Which type of crack gauge for your crack?
To determine the ideal gauge for accurately measuring the progression of a movement or a crack, it is essential to assess your specific needs. At Saugnac, we offer a diverse range of nearly twenty products, suited to monitoring all types of structural movement.
This guide helps you choose based on your situation: the movement to monitor, how readings will be taken and your on-site constraints. Each solution is then described in detail.
Measuring a width or monitoring a change? To simply measure the width of a crack at a given moment, use a crack ruler or a triangular gauge. To find out whether the crack is moving, you need a monitoring gauge, installed across the crack and read over time: that is what this guide is about.
Choosing your gauge in 3 questions
What movement do you want to monitor?
- A crack that opens and closes: 1-axis monitoring.
- A crack that may also slide, for example in the event of differential settlement: 2-axis monitoring (opening and shear).
- A step forming between two slabs or two structures: misalignment.
- A wall or balcony that is tilting: tilt.
- Movement in all directions: 3-axis monitoring.
- A beam or ceiling that is deflecting: deflection.
- Two walls several metres apart moving away from each other: extensometer.
If you are unsure between 1 and 2 axes, choose 2 axes: you will not miss any data useful for the diagnosis.
On-site or remote readings?
On site, mechanical gauges and the E1 gauge are read at each visit, and readings are tracked in the free Saugnac.app application.
Remotely, connected gauges (R1, R2, R5, R20, R130…) send their readings automatically, from every hour to once a day, together with temperature and humidity, and alert you as soon as a threshold you have set is exceeded. They come with a 1-year subscription included (then €49 excl. VAT per year) and run for 2 to 8 years on their battery depending on the settings. This is the right solution if the crack is difficult to access, if visits are infrequent or if you need to react quickly.
What are the on-site constraints?
Expected range, environment, appearance of the substrate, number of points to monitor, who will take the readings: the table below matches the most common situations with the right gauge.
Your situation, our recommendation
| Your situation | Our recommendation |
|---|---|
| You are not comfortable with vernier scales, or you want to avoid parallax errors | G1+ (simplified reading to 0.05 mm) or E1 (digital reading to 0.01 mm) |
| You have many cracks to monitor, or you prefer a device with a digital readout | E1: digital reading to 0.01 mm, a single gauge for all points, only the mounting plates stay in place |
| Indoor cracks, in dry rooms | G1.1, the most economical |
| Fine substrate: stone, heritage buildings, high-end interiors | G1.2 transparent gauge, or E1 with its transparent mounting plates |
| Aggressive environment, or greater precision with a gauge left in place | G1.5 in carbon, to 0.02 mm |
| Wide crack or large movements expected | G1.3 (range up to about 17 cm), or R2 for remote monitoring (100 mm) |
| No regular readings possible, but minimum and maximum needed | G2, which records the extremes without a battery |
| Crack difficult to access, or site visits not possible | R1 connected gauge |
| Be notified as soon as a movement exceeds a threshold | All connected gauges: R1, R2, R5, R20, R130…, with adjustable alert thresholds |
| Ongoing works, rapid movements | R2 or R5 with Monitoring+ mode, for closely spaced readings over a limited period |
| You do not want to leave the gauge on site | E1, G5+ (tilt) or 3Dim (3 axes): removable gauges on mounting plates |
| Crack in a corner | G1 family gauges (grooved movable arm) or E1; aluminium angle bar for the G1.3 and G2 |
| Monitoring temperature and humidity only | R10 connected gauge |
Crack gauges for the most common cases: crack opening
Monitoring cracks on 1 axis
The “standard” case involves monitoring the opening and closing of a crack. This is single-axis crack monitoring.
