Step-by-Step: Installing the TriRoof Complete GRP Roofing System

Flat Roof Installation

Installing a flat roof doesn’t have to be complicated. In fact, it becomes much simpler—especially when you’re working with a high-performance system like TriRoof GRP from Tricel Composites. Not only is it designed for durability, ease of use, and long-term protection, but the TriRoof Complete GRP System is also ideal for both professionals and trained DIYers. In this guide, we’ll walk you through the full installation process, from surface preparation to final topcoat, so you can achieve a flawless, watertight finish every time.

What You'll Need

Before you begin, make sure you have the following tools and materials:

Tools:

  • Paddle roller
  • Laminating brush
  • Mixing buckets
  • Scissors or shears
  • Acetone (for cleaning tools)
  • Protective gloves and eyewear

Materials:

  • TriRoof Resin
  • TriRoof Topcoat
  • TriRoof Fibreglass Matting (typically 450g/m²)
  • TriRoof Primer (if required)
  • OSB3 decking (if replacing the roof deck)

Step 1: Prepare the Roof Deck

To begin with, a solid, clean, and dry substrate is essential for a successful GRP installation.

  • To start, ensure the roof deck is made from OSB3 tongue-and-groove boards, securely fixed with no movement.
  • After securing the deck, remove any dust, debris, or moisture to ensure a clean working surface.
  • Additionally, check for any sharp edges or protrusions that could damage the fibreglass matting.

Tip: Alternatively, if overlaying an existing roof, use TriRoof HPX or MultiFlex instead of the standard GRP system.

Step 2: Install Edge Trims

To ensure proper drainage and a clean finish, TriRoof edge trims are essential for directing water flow and creating a neat appearance.

  • Additionally, check for any sharp edges or protrusions that could damage the fibreglass matting.
  • Therefore, ensure corners are mitred and sealed with resin to prevent leaks.
  • Additionally, use expansion joints if the roof exceeds 50 m².

Step 3: Prime the Surface (If Required)

To improve adhesion, especially if the surface is porous or dusty, apply TriRoof Primer before proceeding.

  • Next apply with a roller or brush.
  • Then, allow to dry fully before proceeding.

Step 4: Cut and Position the Fibreglass Matting

  • First, pre-cut the fibreglass matting to fit the roof area, allowing for overlaps of at least 50mm.
  • Next, lay the matting loosely in position to check fit and alignment.
  • Then, roll back sections to prepare for resin application.

Step 5: Mix and Apply the Resin

  • First, mix TriRoof Resin with the correct amount of catalyst (refer to product datasheet for ratios based on temperature).
  • Then, apply resin to the deck using a roller.
  • Immediately after, lay the fibreglass matting into the wet resin.
  • Next, use a paddle roller to remove air bubbles and ensure full saturation.
  • Finally, repeat in sections until the entire roof is covered.

Safety Note: To stay safe during the process, always wear gloves and work in a well-ventilated area when handling resin.

Step 6: Allow to Cure

  • Let the resin cure fully—typically 1–2 hours depending on temperature.
  • The surface should be tack-free before applying the topcoat.

Step 7: Apply the Topcoat

  • Mix the TriRoof Topcoat with catalyst.
  • Apply evenly across the entire surface using a roller or brush.
  • Make sure the entire surface is coated evenly, paying extra attention to edges and trims.
  • Allow to cure for at least 24 hours before walking on the roof.

Step 8: Final Inspection and Clean-Up

  • Next, check for any missed areas or imperfections.
  • Then, clean tools with acetone before the resin cures.
  • Finally, dispose of waste materials responsibly.

Conclusion: A Professional Finish, Every Time

As a result, the TriRoof Complete GRP System is designed to make flat roofing straightforward and reliable. Therefore, with the right preparation and attention to detail, you can achieve a seamless, watertight finish that lasts for decades.

Need Training or Support

For further support, contact Tricel Composites to learn more about CPD-accredited installer courses, technical advice, and product availability.

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April 12, 2025