It is not just as simple as reviewing the sketches above to determine the exact cause of the cracking either by Settlement of Heave. Many other factors have to be considered when making an evaluation, particularly a review of the site history and conditions. Careful identification of any differential movement and displacement of any surrounding structure can also help identify and produce a true fault analysis.
How to reduce or prevent settlement cracking
In order to prevent or reduce the risk of settlement you need to be very pro active with your builder or the construction team. Strict monitoring should be adopted, the foundation and floor slab should be compacted just before the pouring of the concrete or as close to it as possible. Ensure the operative who is operating the compactor covers the complete area paying particular attention to the corners. When choosing the type of concrete is it always better to use the strongest and many home builders now use a fiber mix concrete which has additional strength over a conventional concrete mix.
When the concrete has been poured it is imperative that it is allowed sufficient time to cure and has adequate hydration. In the hot summer months concrete should be poured as early in the morning as possible and after the initial hardness cover is achieved a fine water spray should be directed over it to slow down the accelerated drying by the heat and sun. The minimum time the concrete should be allowed to cure is 7 days. This means not allowing the builder to place any weight or start building on the slab. The concrete should have expansion slots or joints cut into it as soon as a hard crust is achieved allowing it to expand and contract without cracking the surface. The exterior grading around the slab should be slopped away allowing any surface rainwater to be driven away from the structure. No deep excavations should be allowed near to the structure such as digging for a pool until the concrete is fully cured and the surrounding ground has stabilized.
Remedies to existing settlement cracking
All settlement cracking should be monitored for further movement. Settlement should be covered under the builders warranty and it will generally be their responsibility to rectify it if it persists. It is always advisable to get an independent evaluation carried out and present it to the builder. Once the problem has been identified monitoring tabs should be placed adjacent to the widest part of the cracking which will give an accurate indication of how fast and the extent of the movement. All the cracks should be sealed with caulking to prevent water and insect ingress.
This one of the best monitoring devises available is a “Tell Tale” crack monitoring device. This glass or plastic slide rule type devise that is fitted securely over the crack. The exact location of the cross hairs in the scale window is recorded and reviewed after a period of time to determine exact movement.