Before beginning any GRP work, it is crucial to ensure that your workshop maintains a constant temperature, ideally between 15-20°C. The workspace should be dry, well-ventilated, and organized, with designated areas for reinforcement preparation, resin mixing, molding, and finishing. Avoid exposing molds to direct sunlight. Cleanliness is of utmost importance to ensure operator safety and prevent material contamination.
Personal protective equipment should be worn at all times, including safety spectacles, gloves, aprons, and coveralls. Read and adhere to all hazard labels on containers and on-site. If you have any uncertainties, feel free to contact us at +61 473 243 787.
Here is a guide for laying up fibreglass reinforcement into a pre-prepared mold:
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Apply a layer of catalyzed gelcoat (2-3% by volume) to the mold, aiming for a recommended thickness of 0.4-0.6mm. As a rough estimate, 1kg of gelcoat covers approximately 1.6 square meters. Once the gelcoat reaches a tacky finish that doesn't rub off onto fingers (typically 1-2 hours at room temperature), you can proceed to add layers of glassfibre matting. Keep in mind that even though the gelcoat may seem fully cured, certain corners and crevices may still be wet, so wait for them to dry.
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Prepare all your materials and equipment before starting the lay-up process. To calculate the approximate amount of resin needed, multiply the weight of the chopped strand mat by 2.5. For example, 1kg of matting requires 2.5kg of resin. Only mix the required amount of resin at a time. Using catalyzed resin, wet out the gel-coated area, lay the first sheet of fibreglass matting over it, and use a stippling motion to wet out the layer (avoid painting side to side, as it can cause the fibers to separate). Add more resin if necessary, ensuring the matting is completely saturated. Use a metal paddle roller to remove any trapped air and consolidate the matting onto the gelcoat. Once the first layer is flat and fully laid, repeat the process for subsequent layers. It is not necessary to wait for each layer to cure unless you are applying more than three layers. In such cases, allowing the first layer to cure before adding more prevents heat generation during the curing process, which can lead to pre-releasing and warping of the item.
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While laminating, the resin is already undergoing its curing stage. If the resin starts to thicken and become unworkable, flatten out any matting and clean your tools thoroughly with acetone to prevent premature curing. Mix a fresh batch of resin and continue the process. Be cautious of excess resin in a bucket, as it can emit toxic smoke if it cures. Immediately fill the bucket with cold water and move it to a safe area. Remember that acetone is highly flammable, so avoid smoking near it or exposing it to sparks or flames.
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Once the laminate has cured but is still somewhat green (not too hard), you can trim it using a Stanley knife. If it has fully hardened, use a hacksaw or diamond wheel cutter, ensuring you wear safety gear and a breathing mask when cutting GRP. When removing the laminate from the mold, use wooden or plastic wedges, taking care not to scratch the laminate or the mold. Alternatively, carefully use mole grips and a tire lever, placing the grips above the mold on excess material. If the mold has been properly waxed, the laminate should be easily removed.
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To achieve a high-quality surface coat, it is crucial to apply it in a warm, dry, and well-ventilated environment. The final coat should have a smooth finish, but if desired, it can be further enhanced by using wet and dry paper, followed by polishing with cutting compound and an electrically powered polishing mop.
The curing process for the laminate typically takes around 10-14 days at a temperature of 21ºC. Curing will take longer at lower temperatures, but it is not recommended. The temperature during curing should never drop below 15ºC.
If you plan to work outside, it is essential to schedule your work during a dry period and avoid undertaking it in unsettled weather.
Please note that this advice and information are provided in good faith for guidance purposes only. It is given without warranty, and users should use their own judgment to determine the suitability of the information provided.
Image credit: https://www.resinlibrary.com/wp-content/uploads/2019/11/laminating-with-polyester-resin.jpg
