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Fine, shallow cracks that interlace into a network across the surface of an epoxy coating are called crow’s-foot cracking (crazing) in this article. The most important point when encountering this phenomenon is to establish where the cracks sit: only in the epoxy coating, or already penetrating down into the concrete substrate beneath. Those two cases have different causes and different remedies, even though at a glance they both look like “a cracked floor”.
This article discusses only crow’s-foot cracking in the epoxy coating: causes from the coating itself, from application, and from the service environment, together with remedies at the level of principle. This article does not repeat how to repair substrate cracks before application, nor does it set out the detailed patching process step by step. Readers who need those two subjects can compare: the article Concrete Floor Preparation Before Epoxy Coating: Grinding, Crack Repair, Moisture Testing covers substrate treatment before application, the article Localized Epoxy Floor Repair: Patching and Recoating Individual Areas sets out the localised repair process, and the article Epoxy Peeling, Bubbling and Discoloration: Causes and Fixes is the general diagnostic framework for other surface failures.
Illustration: a close-up surface with a network-pattern crack. This is a stock illustration of the crack pattern, not a photograph of a Kadier epoxy floor. Photo: Chris F on Pexels.
1. Identification: cracks in the coating, or cracks from the substrate?
Crow’s-foot cracking in the coating usually takes the form of a network of fine, shallow lines spread across the coating surface, without forming a single long crack running through. The surface on both sides of a crack usually remains at the same level, without displacement, and the crack does not keep extending into a long line in one particular direction. Those are signs suggesting the damage is confined to the coating.
Conversely, a crack originating in the concrete substrate is usually a distinct, long line, possibly accompanied by a level difference between its two edges, widening over time, or reappearing in exactly the same place even after the coating has been redone. When those signs are present, simply applying another coat of paint over the top will not resolve the cause, because substrate movement continues to act on the coating. Such a case needs a substrate survey first, following the direction of the substrate preparation article linked above, rather than being treated as coating cracking.
One further note: not every fine line on the surface is crow’s-foot cracking of the coating. Scratches from dragging heavy objects, marks from concentrated loads, or surface stains can look like cracks at a quick glance. Observing closely under raking light, checking whether the line penetrates into the coating or only sits on the surface, and seeing whether it develops into a network, will help distinguish before deciding on a remedy.
2. Causes from the coating and from application
The most common group of causes of crow’s-foot cracking in the coating relates to how the coating was formed and the conditions during application.
First, mixing and application not in accordance with the product instructions. The ratio between the paint component and the hardener, the degree of mixing, and the usable time of the mixture after mixing are all specified by the manufacturer for each specific product. A wrong mixing ratio or uneven mixing can cause the paint film to cure non-uniformly: some spots hard and brittle, others weak, and the surface easily cracking in a network pattern under stress. All mixing operations must therefore be checked against the technical documentation of the exact product in use; experience with one product must not be transferred to another.
Second, a coat thickness and number of coats unsuited to the system design. A coat applied too thickly in a single pass can dry on the surface quickly while the inside has not yet cured, creating shrinkage stress on the surface and causing cracks. Conversely, a coat that is too thin, insufficient to form a continuous film as the system design requires, is also easily damaged by mechanical and thermal action. The correct thickness is not a single number common to all coating systems but belongs to the design of each system — for example, the roller-applied system and the self-levelling system have different coat structures. Readers can compare the system structures via the RollCoat roller-applied system and the LevelFlow self-levelling system.
Third, application outside the conditions permitted for the product. Temperature, air humidity and substrate moisture, draughts, or direct harsh sunlight during application and curing all affect film formation. A surface drying too quickly, or a lower coat not yet ready to receive the next coat being overcoated, can leave a high-stress paint film that is prone to crow’s-foot cracking afterwards. Similarly, coating over an incompatible old coat, or over a surface that has not been properly cleaned and treated, gives poor adhesion and a coating that does not work as a unified system.
3. Causes from the service environment
Even when application was correct, an epoxy coating still works in an environment subject to change. Cured epoxy is a hard film with limited elastic deformation capacity. When the concrete substrate expands and contracts with temperature, when the floor is subjected to vibration from machinery, or when loads change repeatedly, the stress transferred to the hard coating can be released as a network of fine cracks on the surface instead of plastic deformation. Areas subject to large temperature differences, near entrances, areas exposed to hot sun followed by sudden cold, or areas with frequent vibration are where this phenomenon appears more readily.
