Which Resin Is Best for Metal and Fibreglass RV Roof Seams?

Why polyester resin is the better option for rigid seams

Polyester resin is widely used for laminating and structural repair because it cures hard and bonds well to prepared fibreglass, aluminium and steel. When paired with a fibreglass mat, it creates a reinforced bridge across the seam that spreads stress rather than concentrating it in one line. This is important on an RV roof, where cyclic movement and road vibration can cause flexible sealants to pull away.

A complete kit such as the Resin Fibreglass Repair Kit – Complete Polyester Resin and Hardener Set includes the resin, hardener, mat and basic tools, so you are not mixing separate components from different systems.

Preparation and application sequence

Start with a dry, grease-free surface. Lightly sand or abrade the metal and fibreglass around the seam so the resin has a mechanical key, then wipe away dust. Cut the fibreglass mat into manageable strips that overlap the seam by a few centimetres on each side.

• Mix the polyester resin and hardener at the ratio given in the kit instructions.
• Apply a thin resin coat to the prepared seam, lay the mat onto the wet resin, then stipple more resin through the mat until it becomes translucent.
• Add a second layer if the seam is wide or the roof skin is thin, and let it cure fully before sanding or painting.

When this matters: metal-to-fibreglass transitions

This approach matters most where the roof sheet overlaps a fibreglass end cap, or where a previous lap sealant has cracked and allowed water beneath the surface. In those areas, a polyester and fibreglass laminate can span the joint and rebuild stiffness rather than simply covering the crack. If the surrounding panel is badly corroded or flexes heavily, fill deep voids first and consider whether the repair needs additional mechanical support before laminating.