How to repair a fibreglass flat roof

GRP fibreglass roofs are tough, long-lasting, and one of the most reliable flat roofing systems used in the UK.

But like anything exposed to weather year after year, even a fibreglass roof can develop cracks, pinholes, or small areas of blistering.

If you’re searching

“how to repair a fibreglass flat roof?”

Here’s the truth:

✔ Small GRP roof issues can be repaired

✘ Bigger cracks or structural problems shouldn’t be DIYed

✔ A proper GRP repair requires resin, matting, sanding, and a new topcoat

✘ A quick patch or silicone sealant will NOT last

Let’s break down the right way to do it.

*Identify the Problem on the GRP Roof

Before repairing anything, you need to know what type of damage you’re dealing with.

GRP roofs typically suffer from:

🔹 Small Cracks

Hairline cracks caused by weather changes.

🔹 Pinholes

Tiny holes that let water seep in slowly.

🔹 Blistering / Bubbles

From trapped air or poor installation.

🔹 Worn Topcoat

The shiny finish becomes chalky or thin.

🔹 Edge Cracks

Weak spots where trims meet the main roof.

Each problem needs a different repair method.

*Clean and Prepare the Area

GRP repairs only stick properly to clean, dry, dust-free surfaces.

You must:

✔ Clean the damaged area

✔ Remove dirt, moss, and debris

✔ Dry the roof properly

✔ Lightly sand the surface so the resin can bond

If moisture is trapped under the surface, the repair won’t last.

Requires resin, matting, sanding, and topcoat.

*Repairing Small Cracks or Pinholes

For tiny cracks or pinholes:

Step-by-step:

1.Sand the damaged area

2.Clean with acetone

3.Apply fresh GRP resin

4.Allow it to cure

5.Apply a finishing topcoat

This seals the crack completely and restores waterproofing.

*Repairing Larger Cracks or Blistering

Bigger damage requires reinforcement.

Step-by-step:

1.Sand the area until the weak section is removed

2.Cut a piece of fibreglass matting

3.Apply a layer of resin

4.Roll the matting into place

5.Add another coat of resin

6.Leave to cure

7.Sand again

8.Apply a new GRP topcoat for a uniform finish

This restores the strength of the fibreglass.

*Repairing Worn or Damaged Topcoat

If your GRP roof is faded, chalky, or slightly porous:

✔ Sand the entire roof

✔ Clean thoroughly

✔ Apply a fresh topcoat

This is usually enough to restore waterproofing for years.

*When NOT to Repair a GRP Roof Yourself

Some problems require a professional roofer:

✘ Large cracks across the roof

✘ Soft or rotten decking underneath

✘ Multiple blistering patches

✘ Flashing or trim failures

✘ Water trapped under the laminate

These issues mean the roof needs a proper GRP restoration, not just a small patch.

How Much Does a Fibreglass Roof Repair Cost?

💷 GRP Fibreglass Roof Repairs:

£120 – £350 for most repairs

Up to £500 for larger sections

This includes:

•Resin repairs

•Matting reinforcement

•Topcoat restoration

*How Long Does a GRP Roof Last?

A properly installed GRP roof lasts:

👉 25+ years

And even longer with regular topcoat maintenance.

Should You Repair or Replace Your GRP Roof?

You should replace if:

•The roof is 20–25+ years old

•Multiple areas are failing

•The deck beneath is damaged

•Leaks keep coming back

You should repair if:

•The damage is small and localised

•The roof is structurally sound

•The topcoat is worn but the fibreglass is intact

Need a GRP Flat Roof Repair?

Correct Way Roofing specialises in GRP repairs across Telford and surrounding areas.

We offer:

✔ GRP resin and matting repairs

✔ Full topcoat restoration

✔ Crack and blister repairs

✔ Free inspections

✔ Guaranteed workmanship

✔ Max repair price £500

✔ Family-run, local experts

📞 Call Correct Way Roofing for a free on-site inspection and honest price estimate.

Call Us Today