Back Prime Fiber Cement Siding?

Posted by tbasc@bellsouth.net on July 22, 2008, 12:13 pm

I'm receiving conflicting 'information' on painting fiber cement
siding.
I have info from tech rep & web site each of two manufacturers.
The question is whether or not to back prime fiber cement siding.
Has anyone any experience?

Posted by RicodJour on July 22, 2008, 12:43 pm

wrote:
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I've never done it. I just seal the cut edges. Then again I don't
have several decades of experience with the stuff, so I can't say if
there will be a long term problem if not back primes. I'd tend to
doubt it though - back priming developed to keep wood siding from
absorbing moisture, but fiber cement is far more stable, absorbs less
moisture from the atmosphere, and I've taken down wood siding of all
types that was not back primed and had no problems even though the
wood was fifty years old or more. I'd tend to think that completely
sealing the piece is unrealistic and would tend to trap moisture.
Fiber cement siding drying out from the back would probably keep the
paint from blowing off of the front.

Posted by Craig M on July 22, 2008, 4:24 pm

Dont know what type siding your using, but Hardie is already primed, I think
it's primed on both sides, I have installed it on my house, even if not,
dont let the exposed side stay un-painted too long, or you will have to
prime it, use good paint and it will last a long time, even cheap paint will
do well on Hardie.
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Posted by Dioclese on July 23, 2008, 10:50 am

Can only detail my dealing with James Hardie horizontal lap siding. Retail
version, typically gotten at local big box store, is primed on the facing
side. Unprimed on the backside. Details at their website don't mention
priming the backside at all. They are very, very specific on the type of
paint to use. This I experienced while building my own stand-alone garage.
The concrete siding the builder used on my home was not James Hardie brand.
They had to prime it all before painting it. Was primed after the siding
was installed.
Concrete siding wicks water, makes it soft. That's why they (James Hardie)
require a minimum distance from the soil line. If installed, primed, and
painted properly, there should be adequate enough ventilation to vent any
moisture leakby with horizontal lap siding.
--
Dave

Posted by tbasc@bellsouth.net on July 23, 2008, 8:36 pm

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Thank you all.
Job uses 4x8 sheets with battens.
I'll go without priming or painting the back side.

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