The Slab Heave Inspection

The Inspection

The initial visual inspection should be scheduled as soon as possible after the telephone conversation. Giving excellent service to owners of homes with cracked houses is a priority. They need to be assured that you are giving their problem the attention it deserves.

On arrival, ask for the home-owner’s recollection of the order of damage appearing. How long ago did it appear? Which room did it appear first? Has the home-owner prepared a crack diary?

You need to gain an insight into the timeline for the damage appearing. You will need this information later when you are assessing seasonal moisture influences in the office.

Take the time to tour through the house and check each room with the home-owner present. I use this tour to get a feel for the building and to gain the home-owner’s trust for full access to the rooms  later in the investigation.

Take note of any particular damage that the home-owner points out. Ensure this damage is recorded and categorised later.

If you have already decided that the house could be suffering slab heave, and the original plans are not available, allow enough time to use a laser measurer to lay out the floor plan. Show windows and doors and steps in the floor plan sketch.

The formal recording part of the inspection consists of the following sections:

  1. Take a photo of the number on the letter box. This is to help you find the start of the photos and to remember the street address of the property.
  2. Take photographs  of the external facades of the building. Photograph all four sides of the building. This will help later with identification of crack location and compliance of the building with the original drawings.
  3. Start at the front left corner of the property and work around the building in a clockwise direction. Photograph and record the location and nature of damage to the external surfaces of the building. Include cracks and gaps in the external walls, soffits and pavements. Use the AS2870 guidelines for classifying the damage. Finish the external damage survey at the point you started. Use the external damage survey template.
  4. Record instances of poor soil moisture maintenance including air-conditioners that discharge to the ground, hot water systems that discharge to the ground, evaporative air systems that discharge to the ground, dripping taps located against the building, shallow indentations in the ground against the building, irrigation systems with sprinkler heads located against the building, swimming pool pavements that direct water towards the building, large trees within their mature height form the building, ground that falls towards the building, garden beds that are built against the building, garden beds that dam water against the building. Record areas of lawn that are unusually dry or wet (in comparison to the neighbour’s yard and to the remainder of the yard itself). Lush green lawns are an indication of moist ground conditions so examine the surface soil moisture conditions and note the condition of the lawn.
  5. Record the location of brick control joints.
  6. Starting at the front door and work around the inside of your building in a clockwise direction – keeping the wall to your left hand side. Record all internal damage including cracks in walls, gaps in cornices and gaps under walls. Measure crack widths using the crack width gauge. Photograph damage as you record it. Record point of original of the crack (where it is the widest) and the direction of the crack. Photograph your record pad at relevant times to help align the damage survey with the photos. Record cracks in ceiling cladding as you progress. Finish at the point in the house where you started. Use the internal damage survey template.
  7. Using a digital water level, record floor surface levels throughout the entire property including external patio areas under the main roof. Record levels at locations in each room that are easy to find again – beside windows, in corners of rooms and in the middle of large rooms. See the tips for zeroing the water level. See the tips for recording the levels at changes in floor covering. See the tips for recording the type of floor coverings.

Take general internal photos to help you remember the layout of the rooms. These will help when you try to reconcile photos of damage around windows and doors. The window and door furnishings are often different in each room.

That’s it. Thank the home-owners for their time and cooperation. Remember to take your water level and camera.

Reduce the Slab Surface Levels

The numbers you recorded during the slab survey are meaningless until you reduce the levels. Take the thickness of the floor coverings into account and reduce the height of all levels back to the top of concrete or top of timber (for houses on stumps). Then reduce the levels back to a zero datum.

You should end up with a slab survey with all of the points recording a height difference to the datum in millimetres.

Now prepare a slab contour plan. See the section on preparing contour plans for more information on how to do this.

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How to Identify and Fix Slab Heave