How to install a G1 crack monitor?
Correct installation of crack monitors on the substrate is essential to ensure their durability and prevent any detachment. If the installation conditions are not met, the fixing is unlikely to hold over time. Three fixing methods are available to measure crack evolution on one axis: using the supplied adhesive pads, bonding with epoxy adhesive, or mechanical fixing.
Preparing the crack monitor
Before fixing, it is recommended to position the sliding arm so that the dotted lines are equally visible on both sides of the gauge. This ensures maximum movement amplitude, both in opening and closing directions.
For gauges with a 0 on the measuring scale (G1), it is advised not to target zero to avoid complications when reading the vernier in reverse in the event of crack closure.
However, if you wish to benefit from maximum opening amplitude and the closing movement is expected to be small, or if the crack is very fine, it is perfectly possible to approach zero while remaining within positive values.
For Saugnac G1-type gauges before mid-2025, the foldable strip must be inserted into the sliding arm before installation. (New gauges are manufactured with a groove on the sliding tab, without a strip.)
Positioning the gauge on the crack
In the absence of specific constraints, it is generally recommended to place the measuring instrument at the widest point of the crack (as this is typically where it started to open), or if the crack is approximately the same width throughout, at the centre of the crack. The gauge must be placed in the direction of the crack movement, i.e. generally perpendicular to the crack, in order to best measure the movement and avoid any blockage.
For cracks several metres long, it is advisable to position several gauges for more accurate monitoring. Logically, the more measurement points are set, the more data will be collected to refine the analysis of crack evolution.
In general, the recommendations of building professionals who have carried out the diagnosis should be followed, as they will be best placed to propose the most appropriate monitoring solution for the problem at hand.
The different types of crack monitor installation
Crack gauges can be installed on a single axis in different ways depending on the type of substrate.
Adhesive pad fixing
G1-type crack gauges are supplied with technical adhesive pads that are weather-resistant, ensuring a durable fix. Ideal fixing conditions are between 0°C and 35°C, with a tolerance down to -10°C.
For adhesive pad fixing, the following conditions must be met:
- The substrate must be smooth: the rougher the surface, the smaller the bonding area and the higher the risk of detachment. To improve adhesion, the surface can be lightly sanded if necessary.
- The substrate must be dry: bonding cannot be carried out correctly on a damp surface. It is essential to ensure that the bonding surface is dry at the time of fixing. Once fixed, the bond will resist weathering (except for G1.1 models).
- The substrate must be clean: dust and greasy surfaces must be avoided in particular. If necessary, the surface must be cleaned beforehand.
If these conditions are met, simply remove the protective backing from the adhesive pads and apply the gauge on either side of the crack.
After application, firm pressure for 10 to 20 seconds ensures an effective bond.
Epoxy adhesive fixing
If the substrate is not suitable for adhesive pads, it is possible to reinforce the bond using two-component epoxy adhesive.
This fast-setting adhesive ensures optimal fixing of the crack gauge. It is a water-resistant adhesive that can even be submerged.
Before bonding, it is essential to ensure that the substrate is dry and clean. If the surface is damp and/or greasy, the adhesive will not set.
The adhesive is supplied with 2 mixing nozzles for combining the 2 components. Apply the mixture to both the substrate and the adhesive pads of the crack gauge. Hold under pressure for a few seconds to perfect adhesion.
Setting time is approximately 4 minutes. Full strength is reached after 2 hours.
Mechanical fixing
Mechanical fixing is carried out using the holes in the gauges along with wall plugs and screws.
The procedure involves drilling Ø4 mm holes to a depth of 30 mm into the substrate to receive the wall plugs.
Tightening is carried out with a screwdriver suitable for the Posidriv PZ2 screw head.
How to install a crack gauge in a corner?
From mid-2025 onwards
G1-type gauges are manufactured with a groove materialised by a bending zone on the sliding tab.
This groove facilitates bending of the sliding tab to achieve corner fixing without any additional accessory. The sliding tab must be bent at the marking zone to the desired angle.
Once bent to the desired angle, carry out the fixing using the chosen method: adhesive pads, epoxy adhesive or mechanical fixing.
Before mid-2025
The foldable strip supplied with gauges produced before mid-2025 allows crack monitors to be installed at an angle. The part features a thin section designed to guide and facilitate bending.
The strip must be bent to the desired angle before installing the crack gauge. To avoid any risk of breakage during bending, the material temperature should be a minimum of approximately 10°C. If the temperature is lower, we recommend warming the strip in your hands before bending. Bending must be carried out continuously (avoid sudden movements) and relatively slowly (approximately 3 seconds).
