Replies

1. 
   JohnCujie | Feb 04, 2008 07:04am | #1

   I am not familiar with the Hardie product you mention, but I do know that Hardie Plank alone does not get a class A fire rating. It requires an assembly with 5/8 fire rock.

   John

1. 
   DanH | Feb 04, 2008 07:54am | #2

   I suspect that the problem is that the plank has seams. A hot fire could cause the seams to open up, allowing the heat/flames through.Likely a face nailed assembly would test better than a blind nailed assembly.
   If your view never changes you're following the wrong leader

2. 
   caseyr | Feb 04, 2008 07:55am | #3

   http://www.jameshardie.com/homeowner/fire_faq.shtml
   http://www.jameshardie.com/homeowner/fire_technical.shtml

1. 
   DanH | Feb 04, 2008 04:41pm | #4

   Yeah, gypsum wallboard has the advantage of a very high water content, though I'm guessing Hardi is no slouch in that department.
   If your view never changes you're following the wrong leader

3. 
   renosteinke | Feb 04, 2008 05:12pm | #5

   I doubt it.

   Gypsum owes it's amazing fire performance to it's unique crystal structure, one that traps two water molecules inside it.
   You can see the effect of this if you set a piece of drywall on a stove. You'll actually see a wet spot, as the first water molecule is boiled out of the crystal, at around 250F. Then, much later and at a much higher temperature, you will see steam escape as the second water molecule is cooked free.

   Cement, mortar, etc. does not have this trait. I think there is only one water molecule trapped within.
   Masonry does have one advantage over gypsum; it seems to retain it's mechanical strength after losing that water molecule ... unlike gypsum, which turns into talcum powder.