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RE: Inverted Key vs Starter Wall

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Mark---upset curb is more reliable than key and waterstop v/v watertight
construction. The trick is to "hang" the forms from outside the base
placement. The downset key does conflict with mat top steel. We have had a
lot of trouble with multi-cell tanks on a common mat because there is no
good way to hang the forms so far out over a pour. We have tried using rod
pins into the subgrade with gaskets (like a wall form tie fot the tanks) but
they seem to be wobbly. We are still trying to find an efficient way to do
it......I like the demo isea, try to work with the contarctor....

Content-Transfer-Encoding: quoted-printable

I have used both. We use to use the inverted key method, but I = definitely
prefer the curb method since I think it is more foolproof. I = would insist
that if he wants to use the inverted key that he set up a = demo to show he
can do it correctly before I would approve that method. = It is difficult to
do properly! You might ask him how he plans to fix it = when it leaks. =20
Jim K.

-----Original Message-----
From: Mark Urback, P.E. [mailto:murback(--nospam--at)]
Sent: Friday, March 31, 2006 11:30 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?


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