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RE: New concrete SOG on existing SOG

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Many years ago I investigated a 4 inch warehouse slab which, for a reason I
forget, had been overlain with a 4 inch topping slab. The topping had been
placed directly on the existing slab - no bond breaker and no attempt to

As I recall, the CJ's in the topping were aligned with those in the base
slab. The spacing was probably about 20 ft.

The topping slab had very slightly curled and the topping concrete at the
joints was seriously spalling under the fork lift traffic.

Be sure to take all precautions to avoid a similar problem.

Frank Hartzell

-----Original Message-----
From: Bill Marczewski [mailto:bill(--nospam--at)]
Sent: Tuesday, May 20, 2003 11:34 AM
Subject: New concrete SOG on existing SOG

I've been asked to design a (N) new concrete SOG foundation for a =
pre-eng. Metal building.  The site contains an existing warehouse with
an (E) existing concrete SOG.  The owner wants to raise (E) SOG a total
of 9" via (N) SOG, to be level with an adjacent building.  What are the
lists thoughts on pouring a structural overlay slab on existing, should
any sand layer be present between new and existing slab?  Owner doesn't
particularly want to pour 9" of concrete if something of a compacted
road base between layers could be used.  I'm not familiar with doing
this.  I'll continue my research but would like to hear some of the
rules of thumb for pouring such a slab.  Thank you.

Bill S. Marczewski, P.E.

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