Why Hardiflex (Cement board) can't be used on hot-rolled steel section? 1

[lager]

http://www.jameshardie.co.nz/productfiles/0054864001404956645.pdf

The cement board Hardflex manual says "Sheets must not be fixed directly to drawn steel or hot-rolled steel sections"?

May I know the reason for it? Are there chemical reactions between cement board and hot-rolled steel sections?

But most steel sections are hot rolled.. is it not?

 

[lager]

I think Hardieflex has the thoughts that hot rolled steel has different properties to cold rolled steel.. but then googling. I found out they indeed do! Here:

http://www.eaglesteel.com/download/techdocs/Carbon_Steel_Grades.pdf

Alloy 1018 is the most commonly available of the cold-rolled steels. It has yield strength of 53.7 ksi.

ASTM A36 steel is the most commonly available of the hot-rolled steels. It has has yield strength of 36.3 ksi.

"The hot roll process means that the surface on this steel will be somewhat rough. Note that its yield strength is also significantly less than 1018 - this means that it will bend much more quickly than will 1018."

So Hardieflex has it reverse.. cold formed steel is harder than hot rolled steel given the same thickness!

 

[hokie66]

But it isn't the same thickness. In the context of your problem, hot rolled steel is thick, cold rolled steel is thin.

 

[civeng80]

Fixing hardiflex sheets on steel especially thick steel is something I would just not do regardless of Hardies specs.

Imagine fixing sheeting and drilling holes through a 6mm thick plate. Fix timber battens to steel then fix sheeting using timber fasteners so much easier. Also the timber would be better backing material in case of any movement in the structure.

 

[jwilki]

..... This is a bit of a over complicated thread. Pick up the phone and have a chat to Hardie's is unsure about materials or their fixing.

Hardie's recommendation comes from the fact they specify a 20mm Buildex FibreTek screw for steel up to 0.75mm BMT and a 8g-32mm HardieDrive for steel thickness up to 1.6mm thick... If one wanted to attach to, say a 89x89x3.5 C350 SHS then you would have to nominate an appropriate fastener that would self tap through 6mm of tough fibre-cement sheet and then try and punch through 3.5mm steel (and if they tried to do this is a nominal tek, they would have a lot of frustrated builders)

If you want to know what type of steel it is, hot rolled or cold formed, ask to what steel standard it is. (AS 1163, AS/NSZ 1594, AS/NSZ 1595 & AS/NZS 3678 ARE ALL COLD FORMED STEEL) - your purlins are likely AS1397 G550 grade...or your supplier got their steel from China and should kindly return it back to them...

The fixing pattern you have posted is for a bracing panel... you do not need such a ridged fixing pattern for ceilings

The racking resistance for earthquakes for residential and light commercial construction can be provided by materials such as Hardiebrace... a concrete shear-wall is also pretty rigid and buildings have them in seismic areas too