7 Common Mistakes in Processing Polyurethane Systems That Cost Time and Money

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Polyurethane systems are among the most versatile materials in industry – from insulating foams and elastomers to coatings. However, their processing demands strict technological discipline. Even minor deviations in component ratios, temperature, or humidity can lead to insufficient strength, uneven structure, or reduced product lifespan. In practice, the same mistakes often recur, costing manufacturers time, raw materials, and money. How can they be identified and eliminated before production begins?

1. Failure to maintain temperature conditions during processing

Polyurethane systems are sensitive to temperature both during storage and processing. The ideal temperature for most two-component PUR systems ranges between 20–25 °C. If the temperature is lower, the reaction between polyol and isocyanate proceeds more slowly, leading to insufficient curing, a sticky surface, or inadequate mechanical strength. Conversely, excessively high temperatures accelerate the reaction to such an extent that premature gelling of the mixture may occur before application, preventing even spreading or injection.

Before processing, it is essential to allow both components and moulds to temper to the required temperature for at least 12–24 hours. Using untempered raw materials results in uneven mixing, bubble formation, or insufficient adhesion to the substrate. For machine processing, it is also important to monitor the temperature of hoses and nozzles to prevent local overheating. In winter months, it is advisable to heat storage areas, while in summer, cooling is recommended to avoid temperature fluctuations.

2. Incorrect Mixing Ratio of Components

Polyurethane systems require precise adherence to the weight or volume ratio between the polyol and isocyanate components. A deviation of even a few percent can significantly affect the properties of the final product—from reduced strength and elasticity to insufficient curing or excessive brittleness. Accurate dosing is therefore crucial, whether for manual mixing or machine application.

When mixing manually, it is essential to use calibrated scales or measuring containers and ensure that residual material in packaging is not neglected. For machine processing, regularly check the calibration of dosing pumps and ensure there is no clogging or leakage. If in doubt, it is advisable to prepare a test mixture and verify its properties before starting serial production. An incorrect ratio often only becomes apparent after curing, when correction is costly or impossible.

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3. Inadequate ventilation and neglect of health protection

Isocyanates, a key component of polyurethane systems, are highly reactive and can pose a health risk if inhaled or upon skin contact. Inadequate ventilation of the workspace leads to the accumulation of vapours, which can cause respiratory irritation, allergic reactions, or even asthma attacks. According to REACH and CLP regulations, the workplace must be equipped with effective extraction systems, and employees must use personal protective equipment such as respirators with appropriate filters, safety goggles, and gloves.

In addition to health risks, poor ventilation can also affect the quality of the processed material. Moisture and dust from the air can enter the mixture, causing bubble formation, reduced adhesion, or uneven curing. Before starting work, it is therefore necessary to check the functionality of the extraction system and ensure that the workspace is clean and dry. When working with larger volumes, it is advisable to use closed systems with local extraction directly at the emission source.

4. Incorrect Storage of Raw Materials and Failure to Observe Expiry Dates

Polyurethane raw materials, especially isocyanates, are sensitive to moisture and temperature fluctuations. Improper storage can lead to material degradation, which manifests as changes in viscosity, reduced reactivity, or the formation of undesirable by-products. Storage areas should be dry, cool (ideally 15–25 °C), and well-ventilated to minimise the risk of moisture condensation on packaging. Containers must be tightly sealed and stored away from direct sunlight.

Another important factor is adhering to expiration dates. Even with proper storage, raw materials gradually degrade, particularly isocyanates, which react with atmospheric moisture. After expiration, the material may become unsuitable for use, which can manifest as prolonged curing time, reduced strength, or increased brittleness. Therefore, it is essential to check the expiration date before use and, in case of doubt, prepare a test mixture. Storing raw materials according to the manufacturer's recommendations is the foundation for achieving consistent results and minimizing losses.

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5. Ignoring moisture and contamination of raw materials

Polyurethane systems are extremely sensitive to moisture, which can cause undesirable reactions even before processing. Water reacts with the isocyanate component to form carbon dioxide, leading to bubble formation in the material, reduced mechanical properties, and in extreme cases, complete degradation of the mixture. Typical symptoms include foaming of the mixture or loss of adhesion to the substrate. Moisture can enter raw materials not only from the surrounding environment but also from insufficiently dried containers, tools, or even contaminated fillers such as pigments or mineral-based fillers.

Prevention involves careful storage of raw materials in hermetically sealed containers with desiccants (e.g., silica gel) and the use of dry tools. Before processing, it is advisable to check the air humidity in the workspace—ideally, it should not exceed 50% relative humidity. For sensitive applications, such as transparent coatings or high-strength foams, it is recommended to filter premixed components through a fine mesh to remove any impurities or precipitates formed by reaction with moisture. It is also important to ensure that raw materials are not stored near water sources or in areas with high condensation.

6. Inadequate Surface Preparation Before Application

Even a well-mixed polyurethane system will fail if the substrate is not properly prepared. Insufficient adhesion to the surface leads to peeling, cracking, or bubble formation, resulting in wasted time and material. Common mistakes include inadequate degreasing of the surface, residues of old coatings, dust, rust, or insufficient roughening of smooth materials such as metals or certain plastics. Polyurethanes require a clean, dry, and mechanically treated substrate to form a strong chemical and mechanical bond.

Surface preparation should begin with thorough cleaning to remove dirt and grease using suitable degreasing agents (e.g., alcohol-based or special industrial cleaners). For metals, it is essential to remove rust and create micro-roughness, ideally through sandblasting or grinding. For plastics, surface activation is often necessary using plasma treatment or special primers that improve wettability. Before applying polyurethane, it is advisable to perform an adhesion test on a small area to verify material compatibility. The additional costs of high-quality surface preparation pay off—poorly prepared substrate may result in the need for a complete rework of the entire application.

7. Exceeding the Processing Time (Pot Life) and Failure to Observe Technological Times

Every polyurethane system has a defined processing time (pot life), during which the mixture must be applied before it begins to lose its properties. Exceeding this time leads to thickening of the mixture, reduced flowability, and ultimately insufficient bonding of components, resulting in weaker mechanical properties, uneven curing, or even complete material failure. It often happens that workers underestimate the time required for application, especially for larger surfaces or complex shapes, and attempt to process the mixture even after the pot life has expired.

The solution is careful planning of the workflow and adjusting the amount of mixed compound to current needs. It is recommended to mix only the quantity that can be processed within 70–80% of the pot life to allow a time buffer for any complications. For systems with a short processing time (e.g., under 10 minutes), it is advisable to use automatic mixing equipment or two-component guns to minimize the risk of errors. It is also important to monitor the ambient temperature—higher temperatures accelerate the reaction and shorten the pot life, while lower temperatures extend it. Always adhere to the technological times specified in the manufacturer’s technical data sheet and adjust the workflow accordingly.

Need to optimize PUR system processing?

Every polyurethane system requires an individual approach – from the correct ratio of components to adherence to technological parameters. GCG Group provides detailed technical data sheets and safety documentation for every supplied raw material, including processing recommendations. Our experts will advise you on selecting the right system for your application and help avoid common mistakes. Contact us – or browse our catalog of over 1,300 products right away.