I read the discussion of the mgo board with patient. I am relatively new to mgo board.
The major confusion is mgo board and fibre reinforced mgo board.
mgo base construction in China started with firebricks/bricks for furnaces in early 19 centry and it has been the dominate material since.
The bricks are burned in a way to make it very strong and block the heat from furnace.
With the development of the technology, some of the mgo bricks are made to be thin and about 1/2" thick and gradually leaded into the mgo board.
As mgo boards, at size about 4'x8', with massive production, without the traditional "baking" process, or too expensive to do so, are relataively strong and non-combustible per ASTM E 136, but have two major weakness, they are too brittle and doesn't resistant to water.
As stated by David Mills, when they get wet the Magnesium Chloride can leach out of them which degrades the integrity of the cement. Not to mention that magnesium chloride salts are very corrosive to metal that comes in contact with the salt. In AC 386, the last para, 5.4 it shall not be used in wet areas described in IBC Section 2502 and shall not be used in showers.
Back to mgo board, to increase the strength of traditional mgo boards, fiber reinforced mgo based sheet were developed. And we finally have an AC 386. But AC 386 did not specify what kind of fiber shall be used. And AC 386, failed to set up a industrial stardard other than set up the criteria based on one big company who has a deep pocket, similar to the way as AC 376. (Maybe because AC is not an industry association, but it should set up a AC creteria based on an industry standard not a single product from a company. The industry needs to set a standard for fiber reinforced mgo board.
If any organic fiber, wood, cellulose fibre(pulp) are added to make them structural applicable, ( that is to replace plywood, OSB), the amount of organic fibre added is going to make the penal strong but it will fail ASTM E 136. A number of tests conducted on samples of fibre reinforced mgo board failed ASTM E 136 while still claimed to be non-combustible. Lots fibre reinforce mgo board contains about 20% wood or celluse or fibreglass. This is why we read conflicts of properties of mgo boards.
Most of the mgo board manufactories in China are now fiber cement boards (use celluse fibres) manufacturers as well as they adapted to relatively new product similar to hardie panels.
But neither mgo boards nor fiber cement boards are intended for structural applications-more for sidding or partitioning.
Only CEMENT BONDED PARTICLE BOARD, the last member of the particle board familty, widely used in Europe in the past 80 years, are structural boards to replace OSB and plywood, which is also inflammable, moisture resistant, termite and molds resistant. In UK, CBPB is widely used for almost all buildings.
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