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RE: Grouting or fiberboard between steel tank bottoms and concrete foundations

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Sitting the tank on a concrete slab  with a slope to drain off water works
fine.  Problems occur when water is allowed to settle under the tank bottom.
For small tanks, be sure to add a vapor barrier under the slab.  Large tanks
usually do not have the vapor barrier therefore the tar paper or felt paper
is needed.  Also, tanks noted in API650 and AWWA D100 are for OUTSIDE use
and do not consider the benefit of indoor protection.

The tolerance you note seem ok for the slab.  If you use the equations for
settlement in API650 you will find the levelness a problem but small tanks
work well outside those limits.  I have seem more problems where the grout
prevented adequate drainage rather than tanks having problems with unlevel

Ron Hill

-----Original Message-----
From: Ed Marshall [mailto:elmarshall(--nospam--at)]
Sent: Tuesday, November 17, 1998 3:17 PM
To: seaint(--nospam--at)
Subject: Grouting or fiberboard between steel tank bottoms and concrete

A question about the interface between a concrete slab foundation (as
opposed to a ringwall foundation) and the bottom of a small to medium
diameter flat bottom industrial steel tanks.  I'm thinking of tanks whose
heights are not much more than their diameters and no more than, say, 20
feet tall.

Many standard references, such as AWWA D100, speak of providing a 1/2" layer
of asphalt saturated fiberboard (with the concrete finished to +/- 1/8"
tolerance in 30 feet circumferential length under the tank perimeter, etc),
a 1" sand cushion, or 1" minimum of grout.  I have also seen details that
call for a couple layers of asphalt saturated felt to be placed between the
concrete and the tank bottom.

However, it seems that many tanks are simply placed directly on the concrete
slab foundation finished to the 1/8" +/- tolerance.  What  practice have you
seen?  Anyone experience any problems one way or the other?

> Ed Marshall
Simons Engineering
> Atlanta, GA