Movement in buildings occurs all the time. In majority of cases the extent is too small to be noticed. It is when the movement is great, large cracks in walls will appear, the problem needs to be addressed and resolved.
It is important to recognise that they are the visible symptom of possible problems.
Some causes of cracking include: settlement or foundation erosion, decay of materials, "vandalism" by renovators, structural failure, change in materials or geometry, and moisture and temperature changes.
1 Foundation Settlement
In foundation piers and piles, general cracking is often due to settlement or rotation of the pier footing.
2 Vertical Cracking
Vertical cracking or bulging of a masonry foundation wall is often due to physical deterioration of the pier from exposure, poor construction or overstressing.
3 Horizontal Cracking
Horizontal cracking or bowing of a masonry foundation wall may be caused by improper backfilling, or by swelling or freezing and heaving of water saturated soils adjacent to the wall.
4 Differential Settlement of foundation
Differential settlement of a masonry foundation wall may be caused by many different things including soil consolidation, soil shrinkage, soil swelling, soil heaving, soil erosion or soil compaction.
5 Differential Settlement of a chimney
Differential settlement of a chimney is often caused by inadequate foundations which may cause the chimney to lean and crack.
Monitoring Crack Movement
Assess cracks in buildings is important to establish whether the cracks in walls or ceilings are increasing in size and if movement has occurred.
The best method for measuring cracks is by installing a crack monitor or ‘tell-tales’ (generic name).
A crack monitor or tell-tales, is a simple and effective gauge to measure the movement of cracks in brick, concrete, or masonry structures.
Avongard Tell-Tale Crack Monitor
A crack monitor consists of two overlapping acrylic plates. One plate is white with a black millimeter grid, while the other is transparent with red crosshairs centered over the grid.
Once the crack monitor is in position across a crack, any movement will be recorded by the new position of the crosshair vertically or horizontally on the grid. This allows anyone to easily access and track the crack movement.
By utilising a crack monitor to monitor the movement of a crack, you will be able to build a picture of evidence, assess if the movement is still accruing and the direction. The tell-tales should be left in place for as long as possible to establish whether the crack is moving or not.
Positioning a Crack Monitor
Setting up a crack monitor is a simple process. When a crack has been identified, position the crack monitor over a suitable location that is accessible. You will need to revisit to take readings on a regular basis.
• Position the monitor over the crack with the vertical "0" line on scale parallel with the crack to be measured.
• Fix the monitor with screws or adhesive.
• Cut the transparent tape holding the two plates of the scale on the monitor in a fixed position with a sharp knife.
• Over time, the degree of movement on either side of the crack will be measured as the two plates slide independently of one another.
Advise on fixing the Avongard Tell-Tale
Ideally the Avongard Tell-Tale should be fixed with screws and adhesive reducing the risk of tampering if fixed with screws alone. We can supply the correct size fixings and adhesive.
On some surfaces there is no option but to use only adhesive. The adhesive must fully cure before the pegs are removed. The time taken for the adhesive to cure will depend on the ambient temperature, but the tell-tale must be held in position until the adhesive has hardened sufficiently for it to support the weight of the crack monitor.
Some customers use Blu-Tack to hold the crack monitor into position until the adhesive cures.
Taking Readings
All cracks monitors should be supplied with copies of a record sheet to record concurrent visits.
Record the position of the red crosshair
Once the crack monitor has been installed, record the position of the red cross on the grid for 6 – 8 weeks. Extended readings can be undertaken, but additional sheets will be required.
Improved measuring accuracy can be undertaken with a pair of calipers and using the Avongard Tell-Tale Plus. The resolution is improved to +/- 0.1mm
Use calipers to improve measuring accuracy
Monitoring Cracks Using the Avongard Crack Monitor
A recommended crack monitor is manufactured by Avongard who produces a number of professional crack monitoring systems. Formed in 1976, Avongard recognised there was a need for a simple but reliable calibrated gauge for the monitoring of cracks.
When utilising an Avongard tell-tales, you will be reassured that they are manufactured to the highest standard and quality. Avongard products are printed using the silicone pad and etched metal plates producing a finer and higher quality print.
