You see it along walls, between curbs and pedestrian ramps and every 60 feet in your neighborhood sidewalk. The color of expansion can be dark brown, black, white, beige or gray. It is there for good reason. It allows the concrete to grow in hot weather and also acts as a bond breaker, along walls and curbs, reducing the chance of cracking while concrete is shrinking during the first few days.

Most concrete Contractors are still using concrete expansion material from a bygone era. Asphalt impregnated fiber board has been around since long before my time and is still spec’d out in many municipal projects. The antiquated product may fool an inspector but Contractors who have used more modern product never go back.

Even though the fiberboard is there to provide cushion when the concrete expands, it is too rigid to allow much movement. Nomaflex is a firm but much less rigid product that directly replaces fiberboard. The lightweight product is superior in every way. It can be wet set or Spray adhesive can be used to keep it tightly in place. I’ve heard complaints of it floating up but we have never had any trouble with that. Here is a pdf link to check out.

Foam Tech closed cell polyethylene expansion is soft and super flexible. It is best to use a spray adhesive to install it. It is ideal for areas such as corners that jut out into the pour to act as a cushion. As the water leaves the concrete and shrinkage to the center occurs the soft expansion moves with it instead of resisting and causing a crack. I am a huge fan of this product. I have personally used it for more than 20 years and will continue to use it forever.

Take a look: Foamtech PDF

Your Contractor should have a good understanding of why expansion joint is used and how it should be used. Never allow your Contractor to install any type of expansion with nails! This will completely negate the function of the expansion and focus pressure directly onto the nail making cracks much more likely.

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Jon Molden
BST Concrete