You notice a crack on your facade, a load-bearing wall or a ceiling. Your first instinct is to call in an expert to find out whether it’s active or stable. But here’s the reality on the ground: no serious expert can declare a crack active or stable after a single visit. A crack must be measured over time, and that’s precisely the purpose of the crack monitoring we set up at Cassini Expertise across the Alpes-Maritimes and the Var.
Why one visit is never enough
A crack is a dynamic pathology. It reflects movement in the building: differential settlement, clay shrink-swell, roof frame deformation, lateral thrust, vibrations… But at the moment of the visit, the expert is only observing a frozen state. They can measure the width, describe the pattern, identify the structural context, but they cannot know whether the movement has stopped or is still ongoing.
It’s like taking a photo of a car on the road: you see its position, but you don’t know if it’s moving or parked. To find out, you need to observe it over time.
The monitoring protocol: measure, date, compare
The crack monitoring we deploy relies on several complementary tools, chosen according to the configuration and the objective:
Plaster witness marks
Simple, inexpensive and very informative: a plaster pad is applied straddling the crack. If it breaks, the movement has resumed. Limitation: they don’t give an amplitude, only a binary signal (movement / no movement). They are fragile and can crack from an impact, a vibration, or the plaster’s own shrinkage, which can produce false alarms.
Screw-type witness marks
Two graduated plates fixed on either side of the crack, with an adjustment screw. They allow a direct reading of the gap. More robust than plaster, though still sensitive to impacts.
Dial-gauge crack meters
Precision instruments (accurate to 1/10th of a millimetre) that we use at Cassini Expertise. They measure not only the opening but also vertical and horizontal displacement. We install them at fixed reference points and take comparative readings at regular intervals. This is the most reliable device for documenting fine-grained changes.
Dated photos with fixed reference points
An essential complement: every visit produces photographs with reference markers (tape measure, graduated ruler, fixed architectural features). These photos build a visual record that lets you compare the crack’s appearance over time: widening, lengthening, branching, flaking…
Standard monitoring schedule
We recommend monitoring over a minimum of 12 months, with readings at Day 0 (installation), 3 months, 6 months and 12 months. This rhythm captures seasonal variation (clay shrink-swell in summer/winter, freeze-thaw cycles) and identifies a robust trend. In certain cases (disputes, insurance claims, nearby construction works), we adjust the frequency.
What monitoring reveals
Well-conducted monitoring provides three types of information:
Whether it’s evolving or not
Is the crack opening? Is it closing (rare, but possible after underpinning work or soil rehydration)? Is it staying stable? This is the baseline question, and it shapes everything that follows.
The speed of change
A 2 mm opening over a year doesn’t mean the same thing as a 2 mm opening over a month. The speed indicates how intense the phenomenon is and how urgent any repair work may be.
Correlations
Does the movement coincide with a drought period (clay shrinkage)? With the start of nearby works (vibrations, excavation, pumping)? With a repaired water leak (rehydration)? These correlations guide the diagnostic investigation, though they don’t in themselves prove direct causation.
Practical uses of crack monitoring
Property transactions
You’re selling a cracked property and the buyer is concerned. Monitoring already under way, with readings over several months showing stability, reassures the buyer and secures the sale. Conversely, if you’re buying, requesting monitoring before signing protects you: you’ll know whether the crack is evolving and can negotiate the price accordingly or make the purchase conditional on remedial work.
Natural disaster (drought) insurance claims
To obtain compensation under drought-related natural disaster cover (clay shrink-swell), you must prove that the cracks are recent or actively evolving. Monitoring with crack gauges and dated photos provides solid evidence for the insurer and the appointed loss adjuster.
Disputes with a neighbour
Excavation works, construction along a boundary, tree felling… If you suspect a link between a neighbour’s works and your cracks, monitoring lets you pinpoint precisely when they appeared or worsened. It puts the debate on an objective footing and can serve as evidence in legal proceedings.
Prior condition survey before neighbouring works
Your neighbour informs you of a planned construction, swimming pool, or excavation project. Having a condition survey carried out with witness marks installed BEFORE the works begin allows you to distinguish pre-existing cracks from any that appear during or after the project. It’s a simple, low-cost legal precaution.
The honest limits of crack monitoring
Let’s be clear: crack monitoring documents movement, it doesn’t identify THE cause. If the crack gauge shows a 3 mm opening over six months, you know the crack is evolving, but you still don’t know whether it’s due to foundation settlement, clay shrinkage, roof overload, a leak, a defective tie-beam, or a combination of several factors.
Monitoring is therefore a diagnostic step, not a conclusion. It feeds into the structural assessment, which itself draws on analysis of the building, the soil, the surroundings, the plans, the history of works carried out… At Cassini Expertise, we systematically pair monitoring with Trotec-based investigation (moisture meter, thermal camera) and an analysis of the geotechnical and structural context.
Another limitation: 12 months of monitoring may not capture a slow cyclical phenomenon (every 2-3 years) or a very gradual movement. In certain contexts (expansive clays, older buildings on heterogeneous soil), we recommend extended monitoring.
Frequently asked questions
How much does crack monitoring cost?
The cost depends on the number of measurement points, the duration, accessibility and the type of device used. Expect a few hundred euros for simple 12-month monitoring with witness marks, and more if you opt for precision crack gauges or closer-interval monitoring. We provide a tailored quote after an on-site visit.
Can I install the witness marks myself?
Technically yes, but the evidentiary value will be limited. Monitoring carried out by an independent expert, with calibrated instruments, a formal protocol and a dated report, carries far more weight with an insurer, a court, or a buyer. If your goal is simply to keep an eye on things yourself, off-the-shelf plaster witness marks may be enough.
What happens if monitoring shows the crack is evolving?
We provide an interim and a final report documenting the changes. If they are significant, we recommend an in-depth structural assessment to identify the cause and recommend appropriate remedial work (underpinning, drainage, tie-beams, localised repair…). In some cases, we refer you for a geotechnical study.
Is monitoring mandatory when selling a property?
No, but if the buyer commissions an assessment that flags evolving cracks with no monitoring in place, they may claim a hidden defect. Conversely, providing reassuring monitoring data makes the transaction smoother. It’s a matter of transparency and risk management.
Cassini Expertise: 15 years of experience across the Alpes-Maritimes and the Var
With 15 years’ experience in public works and project management, Cassini Expertise operates as an independent building expert across the Alpes-Maritimes (06) and the Var (83). We equip our monitoring assignments with precision dial-gauge crack meters, screw-type witness marks, and Trotec instruments for hygrometric and thermal analysis. Every visit results in a dated photographic report, quantified readings, and a clear technical summary.
Whether you are an owner, a buyer, a property manager, an insurer, or a party to a dispute, we put our expertise to work for a rigorous, impartial diagnosis.
Cassini Expertise
Independent building expert
Antibes – Alpes-Maritimes (06) & Var (83)
Phone: 04 22 46 06 04
Email: [email protected]
Related articles
- Crack audit before buying: the checklist
- Clay shrink-swell (RGA) crack diagnosis in the 06-83
- Buying a cracked house in the Alpes-Maritimes
Cassini Expertise
Expert du bâtiment indépendant — Antibes (06·83·13·40)
📅 Mis à jour le 26/09/2026 — Cassini Expertise, expert bâtiment indépendant (06·83·13·40).