GRP Over GRP Roofing

Extending or recoating an existing GRP (Glass Reinforced Plastic) roof is possible, but it requires careful consideration and proper techniques. While blending new GRP with an existing roof can be done, it’s crucial to ensure a firm connection between the old and new sections to maintain structural integrity and weather resistance.

Can You Apply GRP Over Existing GRP?

Applying new GRP over an existing GRP roof is possible but requires careful preparation and execution. The existing GRP surface must be thoroughly cleaned, sanded, and any damage repaired before applying new materials. For minor repairs, a fiberglass repair kit can be used to patch small holes or cracks. When recoating, a polyurethane-based restoration coating like GRP Restoration Coating can be applied in a single coat, extending the roof’s lifespan by 10-15 years without the need for complete replacement.

This method is more cost-effective and environmentally friendly than full replacement, provided the existing roof is still in decent condition. However, it’s crucial to ensure proper bonding between old and new sections to maintain structural integrity and weather resistance. For more extensive damage or structural issues, replacement may be necessary rather than recoating.

Techniques for GRP Roof Extension

When extending or recoating a GRP roof, proper preparation and application techniques are crucial for a successful outcome. The existing surface must be thoroughly cleaned and sanded to create a suitable bonding surface. Any damaged areas should be repaired before applying new materials. For minor repairs, a fiberglass repair kit can be used to patch small holes or cracks.

When applying new GRP, it’s essential to maintain the correct ratio of resin to glass matting, typically 3:1 (1.5kg resin to 0.45kg chopped strand mat). The resin should be mixed with the appropriate amount of catalyst based on ambient temperature to ensure proper curing. Careful attention to detail during application, including proper wetting out of the matting and use of a paddle roller to remove air bubbles, will help ensure a durable and watertight finish.

Bonding GRP to Lead and Concrete

Bonding GRP to lead and concrete requires specific preparation and techniques to ensure proper adhesion. For concrete surfaces, thorough cleaning and priming are essential, for further anti-slip solutions click here. A PU adhesive paste can be used to create a strong, water-resistant bond between GRP and concrete. When applying GRP to concrete, it’s crucial to use a concrete primer, such as Cure It GRP Roofing G4 Concrete Primer, which promotes enhanced bonding characteristics. The concrete surface should be clean, dry, and well-prepared before applying the primer.

For lead surfaces, careful surface preparation is also necessary. Some installers recommend fixing 11mm OSB to the concrete structure before applying the GRP system, as this can provide better adhesion. Regardless of the substrate, proper surface preparation and the use of appropriate primers and adhesives are key to achieving a durable and watertight GRP installation on lead or concrete surfaces.

Recoating vs. Replacing GRP Roofs

Recoating a fibreglass (GRP) roof is often a viable and cost-effective alternative to full replacement, especially if the existing roof is still in decent condition. Recoating can effectively restore the look of a GRP roof and address issues like small cracks or pinholes without the need for complete replacement. A polyurethane-based restoration coating, such as GRP Restoration Coating, can be applied in a single coat to rejuvenate the roof, extending its lifespan by 10 to 15 years.

This method is not only more economical but also more environmentally friendly as it eliminates the need to remove the old membrane. However, for roofs with significant damage or structural issues, replacement may be necessary. When considering recoating versus replacing, factors such as the roof’s age, extent of damage, and long-term cost-effectiveness should be carefully evaluated.

Integrating Skylights in GRP Roofs

When installing skylights or roof windows in a GRP roof, it’s important to ensure proper integration to maintain the roof’s watertight integrity. The skylight frame and kerb should be installed before applying the GRP laminate and topcoat. This allows the GRP to be laid up to and over the kerb, creating a seamless, weatherproof seal.

Once the frame and kerb are in place, the surrounding area should be sanded to provide a good key for the GRP laminate. The laminate can then be applied, overlapping the kerb and frame to ensure a watertight bond. After the laminate has cured, the topcoat can be applied, further sealing the skylight into the roof.

It’s generally not recommended to cut openings for skylights after the GRP roof has been fully installed, as this can compromise the roof’s integrity. However, if necessary, the topcoat around the new opening must be sanded back thoroughly and cleaned with acetone before installing the skylight and resealing with GRP. Proper planning, correct sequencing of installation steps, and attention to detail are crucial when integrating skylights into a GRP roof to ensure a durable, leak-free result.

Adhesive Selection for GRP Bonding

When selecting adhesives for GRP bonding, particularly for roofing applications, several specialized options are available. Universal GRP Trim Adhesive, a one-component, moisture-curing polyurethane sealant and adhesive, is widely used for bonding GRP trims. This high-modulus adhesive offers excellent adhesion to most building substrates, fast curing, and durable elasticity.

For bonding GRP to materials like lead or concrete, Matrix Trim Adhesive is recommended. It provides a flexible joint that can accommodate the different thermal expansion rates between materials. When working with concrete, G4 Dampseal can be used as a primer to facilitate adhesion. For bituminous surfaces, G4 can neutralize small areas, although overboarding with OSB3 Sterling is generally preferred.

These specialized adhesives ensure strong, weather-resistant bonds in GRP roofing applications, contributing to the overall durability and longevity of the roofing system.

In conclusion 

 Extending, recoating, or integrating new elements into a GRP (Glass Reinforced Plastic) roof is a viable and cost-effective approach when done with proper preparation and techniques. Whether applying new GRP over existing material, bonding GRP to other surfaces like concrete or lead, or installing skylights, attention to detail and the right materials are essential for maintaining the roof’s structural integrity and weather resistance. Recoating can extend the life of a GRP roof by 10-15 years, making it an environmentally friendly and economical alternative to full replacement, provided the existing roof is in good condition. With careful planning and execution, GRP roofing systems can be successfully upgraded and maintained for long-term durability.