To help you compare, here are the main characteristics of 1-axis monitoring gauges, each described in detail below.
| Gauge | Resolution / range | Key feature |
|---|---|---|
| G1.1 | 0.1 mm · ≈ 20 mm | Indoor only, the most economical |
| G1 | 0.1 mm · ≈ 20 mm | The classic, indoor and outdoor |
| G1+ | 0.05 mm · ≈ 25 mm | Simplified reading, no vernier |
| G1.2 | 0.1 mm · ≈ 20 mm | Transparent, discreet |
| E1 | 0.01 mm · ≈ 25 mm | Digital reading, removable gauge |
| G1.5 | 0.02 mm · ≈ 45 mm | Carbon, aggressive environments |
| G1.3 | 0.1 mm · ≈ 170 mm | Wide cracks |
| G2 | 0.1 mm · ≈ 25 mm | Records minimum and maximum |
| R1 | 0.01 mm · ≈ 23 mm | Connected, remote readings |
| R2 | 0.01 mm · ≈ 100 mm | Connected, large range |
An easy-to-read crack gauge
If you want the easiest to read and most accurate gauge for indoor or outdoor use, choose the G1+.
Its patented reading system requires no knowledge of vernier scales, avoids parallax reading errors (if you are not perfectly aligned with the gauge) and allows readings down to 0.05 mm. Its range is about 25 mm.
The classic gauge if you can read a vernier scale
If you can read a vernier scale and need to carry out indoor or outdoor monitoring, choose the G1.
A simple and effective operation.
The Saugnac app provided even allows readings to be taken with a smartphone, making it easier to read the vernier scale.
For indoor crack monitoring
If you only need to monitor cracks indoors, choose the G1.1.
More economical, it is designed exclusively for installation inside buildings and dry rooms.
A transparent crack gauge
If you prefer a more discreet solution, choose the G1.2 gauge.
Transparent, it works in the same way as the G1 and is suitable for outdoor use, but is less visible.
An economical digital crack gauge
If you are looking for something more precise, more discreet and more cost-effective when you have many cracks to monitor: the E1 gauge with digital readout, offering a resolution of 0.01 mm, is the right solution. It is supplied in a carrying case with 5 pairs of mounting plates, enough to monitor 5 cracks on 1 axis.
Its transparent mounting plates are fixed on either side of the crack using the supplied fixings, and the gauge clips into the plates to take the reading.
The advantage of this system is that only the mounting plates remain on the substrate — transparent and compact in size (33 mm in diameter and less than 10 mm high).
Furthermore, this solution minimises surface damage, all the more so as the plates are made from a durable material (PA12), the same used for boat windscreen components.
As the reading is digital, no specialist knowledge is required, and replacement plate sets cost less than G1 or G1+ gauges.
Crack gauges for more specific single-axis monitoring requirements
Some cracks in walls have more specific requirements and call for the use of a suitable gauge.
A stainless carbon gauge
In certain cases, particularly in aggressive environments and/or where greater precision is required while leaving the gauge in place, you may opt for the G1.5 gauge, a carbon gauge with a resolution of 0.02 mm, a range of about 45 mm and a very low coefficient of thermal expansion. It is supplied with a magnifier for reading the vernier and self-tapping screws for mechanical fixing, which is recommended.
The solution for wide cracks
If your crack is more than 15 cm wide, or if the anticipated crack displacement exceeds 2.5 cm, it will not be possible to use a G1 or E1 type gauge; you should instead opt for a G1.3 gauge, which can measure cracks with large openings and/or significant variations: a range of up to about 17 cm, with a fixing span of up to 25 cm. Hammer-in wall plugs are supplied.
To record minimum and maximum readings
If you need to know the maximum and minimum readings without being able to take them regularly, you can opt for the G2 gauge, which records the maximum and minimum measurements using a graphite pencil lead, read to within about 0.5 mm.
A simple and effective method requiring no battery, to determine how far the crack opens and closes.
Choosing the gauge according to crack orientation
The orientation of the crack does not influence the choice of gauge. The principle is to position the gauge straddling the crack. If the crack is horizontal or oblique, simply orient the gauge correctly, perpendicular to the crack.
What about corner cracks?
All crack gauges in the G1 family are manufactured with a groove forming a fold line on the movable arm. This groove makes it easy to bend the movable arm for corner installation without any additional accessory.
For environments subject to significant stress, or for other gauges (G1.3, G2), it is also possible to purchase an aluminium angle bar as a supplement.
The E1 digital crackmeter is specifically designed for corner monitoring, thanks to its transparent mounting plates that allow precise fixing on two perpendicular surfaces.
Remote crack opening monitoring with connected sensors
The compact version
To carry out regular readings without on-site visits, or because the crack is difficult to access, the solution is to use a connected crackmeter: the R1 gauge.
