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RE: Inverted Key vs Starter Wall

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I have used an inverted key a lot. But never on a tank for the reasons that you mentioned. Of course the contractors would prefer an inverted key, but they will not be in the crosshairs if the tank leaks. Some engineers will use inverted keys on a tank, I won't. It is a serviceability issue and ultimately it is your call.

Harold Sprague

From: "Mark Urback, P.E." <murback(--nospam--at)>
Reply-To: <seaint(--nospam--at)>
To: <seaint(--nospam--at)>
Subject: Inverted Key vs Starter Wall
Date: Fri, 31 Mar 2006 11:29:50 -0600

Our standard detail for a wastewater tank wall is to provide a starter
wall on the slab with a key and PVC waterstop in the joint.  The
contractor has proposed an inverted key using 1x4 form attached to the
inside of the vertical rebar with a PVC waterstop at the top of the key.
My concern with this method is that the base of the key is at the
slab/wall interface.  If the key were to crack at the slab (where the
bottom of the joint is located), there would be a potential water path
because the water stop would be above the crack.  Has anyone used the
inverted key and have there been any problems?

Thank you,

Mark L. Urback, PE

Assistant Manager

Public Infrastructure Services

Edminster, Hinshaw, Russ and Associates

10555 Westoffice Drive

Houston, Texas  77042

713-784-4500 ofc

713-784-4577 fax

713-202-1579 cell

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