Défauts courants du gelcoat

Lorsqu'ils sont utilisés correctement, les gelcoats offrent une finition durable et fiable. Voici quelques raisons courantes qui expliquent pourquoi certains défauts peuvent se produire :

Understanding Gelcoats and Their Role

Gelcoat is the outermost resin layer applied to many composite parts, providing both a smooth, glossy surface and essential protection. It enhances the visual appearance of the part by hiding the underlying fibre-reinforced laminate, while also offering UV resistance to prevent yellowing, chalking, or degradation from sunlight exposure. In addition, gelcoat acts as a barrier against moisture, chemicals, and environmental wear, helping to preserve the structural integrity and long-term performance of the composite.

There are several methods for applying gelcoat, each suited to different production needs. Spray application is commonly used for large or complex moulds, with both dry and wet spray techniques available; products like Scott Bader’s Crystic Spray Gelcoat Stonecast 95PA are specifically formulated for this method. Brush application is ideal for smaller parts, touch-ups, or areas that are difficult to reach with a spray, and requires proper stirring and quality brushes to avoid defects. Specialised tooling spray setups, such as airless or pot spray guns, offer precise control over nozzle size, pressure, and spray distance for detailed applications.

Correct application technique is critical to achieving a high-quality finish and maintaining gelcoat performance. Factors such as mixing, coating thickness, number of coats, catalyst levels, and curing conditions directly affect outcomes; improper handling can lead to surface defects, peeling, delamination, or reduced resistance to UV and moisture. Using a reputable supplier ensures consistent quality, correct resin formulation, appropriate additives, and access to technical support. Scott Bader’s Crystic and Crestamould ranges exemplify how reliable materials and guidance contribute to durability, gloss retention, and long-term performance.

Common Gelcoat Faults and Their Causes

Porosity

Porosity appears as small pinholes or bubbles on the gelcoat surface, compromising both appearance and durability. It is commonly caused by air entrapment during application, spraying from an incorrect distance, or using gelcoat with too high a viscosity. To prevent porosity, it is important to maintain proper spray technique, control the resin’s viscosity, and ensure adequate degassing or rolling out of trapped air during application.

Cracking and Crazing

Cracks or fine lines (crazing) on the gelcoat can reduce both structural integrity and visual quality over time. These defects often result from excessive gelcoat thickness, rapid temperature changes, or uneven curing. Best practices to avoid cracking include applying the correct coat thickness, controlling curing conditions, and allowing gradual temperature changes during the curing process.

Wrinkling

Wrinkling manifests as surface ripples or uneven texture, usually beginning in localized areas before spreading. This is often caused by poor adhesion between layers, surface contamination, or solvent attack from improper resin formulations. Preventive measures include careful surface preparation, ensuring full curing of underlying layers, and avoiding contaminants during application.

Blisters

Blisters are raised pockets on the gelcoat surface, typically caused by trapped air or moisture, incomplete curing, or incorrect application. They are closely related to poor gelcoat techniques such as applying too thick a layer or failing to allow proper degassing. Repair involves removing the affected area and reapplying gelcoat correctly, while prevention relies on proper application technique, correct thickness, and environmental control during curing.

Colour Variations and Fading

Colour consistency is critical for aesthetic quality and is influenced by correct pigment mixing and high-quality resin supplied by reputable manufacturers. Over time, UV exposure can cause fading, chalking, or uneven colour. Minimising these effects requires proper pigment dispersion, using UV-stabilised gelcoats, and selecting products from trusted suppliers to ensure consistent performance.

The Importance of Quality Gelcoat Application

Skilled gelcoat application is essential for achieving high-quality composite finishes while minimizing rework and material waste. Properly trained operators can apply the correct thickness evenly, avoid defects such as porosity or wrinkling, and ensure that the gelcoat cures correctly, saving both time and resources. Equipment setup and environmental controls—such as correct spray pressure, nozzle selection, temperature, and humidity—play a critical role in maintaining consistent results. Alongside technical precision, training and experience are vital, as they enable applicators to anticipate potential issues, adjust techniques on the fly, and consistently produce durable, visually appealing surfaces.

Repairing Gelcoat Issues

When defects occur, timely and proper repair is crucial to restore both appearance and performance. Common repair methods include sanding out minor surface imperfections, filling pinholes or cracks with compatible gelcoat or putty, and reapplying a thin layer of gelcoat followed by careful finishing. For more complex repairs or guidance on selecting the right products, detailed technical guides and product recommendations from reputable suppliers such as Scott Bader provide step-by-step instructions and best practices to ensure long-lasting results.

Choosing the Right Gelcoat Supplier

Selecting a reliable gelcoat supplier is crucial, as consistent product quality directly affects the performance, durability, and appearance of composite parts. Scott Bader, for example, offers a wide range of high-quality gelcoats with proven consistency, backed by technical support and comprehensive product assurances. Working with a reputable supplier ensures access to expert guidance, datasheets, and troubleshooting advice, helping manufacturers avoid common faults. When evaluating a supplier, key questions include asking about resin formulation, UV stabilisation, recommended application techniques, quality control measures, and after-sales support to ensure the gelcoat meets both production and long-term performance requirements.

Understanding and preventing gelcoat faults is essential for achieving durable, high-quality composite finishes while minimising rework and material waste. By familiarising yourself with common issues such as porosity, cracking, wrinkling, blisters, and colour variation, and following best practices for application, you can ensure long-lasting performance and superior aesthetics.

For a quick visual reference, download or print our infographic summarising key gelcoat faults and prevention tips.

To take the next step, contact us for expert advice on gelcoat application or browse our professional-grade gelcoat products to find the right solution for your needs.