Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: Inverted Key vs Starter Wall

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Although I haven't used the inverted keyway myself, my understanding is that it has been used in walls that have adequate thickness such that the keyway width can be designed to resist the shear.  It is also my understanding that some structures have in fact experienced cracks that circumvent the waterstop with inverted keyways where detailing was not adequately designed.  So you have a valid concern.
I typically show a starter wall.  In some cases, I increase the top cover on slab rebar to 4-in and eliminate the starter wall (e.g., where the slab thickness is dictated by other requirements).
I have also sometime used expansive waterstops without a starter wall - usually in small structures such as junction boxes.
William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)

From: Mark Urback, P.E. [mailto:murback(--nospam--at)]
Sent: Friday, March 31, 2006 10:30 AM
To: seaint(--nospam--at)
Subject: Inverted Key vs Starter Wall

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