Chemicals and cleaning methods also contribute to making the surface brittle over time. Strong cleaning chemicals unsuited to the coating system, solvents, or leaked chemicals left standing on the floor can all degrade the coating surface. For outdoor floors or areas with direct sunlight, UV is also a factor that ages the surface of many conventional epoxy systems. These effects usually do not cause cracking immediately after application but emerge gradually, accompanied by other signs such as discoloration, surface dullness, or loss of gloss. When crow’s-foot cracking is seen together with those signs, the history of use and cleaning must be considered, not only the moment of application.
Finally, service life is also a factor. Every coating wears and ages gradually during operation. Crow’s-foot cracking appearing after a long period of use, spreading widely and accompanied by surface wear, may be a sign that the system has reached the stage where a full reassessment is needed, rather than treatment of a few isolated cracks. The article on when to recoat a whole floor will be the next item in the failure group; here only the principle is stated: widespread cracking across the whole floor and localised cracking in one area are two different levels and should not be treated the same way.
4. Remedies, at the level of principle
The first principle is to deal with the cause before recoating. If the cracks are confined to the coating only, are not spreading, are not peeling, and the cause has been identified, the approach is to restore the coating in that area with a compatible coat system, after the surface has been properly prepared. Applying a new coat over a cracking coat without treating the surface and without identifying the cause usually only hides the cracks temporarily; while the old stress remains, cracks may reappear through the new coat.
The second principle is to preserve the compatibility of the coating system. The recoat must be compatible with the old coating remaining on the floor, from paint type to primer and topcoat systems, and must be applied under conditions permitted by the product’s technical documentation. Mixing different coating systems, or using a single topcoat in place of the whole designed coat system, both risk creating a non-uniform film that cracks again. The detailed technical sequence for patching and recoating individual areas is given in the localised repair article linked at the start of this article; this article does not repeat those steps.
The third principle is to distinguish localised scope from whole-floor scope. Crow’s-foot cracking in one area only, with a known cause that has been eliminated, is suited to localised treatment. Cracking spread across the whole floor, cracking recurring many times in the same place, or cracking accompanied by peeling, blistering, or signs of substrate movement, requires a general survey before deciding whether to recoat or to recoat the whole floor. Where the substrate is suspected to be the cause, return to the survey and substrate treatment step; do not rush to apply a new coat to hide the cracks.
The fourth principle is post-treatment inspection. After the coating has been restored, the area needs to be monitored through a cycle of use: do cracks reappear, does the coating peel at the edges, and are colour and gloss uniform with the surrounding area? This monitoring helps confirm whether the cause has truly been dealt with or merely covered up.
5. Prevention for new application
Preventing crow’s-foot cracking starts at the coating system selection and application design stage, not at the repair stage. The coating system needs to suit the function of the area: loads, chemical contact, temperature variation, and the actual cleaning conditions of the factory. A system suited to a dry, lightly loaded area is not necessarily suited to an area subject to vibration, heat, or frequent chemical contact.
Next is full compliance with the product’s technical documentation throughout application: mixing ratio, application conditions, waiting time between coats, thickness of each coat, and curing time before bringing the floor into service. These values differ between products and are only valid when matched to the specific product. Applying the correct process, controlling the application environment, and accepting each coat before applying the next are far more effective preventive measures than repairing after cracks have appeared.
Finally, correct operation and maintenance are also part of prevention. Cleaning with chemicals suited to the coating system, avoiding leaving chemicals standing on the floor for long, and treating small surface damage early before it spreads into a crack network, will extend the life of the coating. When advice is needed on a coating system suited to a specific area, or a survey of a currently cracking floor is needed, you can contact us via the Kadier contact form.
Note on specifications
Kadier had not published an official technical data sheet (TDS) for its coating systems at the time this article was written. This article therefore presents only a general framework of principles on crow’s-foot cracking in epoxy coatings and gives no specific values for mixing ratio, coat thickness, application temperature or humidity, waiting time between coats, or curing time. Every specific value, when needed for an actual project, must be checked against the official technical documentation of the exact product used, or against the supplier’s written instructions. Do not use the general frameworks in this article as a substitute for the product’s technical documentation.