This gauge is equipped with 3 sensors (linear displacement to 0.01 mm, temperature and humidity) to collect all the information needed for diagnosis.
Ready to install, this gauge includes all the necessary components to transmit data to the application (communication module and subscription). No IT knowledge is required to configure the gauge — everything is done in a few clicks. Readings are taken every 1 to 24 hours depending on your settings, and the gauge runs for 2 to 8 years on its battery.
The version with large-range sensor and Monitoring+ mode
The R2 connected crackmeter is a version with a remote sensor, specially designed for monitoring cracks with large displacement amplitudes. Thanks to its external linear sensor, it can measure and track the evolution of an opening of up to 100 mm, while maintaining high long-term accuracy.
The compact and robust electronic enclosure also integrates a relative humidity sensor and a temperature sensor, providing a comprehensive view of the environmental conditions influencing the behaviour of the structure. This multi-parameter approach enhances the quality of structural diagnosis and facilitates the analysis of mechanical phenomena related to climatic variations.
The R2 also features Monitoring+ mode, an enhanced surveillance mode that allows the acquisition frequency to be increased to one reading every 2 minutes. This functionality is particularly suited to critical phases (construction works, rapid movements, sensitive temporary instrumentation), when rapid detection of variations is essential.
Versatile, accurate and easy to integrate, the R2 gauge is an ideal solution for continuous and reliable monitoring of large-amplitude cracks.
Crack gauges for walls with opening and shear movement (2 axes)
The aim is to account for movement on two axes. For example, in the event of differential ground settlement, the crack may not only open but also shift laterally, as the movement occurs along two axes. It is therefore necessary to choose a solution that allows both axes to be monitored.
More generally, if you are not certain about the type of movement involved, it may be more prudent to opt for a solution that enables measurement on both axes. This ensures that all the data necessary for a complete analysis and interpretation are collected.
To carry out 2-axis monitoring, we offer 3 solutions:
A mechanical solution with the G6 gauge, which features 2 vernier scales and allows movement to be monitored on 2 axes, with a resolution of 0.1 mm horizontally and about 0.33 mm vertically. Readings can be logged directly in the app.
An electronic solution with the E1 gauge, which also offers the possibility of 2-axis monitoring by positioning 3 mounting plates. The X and Y projection calculation is then carried out in the app. Full instructions are available on the E1 gauge product page.
A connected solution with a 2D kit based on 2 R1 gauges and specific fixings.
Crack gauges for misalignment cases
When faced with problems such as a sagging ceiling or floor, a slab failure, or the misalignment of a column or wall, the G3 gauge offers a versatile solution.
Its unique cubic design allows the progression of misalignment to be monitored, whether horizontal or vertical, offering exceptional flexibility. With a resolution of 0.1 mm on the vernier, corresponding to 0.2 mm of movement, and a measuring range of about 35 mm, the G3 delivers remarkable accuracy and its use is simplified by the free Saugnac.app application.
Fixation can be carried out on any of the 5 faces of the cube (floor, wall, ceiling or skirting board) with the adhesives supplied, and as an option, a mechanical fixing with an intermediate plate is available.
For a detailed graphical record of the progression, an optional recording kit is also available, ensuring complete and accurate monitoring of misalignment over time.
To remotely monitor the settlement of a bridge or structure subject to temperature variations, the R2.P connected gauge measures vertical displacements to 0.01 mm while absorbing the thermal expansion of the structure.
Crack gauges for wall or balcony tilting
Inclinometers differ mainly in their resolution and how readings are taken:
| Gauge | Resolution | Key feature |
|---|---|---|
| R5 | 0.005° | Connected, remote readings on 2 axes |
| G5 | 0.03° | Mechanical, stays in place |
| G5mini | 0.06° | Mechanical, compact and economical |
| G5+ | 0.03° | Mechanical, removable on mounting plates |
The connected version
We offer a connected inclinometer (R5 gauge) for remote monitoring of tilt progression on 2 axes.
This inclinometer offers a resolution of 0.005° (i.e. 0.0873 mm/m) over a range of ±45° and is also equipped with an ambient temperature and humidity sensor.
