The Importance of Compression

Earlier this year I wrote a blog titled "why is my concrete tank leaking?"  In that blog I mentioned that volume was one of the important characteristics of a quality seal with a compression sealant.  The volume of sealant needs to be the minimum amount of sealant needed to fill the joint and create a watertight seal.  The volume of sealant does not change as the sealant is compressed.  Actually, the sealant only changes shape.

As the photo to the left shows, the sealant begins as a shape that typically represents a square.  The force of the lid will be applied to the top surface of the sealant, causing the sealant to flow laterally.  As the sealant begins to compress, the surface area making contact with the lid increases.

The photo to the right shows the sealant compressed 25%; the remaining gap is 75% of the original height of the sealant.  The width of the sealant has increased 28%.  The for applied by the lid is now distributed over a larger area.

Concrete Sealants, Inc. advises 50% as the minimum amount of compression necessary to produce a watertight seal.  More compression is optimal, but less than this will result in a reduction in the effectiveness of the seal.  Also at this point, the sealant has now increased in width 100%, and the surface area has also doubled.

Somewhere around 75% - 85% compression, the sealant will have reached the maximum amount of compression that will typically occur.  And, while it is possible to exert enough force to compress the sealant, the resistance per square inch continues to increase, as does the amount of surface area where the force is applied.  At 75% compression, the width has increased nearly 400%.
This is a very basic concept of the effect of compression.  Sometimes a precaster will want a wide sealant that is short.  This is not the best option to obtain a watertight seal.  If the sealant is already wide, then obtaining 50% compression will be very difficult since the force will be distributed over a larger area to begin with.  We call this the "snow shoe effect", referring to the ability for someone to walk on snow with special shoes that distribute the weight over a larger area.  Taller sealants usually allow for more compression, and the result is a better seal.
For more information on sealants, sealant sizes, and the effect of compression in obtaining a watertight seal, contact Concrete Sealants, Inc. at 800-332-7325.  A sales representative will be happy to assist you in finding the right sealant size for your application.