There are 3 guarantees in the concrete business:
1. It will get hard
2. It will not be stolen once is gets hard
3. It will crack
While there is not a negative in the first two guarantees of concrete, the third often becomes a source of concern and to many contractors, a source of revenue. The evaluation and repair of these cracks is an art and a science. Experience and visual evaluation is the art of crack investigation that guides foundation experts towards a solution to repair. The science of crack evaluation requires proof and documentation to support the art.
Once a foundation crack has been identified to be caused by settlement, heaving, bowing or other force, the next step is to determine whether the crack is getting larger or if it has stopped. The seasons of the year will dictate part of this as will obvious changes in overall moisture content of the surrounding soils. If you are in an extended dry or wet period (over one year) or if an outside influence has changed (water pipe leaking). Determining the progression of the foundation crack is the job of a crack monitor.
Crack monitors are devices that give a recording of movement relative to each side of a visual crack. Crack gauges determine the size of a crack. The evaluation criterion for IBC and IRC is a gap of .064". This means that if the crack is smaller than .064" the crack will not allow water to penetrate and does not cause concern for the overall stability of the structure at the present time. If the crack larger and/or has ruptured the foundation, a cause for concern is viable and the evaluation and monitoring is necessary. Rupture is defined as a crack that has penetrated both sides of a foundation element. Crack monitors evaluate the movement across a crack or rupture over a period of time to help determine the nature of structural problems.
Crack Monitors consist of two overlapping acrylic plates. One plate is marked with a millimeter grid, the other with cross hairs centered over the grid. Once installed, any movement can be easily seen and then recorded on the Crack Progress Chart provided with each monitor. Crack Monitors can be used to determine whether existing cracks are stable or still experiencing movement with a record of this movement to substantiate methods of repairs. The structures owner can be assured, with proof of movement, before repairs or proof of non-movement after a repair has been completed. The proof of non-movement can be critical to dispel visual or mental suspicions that unfounded.