It is supplied ready to install with all fixings and a 1-year subscription included, and is configured very simply via the application. Its Monitoring+ mode increases the reading frequency over a limited period, for example during works.
The classic mechanical version
We also offer mechanical inclinometers from the G5 range. These inclinometers, based on the effective and simple pendulum principle, are designed to monitor the tilt of a structure. All these gauges can be fixed flat or perpendicular using angle brackets.
Whatever the tilt monitoring requirement, the G5 gauge enables monitoring of angle variations of 0.03° (0.1 mm on the vernier).
The economical version
If the size of the inclinometer and/or the price are priorities over measurement resolution: the G5mini gauge is an alternative.
It is half the size of the G5 gauge, less expensive but with a resolution that is twice as low (resolution 0.06°).
The removable solution
If you have numerous monitoring points and/or do not wish to leave the gauge in place, the G5+ gauge with a mounting plate is recommended. This gauge is removable and is positioned magnetically on a mounting plate to take the reading (plates sold separately). It offers two advantages:
- It does not remain permanently on the substrate: after the reading has been taken, it can be stored in its carrying case, eliminating any risk of damage or deterioration.
- Purchasing mounting plates is more cost-effective than purchasing gauges (and protective covers, where applicable).
For monitoring movement in all 3 dimensions
If you need to monitor the displacement of one structure relative to another in three dimensions using a single instrument, the 3Dim gauge is the universal tool that allows the millimetric progression of structures to be monitored simply and accurately in three dimensions.
Equipped with three vernier scales (0.1 mm in translation, 0.2° in rotation) and an Excel calculation spreadsheet supplied on request, this solution can track any type of movement over a range of about 25 cm. Its installation is based on the fixing of two magnetic mounting plates that serve as the measurement reference. This crack and deformation measuring instrument is removable and is only positioned on the plates when taking a reading. This system is, for example, far simpler to install than a vinchon.
In simpler configurations requiring three-dimensional monitoring, it is also possible to use a combination of instruments measuring two axes and misalignment — for example, a G6 + G3 gauge or an E1 + G3 gauge.
It is also possible to carry out 3-dimensional remote monitoring with the 3D remote monitoring kit.
Measuring instruments for beam / ceiling deflection
The G130 gauge from Saugnac stands out for its ability to measure the evolution of deflection, wall overturning or compressive deformation of a structure with a fine resolution of 0.1 mm, corresponding to 0.2 mm of movement.
This custom device, installed between two anchor points 3 to 15 m apart, offers a solution adapted to specific problems, requiring a thorough study of each case in order to propose a tailored solution.
Each G130 solution is supplied with installation instructions and a drawing specifically written according to the constraints of each project. This personalised approach ensures optimal integration of the monitoring device into the user’s specific environment.
The R130 gauge represents the connected evolution of the G130. It retains the robustness and accuracy of the original device while integrating full connectivity for remote, real-time monitoring of deflection, wall overturning or structural deformation.
With a resolution of 0.01 mm and integrated temperature and humidity sensors, it provides precise, contextualised data, transmitted directly to the Saugnac.app platform without any manual intervention. The user benefits from continuous and secure monitoring, with the ability to configure alert thresholds to be notified in the event of abnormal movement.
Monitoring the separation between 2 points several metres apart
The Saugnac recording extensometer, also known as the G20 gauge, enables precise monitoring to the nearest 0.1 mm of the progression of the distance between two points separated by several metres and located at several metres height.
This extensometer provides an accurate check of the constancy of the distance between two parallel walls or two distant points on the same wall. This is typically the case for the outward thrust of church walls. Thanks to its remote-reading enclosure, readings are taken at eye level. Furthermore, as the solution is based on the G2 gauge, a graphical record of minimum and maximum values is produced, read to within about 0.5 mm.
The extensometer is also available in a connected version for remote monitoring of the separation with the R20 connected extensometer. This gauge is based on the R1 connected crackmeter and therefore enables remote monitoring of the evolution of the distance (resolution 0.01 mm), temperature and humidity.
This proven technology guarantees reliable and accurate monitoring of variations over time, offering an ideal solution for projects where the constancy of the distance between two points is critical.
