Is the Resin Fibreglass Repair Kit Truly Waterproof?

How the waterproofing actually works

Once mixed at the 3% hardener ratio, the orthophthalic polyester resin cures into a solid, non-porous layer. Rather than sitting on the surface like a paint film, the resin soaks into the fibreglass mat and bonds to the prepared substrate, creating a continuous repair patch. This is different from a simple sealant because the cured resin itself blocks water penetration and gives the repair structure.

For a van roof, that means the patch can handle standing water and heavy rain as long as the area around the repair is sound. It is not a flexible membrane, so the repair works best on rigid panels rather than surfaces that move or flex significantly.

Durability and outdoor performance

The cured repair is impact-resistant and intended for outdoor exposure, making it suitable for areas that face weather, temperature changes and general road use. The included mat helps spread stress across the repair, reducing the chance of localised cracking. That said, polyester resin benefits from being kept clean and inspected periodically, especially where the original surface was badly damaged.

If you want additional UV and abrasion protection, a compatible topcoat such as Prolux PU coating can be applied over a properly prepared polyester repair. This is particularly useful on visible roof areas exposed to sunlight and regular washing.

When this matters for van roofing

Waterproof durability becomes critical when a roof repair sits above a living space, electrical equipment or insulation. A slow leak can cause staining, rot or corrosion that is more expensive to fix than the original crack. This is where a structural fibreglass patch can outperform a temporary tape or mastic repair, because it restores strength and blocks water at the same time.

• Rigid roofs: fibreglass, metal and well-supported wood panels are usually good candidates.
• Sealed edges: make sure surrounding seams and fixings are clean and dry before laminating.
• Topcoats: add a UV-resistant coating if the repair will be directly exposed to sunlight for long periods.