Proper Filed Installation & a Supported Tank Bottom - 9/14/2012 - Design Tanks Blog

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Proper Filed Installation & a Supported Tank Bottom

When installing a fiberglass tank on a concrete pad, it is critical to ensure the bottom of the tank is fully supported.  Special attention must be given to the bottom edge of the tank.  It must be in contact with the concrete pad.  Failure to ensure this may result in tank failure.  A combination of irregularities in the concrete pad and in the tank bottom can contribute to unacceptable gaps around the tank perimeter.  However, if you follow these simple steps as defined in our O&M (Operations and Maintenance) Manual, you can rest assured that your fiberglass tank will perform to your specifications for years to come.


  1. Take a 1/8” thick piece of wood or plastic and slide it under the tank to determine if any excessive gaps between the tank bottom and the ground exist.
  2. If a gap greater than 1/8” is discovered, mark the ground at each end of the gap.  This area will need to be filled in.
  3. Fill the marked gaps with multiple layers of 30 pound roofing felt.  Prepare to fill the gaps by cutting a number of pieces of roofing felt.  The length of each piece will depend on the length of the gap.  Slide each piece of roofing felt under the tank, butting the ends of each piece up to each adjacent piece until resistance is met.
  4. Repeat Step 3 so there are multiple layers of roofing felt in the gap until it meets the tank bottom.  Remember to overlap the seams of each layer below it so that a “step” is not created causing an uneven leveling of the tank.


After all gaps have been shimmed and the tank bottom is fully supported, you can continue with the installation process and know you will have a fiberglass tank that will serve your storage needs for many, many years.