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Re: control joints in grouted cmu walls

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Paul,

I am typically used to seeing joints at about 20 feet.  Typically going to
30 feet is pushing your luck.  Keep in mind that in most location that
block walls will shrink (and brick will expand).  You can almost treat the
CMU wall like a slab on grade in a rough, vague way.  Both are concrete.
Both will shrink as moisture evaporated.  Typical PCA/ACI recommendations
for slabs on grade will result in joint spacing on the order of about 20
ft.  A CMU wall will be similar.  Also keep in mind that you should have
joint reinforcing at 16 oc (every other course)...but you are probably
already aware of that.  Make sure that you follow the seismic guidelines
for minimum steel since you are zone 4...I am assuming it is per UBC, but
ACI 530 (masonry code) is also pretty specific...again I am sure that you
are aware of this.

The issues with leaving the joints out is cracks in the wall.  If you are
not worried at all about moisture/weather penetration, then this may not
be much of an issue from a performance point of view.  However, I am sure
that the owner would call someone (you) as soon as the cracks appear.  I
can feel some lawyer just salivating at the prospect of getting some
money...

I am used to seeing caulk in the joints (with a backer bar behind the
caulk typically).  You can just do a mortar joint (a break in the running
bond pattern with a continuous joint full height) but that will likely be
the weak point and you will get a crack and the owner will still call you.

Hope that helps,

Scott Maxwell, PE, SE
On Mon, 14 Aug 2000 PFFEI(--nospam--at)aol.com wrote:

> what are the requirements for control joint spacing in a grouted cmu wall?  I 
> found general typical details in the Concrete Masonry Asociation handbook 
> (recommend approximately 50' - 60' spacing), but no reference in code.  What 
> are the issues with leaving the joints out all together? I have a single 
> story Zone 4 "L" shaped building, 50' and 60' long on the end walls, 
> longitudinal wall max length of 120', and 2 sections at the L side are 30' 
> and 90'.  What is a common joint filling material if block is left exposed to 
> view ? (Using split face block)
> Thanks - Paul Franceschi, S.E.
> 
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