Whether you're a beginner in fibreglass moulding or an experienced practitioner, encountering issues like patches of wrinkles or gelcoat crinkling on your GRP parts can be frustrating.
There are several factors that can contribute to the problem of wrinkles or crinkling in your gelcoat during fibreglass moulding. Here are some common causes and suggested solutions:
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Thin Gelcoat: If your gelcoat is too thin, it won't be able to resist the styrene present in the resin. In this case, the gelcoat may not cure properly due to a lack of exotherm. When you apply additional layers of resin or gelcoat, the styrene acts as a solvent and starts to attack the first gelcoat layer, similar to how a paint stripper affects paint. To avoid this, ensure that your gelcoat has the appropriate thickness to resist styrene and allow for proper curing.
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Improper Curing Time: If the gelcoat has cured properly, but the resin takes too long to cure due to insufficient catalyst or low working temperatures, a similar issue can occur. It's crucial to maintain an adequate working temperature and condition both the materials and mould to room temperature before starting the lay-up process. Aim for a curing time of around 30 minutes to 1 hour, depending on the specific requirements of your fibreglass.
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Contamination: Sometimes, wrinkles and crinkling can be caused by contamination on the gelcoat surface. This can occur if substances like acetone, styrene, or uncatalyzed resin are spilled onto the gelcoat before lay-up. Take care to avoid any accidental spills or splashes that could compromise the integrity of the gelcoat.
To repair the affected areas:
If the wrinkling is minor and limited to a few areas, you can use a Dremel or detail router with a diamond tip to open up the affected area and create a good surface abrasion. Then, mix a small amount of catalyzed gelcoat and fill the area slightly above the original surface. Allow it to cure overnight until it reaches optimum hardness, and then wet sand and polish it to achieve a smooth finish. Be cautious not to remove too much of the surrounding surface, especially if you suspect the gelcoat is too thin.
If the wrinkling is extensive and spread throughout the project, it may be best to start afresh and discard the current piece.
To prevent this issue in the future, consider the following measures:
- Maintain a working temperature of around 18°C or above.
- Allow the products and moulds to acclimate to the workshop temperature before starting the lay-up process. Avoid laying up late in the afternoon if the temperature is likely to drop before the curing cycle is complete.
- Apply gelcoat with a thickness of approximately 0.6mm, ensuring that no mould is visible through the gelcoat but avoiding excessive thickness that may cause running. You can refer to instructional videos on how to apply gelcoat for guidance.
- Apply a sufficient amount of catalyst to the product being applied to the cured gelcoat, whether it's resin or a second layer of gelcoat.
- Take precautions to prevent any contaminants from entering the mould, such as spills or splashes of other chemicals.
By implementing these measures and techniques, you can minimise the occurrence of gelcoat wrinkles or crinkling and achieve better results in your fibreglass moulding projects.
