Cracks And Expansion Joints
What is the best way to handle cracks and expansion joints in the concrete with a resinous floor coating installation?
It is first important to understand why the cracks and joints are there. The expansion joints are form in the wet concrete or cut shortly after the placement of the concrete to allow for movement. Concrete shrinks when it dries. Expansion joints when placed properly and frequently enough will limit cracking to the location of the expansion joints. Crack most often occur most often due to lack of expansion joints. They may also occur as a result of concrete defects such as settling of the concrete or from abnormal abuse. It is important to resolve any concrete related problems causing the cracking before attempting to repair the issue.
There are several ways to address expansion joints and cracks as a result of shrinkage. The most obvious way to fill expansion joints is to fill the joint with a flexible joint sealant. The most cost effective joint sealants are usually single component urethane joint sealants. The may be supplied in caulking tubes or in bulk packaging. A backer rod or aggregate if often used to prefill the joint to prevent the joint sealant from sagging and limiting the amount of sealant needed for the repair. These are available in self-leveling formulations and are relatively easy to apply and are used on coated and uncoated floors and in some cases used after an epoxy floor or epoxy resurfacer has been installed. The newly installed floor can be re-sawcut through to the original sawcuts and filled allowing for the slab to move.
If speed is an issue the use a two part joint sealant such as a fast cure polyurea joint filler may be used in much the same way a single component polyurethane joint sealant with the added speed of a two part chemically catalyzed polyurea sealant. The joints may be overfilled and the excess trimmed providing a smoother look the control joint.
A third way to address filling of expansion joints is by filling with a two component patching filling compound. 100% solids epoxies along with aggregate or thickening flour are often used to patch and fill holes and cracks. They dry quickly and are useful for floor coating installers who can go overtop of the repair with a resinous flooring system. The shortfall to most epoxies is their lack of flexibility. This can be particularly problematic for expansion joints. One remedy for this is the use of a more flexible resin. This flexibility may still be limited if covered over with and rigid epoxy floor system.