Fibre reinforced plastic (FRP), also known as glass reinforced plastic (GRP), needs to be coated, then the appropriate coating material must be selected and the FRP surface properly treated to ensure long-term performance.
Application of fiber reinforced plastics (FRP)
FRP is often used in highly corrosive exposure environments because it is inherently resistant to corrosion and does not rust like steel. So why cover it with a protective coating? One of the main reasons is to provide UV protection. Exposure to UV light breaks the carbon chains of the polymer, which degrades the resin at the molecular level. An analogy for degradation is the pulverization of an epoxy coating exposed to sunlight. In the case of FRP, with the continuous degradation of the outer layer, the glass fiber will be exposed and the mechanical properties of the laminate will be reduced. If the surface degrades due to ultraviolet light, we can apply a new coating to prevent further degradation.The FRP is coated to match the colour coding of the facility. Many large industrial facilities have specific color codes for their equipment and pipes, such as red for firefighting systems, blue for cooling water and yellow for natural gas. The FRP can be easily painted to meet the colour scheme of the facility.
Fiberglass also needs to be painted for aesthetics. Over time, FRP will fade and the gloss will decrease. If required, the coating will give the component a completely new look, including a high gloss.
FRP is used with different coatings
FRP can be used in a variety of general paint types. Select a specific coating system based on the expected environmental exposure, such as chemicals or ultraviolet light. The following are several types of coatings commonly used in FRP:
Gel layer - Gel coating is commonly used in the manufacturing process. It is a topcoat chosen from the same base resin type used in the manufacture of the product, with the addition of additional UV stabilizers and pigments. There is no reinforced fiber material in the coating and it does not provide structural properties to the assembly. Prior to injection of FRP material, a gel layer can be applied to the surface of the mold or to the surface of the finished product by spraying, brushing or roller coating. Examples include exterior fiberglass panels and pleasure boats that use UV-stabilized gel layers.
Several water-based acrylic coating systems are also available for FRP. Acrylic paint is a single component, easy to apply, construction does not need to add organic solvents other than water. They contain almost no volatile organic compounds (VOC) and are ideal for use in areas with strict restrictions on VOC emissions. Uv resistance, color retention, and powder resistance are generally good, but may vary from product to product. For exposure to harsher working environments (chemical/Marine), better performance coating systems are recommended. Depending on the type of paint, a bonded primer may be required. For specific product requirements, consult the paint manufacturer and consult the product data sheet.
Epoxy systems typically have excellent chemical resistance and are often used in situations where chemical exposure is expected. Epoxy resins are a two-component curing system and need to be mixed before use. Although water-based epoxies can be used, solvent-based epoxies are more common. In general, epoxy resins have poor UV resistance and will whiten and fade in sunlight. If the expected exposure environment is likely to be sun exposure, the epoxy coating should be topped with a finish such as polyurethane.
Polyurethane coatings consist of two components and usually have good chemical resistance. Different from epoxy resin, polyurethane has excellent UV resistance and is suitable for outdoor use. They can be used as an epoxy topcoat or applied directly to the FRP.
How to measure the thickness of FRP coating
Since it is non-metallic material, we can use ultrasonic thickness meter when measuring its total thickness. The thickness measured by the instrument can judge whether the engineering anti-corrosion requirements meet the standards and the FRP coating is corroded.
Sum up
The FRP coating can improve UV and chemical resistance, match color coding regulations for pipes and containers, or improve aesthetics. Traditional industrial coatings, such as acrylic, epoxy, and polyurethane, can be used for FRP coatings. Before coating, the surface must be cleaned, prepared, dried and coarsened to ensure good adhesion.
