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Unread 04-16-2021, 05:56 PM   #15
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Join Date: Jul 2001
Location: Boerne, Texas
Posts: 92,956
Originally Posted by Don
please don’t take my comments/question as not trusting your knowledge or advise.
Don, you needn't apologize for questioning any advice given you by people not known to you who you've met on an Internet site, including this one. We do pride ourselves on giving out sound and correct advice, and when any one of us strays from that path, one or more of us will be quick to point it out. In my particular case, you can count on several people knocking one another down to do so.

You don't need to understand everything in C1325 or/and C1288, you just need to know they're different and the different products tested under those standards behave somewhat differently. The true cement boards (C1325) have no organic materials in their core constructions. The Fiber/Cement boards, as the name implies, do have such material in their core. For most applications you don't care at all about that portion of their construction. For some applications, those involving moisture, exterior installations, and freeze/thaw conditions, you might.

The shower construction methods published in the TCNA Handbook are a good example of where the difference is worthy of consideration. You will not find any discussion in there about sandwiching various CBUs between multiple waterproofing or vapor retarding membranes because that comes under the heading of "why would anyone wanna do that?"

What you've got may or may not cause you any problems. If it does, you'll not likely know for years. Maybe a lot of years.

My opinion; worth price charged.

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