We are an international development company. We specialize in buildings with large areas of concrete floors. Joints in the floors have become a major problem for us. We have a maintenance company on retainer but the repair patch never lasts. Why do we have to have joints at all? Is there a long lasting repair for broken joints?


My answer has to be divided into sections and each section will address joint types and a repair option when the joint edges break or become a problem. Do concrete floors need joints? Yes, concrete floors should be jointed. Random cracking will develop in concrete floors without joints. Random cracking occurs because concrete shrinks when it moves from its original plastic or wet volume state to its hardened volume. This shrinkage or volume loss of concrete occurs as it hardens. The friction of the base or soil against the bottom of the shrinking concrete restricts the concrete from moving freely, thus cracks develop. This is also true for pipes penetrating the concrete and other embedment. These embedments restrict the movement of the shrinking concrete and a crack will develop near the embedment or support column.

The first joint we can learn about is the Construction Joint. Your floors have construction joints where one lane of concrete was placed and finished and the next day or later another lane of concrete was placed along side of the older lane. Officially, a construction joint is the division between two successive placements of concrete. Reinforcement may pass through a construction joint. (See diagram A). The construction joints in your floors should be straight, and the edges should be unbroken. The way to maintain and repair construction joints is to clean them out and fill them with a rugged polyurea joint sealant. If the joint faces are not out of vertical alignment but the edges are broken or missing, a rugged polyurea joint sealant can also be the proper repair material.

The second joint we can learn about is the Contraction Joint. Your floors should have contraction joints already in the surface. Contraction joints are also called (crack) control joints or saw-cut joints. Contraction joints are cut into the concrete to prevent random cracking due to volume loss or shrinkage of fresh concrete as it hardens. Contraction joint cutting can be accomplished by a jointer hand tool or, more commonly, by a concrete saw cutting blade. Contraction joints are vulnerable to edge breaking or deterioration after the floor is put into service. This vulnerability can be overcome by filling the contraction joints and their deteriorated edges with a rugged polyurea joint sealant. This joint filling is most effective in non-moving cracks and fully cured slabs. For best performance new floors should be allowed to cure for a minimum of 60 days. Deteriorated contraction joints can be cleaned out and rebuilt with polyurea. (See diagram B)

L&M can develop a program for your entire organization and your maintenance contractor to protect new joints in your floors and to rebuild or repair the failed joints. The product we offer is a premium, 2-part rugged polyurea called L&M Joint Tite 750. This product is a two-component, self-leveling liquid. The most popular color is concrete gray, but other colors are available. L&M Joint Tite 750 can be installed in wide range of temperatures and can be opened to traffic in less than an hour. This means that your plant operations will suffer little to no down-time and your material handling machines will be able to roll smoothly across L&M Joint Tite 750 filled or repaired joints.

L&M Construction Chemicals is organized into regions in North America and outside of the North American continent. Our regional managers are trained and ready to assist you in helping you with your concrete floor problems. Contact us to locate the manager nearest to you. We look forward to solving your concrete floor and other concrete related problems.

Thanks for asking.