How We Solved the Problem of Insufficient Adhesion of Polyurethane Coatings on Concrete Floors: A Practical Case from an Industrial Hall

Photo: Craftsman Concrete Floors / Unsplash

Polyurethane coatings are popular in industrial operations for their chemical resistance, mechanical strength, and easy maintenance. However, manufacturers and application technicians often encounter the problem of insufficient adhesion to the concrete substrate, leading to peeling, blistering, or premature wear. In this article, we examine a specific practical case where, in collaboration with a client from a logistics center, we identified the causes of failure and proposed a solution that ensured the long-term stability of the coating. The issue was not in the PUR system itself, but in the substrate preparation and application conditions.

Problem: Why polyurethane coatings lost adhesion to the concrete substrate

Insufficient adhesion of polyurethane (PUR) coatings on concrete floors is a common problem in industrial operations, where floors are exposed to mechanical stress, chemicals, or high humidity. In this particular case, a customer from a manufacturing plant faced peeling of the coating after just a few months of operation, despite using a high-quality two-component PUR system. There were several causes: inadequate surface preparation, residual moisture in the concrete, and a mismatch between the chemical composition of the coating and the floor's surface treatment.

Concrete substrate is a porous material that can retain moisture long after construction is completed. If moisture exceeds the critical threshold (usually 4–5 % by weight for standard PUR coatings), it gradually releases and disrupts the adhesive layer. Another factor was insufficient surface roughness – smooth concrete does not provide adequate mechanical anchoring for the coating. Lastly, contamination of the substrate with oils, grease, or residues of old coatings that were not properly removed may also have played a role.

Diagnostics: How we identified the causes of coating failure

The first step toward a solution was a detailed assessment of the floor's condition and an analysis of the conditions under which the problem occurred. Using standard testing methods, we measured the moisture content of the concrete – the results showed values around 6 %, which significantly exceeded the recommended maximum for PUR coatings. We also conducted an adhesion test using a pull-off test, which confirmed weak bonding between the coating and the substrate. Microscopic analysis revealed the presence of microcracks and impurities at the interface of the two layers.

The key finding was that the concrete substrate had not undergone mechanical abrasive blasting prior to coating application, which would have ensured sufficient surface roughness. Instead, it was only brushed and vacuumed, which was insufficient to remove the weak surface layer (so-called cement laitance). Furthermore, we found that optimal temperature conditions were not maintained during coating application—the substrate temperature was below 10 °C, which slowed curing and reduced adhesion.

Photo: Craftsman Concrete Floors / Unsplash

Solution: How we adjusted the preparation and application technology

Based on the diagnostics, we proposed a comprehensive procedure that included both substrate preparation and optimization of the coating system itself. The first step involved mechanical abrasive blasting of the concrete surface with steel grit, which removed the weak surface layer and created a rough profile with an unevenness depth of approximately 0.5 mm. Subsequently, we dried the substrate using industrial heaters until the moisture content dropped below 4%. Residual dust and impurities were removed with an industrial vacuum cleaner equipped with a HEPA filter.

For the coating itself, we selected a modified PUR system with enhanced moisture resistance and improved adhesive properties. Prior to application, we treated the substrate with an epoxy resin-based primer, which ensured deeper penetration into the concrete pores and created a stable intermediate layer. The coating was applied in two layers with a total thickness of 300–400 μm, while maintaining a temperature range of 15–25 °C and relative humidity below 65%. A technological pause of 12 hours was observed between the individual layers.

Result: Long-term durability and customer satisfaction

After completing the work and curing the coating, we conducted adhesion control tests, which confirmed a significant improvement—the pull-off strength reached values exceeding 2.5 MPa, which is more than sufficient for industrial floors. The coating exhibited a uniform structure without bubbles or cracks and was fully resistant to chemicals used in the operation (oils, solvents, cleaning agents). After one year of operation, there was no peeling or damage, confirming the correctness of the chosen solution.

The customer appreciated not only the technical aspect of the solution but also the comprehensive approach—from diagnostics through technology adjustment to training their own personnel. A key success factor was the combination of proper substrate preparation, selection of the appropriate coating system, and adherence to technological conditions during application. This case demonstrates how important it is to approach industrial coatings as a systemic solution, where each step influences the final result.

Photo: Craftsman Concrete Floors / Unsplash

Choosing the Right Type of Polyurethane System for Concrete Floors

Polyurethane coatings are often chosen for concrete floors in industrial operations due to their high resistance to chemicals, mechanical stress, and abrasion. However, not all PUR systems are equally suitable for this purpose. A key factor is flexibility and the ability to accommodate substrate movements, which concrete exhibits due to temperature changes or vibrations. In our case, we found that the originally used rigid polyurethane system was unable to absorb these microscopic movements, leading to cracks and subsequent loss of adhesion.

For concrete floors, elastic or semi-elastic PUR systems, which combine strength with a certain degree of flexibility, have proven particularly effective. It is also important to consider environmental conditions—such as humidity or temperature during application. In industrial halls, where temperature fluctuations or high loads occur, it is advisable to choose a system with higher resistance to thermal shocks and mechanical stress. The correct choice of PUR system can significantly extend the coating's lifespan and eliminate adhesion issues.

Preparation of the concrete substrate: A step that must not be underestimated

Even the highest-quality polyurethane coating will fail if the concrete substrate is not properly prepared. In our case, one of the main causes of insufficient adhesion was inadequate surface cleanliness and roughness. The concrete must be free of dust, grease, remnants of old coatings, and other contaminants that prevent a perfect bond with the PUR system. Mechanical methods such as sandblasting or grinding are commonly used for this purpose, as they simultaneously increase surface roughness and improve mechanical adhesion.

Another critical factor is the moisture content of the substrate. The concrete must be sufficiently dry, as the presence of moisture can cause blistering or delamination of the coating. Moisture is measured using standard methods, and its value should not exceed the recommended limits specified by the PUR system manufacturer. In some cases, it is necessary to apply a penetrating coat or primer to improve adhesion and simultaneously seal the concrete surface. Without these steps, the risk of coating failure is high, even when using high-quality materials.

Application Conditions and Their Impact on Coating Quality

The quality of a polyurethane coating is not determined solely by the choice of material and substrate preparation but also by the conditions during application. Air temperature and humidity, as well as substrate temperature, play a crucial role. In this case, the application was carried out at a substrate temperature below 10 °C, which slowed the chemical reaction of the PUR system and led to insufficient curing. The result was reduced adhesion and mechanical strength of the coating.

The ideal temperature for applying PUR systems typically ranges between 15 and 25 °C, with the substrate being at least 3 °C warmer than the dew point to prevent moisture condensation. Air humidity should not exceed 80 %; otherwise, there is a risk of blistering or a dull surface finish. In industrial environments where optimal conditions cannot always be maintained, special additives or systems with extended pot life can be used to enable application at lower temperatures. Adhering to these parameters is key to achieving long-term durability and reliability of the coating.

Need a Custom Solution?

Every PUR system requires an individual approach to substrate preparation and application conditions. GCG Group provides detailed technical data sheets and safety documentation for each raw material. Additionally, we will advise you on selecting the right additives and procedures for your specific application. Contact us – or browse our catalog of over 1,300 products right away.