testing.
Was the product installed as per the requirements of technical manuals? Was the product at the correct moisture content at time of installation? What plaster type and coating type was involved? Was it approved for use with the product and by whom? What is the humidity and temperature maintained in the home? Did the evaluation extend to removing the magnesium oxide board to evaluate framing an in-wall moisture?
All these questions and more need to be answered when the interior linings are plasterboard. Unfortunately those who evaluate can shift away from the required framework when magnesium oxide is involved. Regards Robin Curtis
Ed Note: Robin Curtis is a director at Health Based Building, a supplier of magnesium-oxide panels and other healthy home building products in New Zealand and Australia.
Edward Gilbert says
The Denmark situation was caused by sub-standard MgO boards. Controlling the manufacturing process is critical to minimize any free ions of MgCl (magnesium chloride). Measuring incoming raw materials and thereby controlling the ratio of MgO & MgCl which bonds to form the cement is a critical step in the manufacturing process.
By the way, Magnum Board is the most tested board available in North America and the only board in the world to have an ESR issued by the International Codes Council, UL Listed in USA & Canada plus CCMC approved in Canada.
Viv says
Magnesium-Oxide Table Delaminated
I ordered an outdoor picnic table and benches that were made out of this material – magnesium oxide. I had it 8 months and the top face of the table began peeling – exposing core. I don’t know if they failed to seal it properly or what, but they ended up sending me a whole new set and said I should make sure and protect it and cover it from weather! It’s made for outside use??!