Looks Can Be Deceiving: The Hidden Dangers of GRP Sheeting on Timber Bridge Decks

At Bison Bridges, we take safety seriously — not just in the structures we build, but in how they perform over time. A recent incident in West Lothian, where a horse and rider fell through a bridge after a concealed failure beneath a GRP (Glass Reinforced Plastic) surface, has brought a critical issue back into focus.

While GRP sheeting can seem like a quick-fix or protective layer for older timber bridges, it can actually mask serious structural risks. Here’s why that matters more than ever.

The Problem with Hidden Timber Decay

Timber is a versatile and widely used material in bridge construction, but over time, exposure to moisture, weathering, and lack of maintenance can cause rot or internal decay. When timber begins to fail, it may lose strength invisibly — with no obvious external signs.

When a GRP sheet is fixed over a timber deck:

• It covers the wood beneath
• It creates a false sense of surface integrity
• It can even trap moisture, accelerating the rot process

This makes it difficult for inspectors, maintenance teams, or users (especially equestrians or walkers) to spot danger until it’s too late.

Why GRP Alone Isn’t Enough

While GRP offers benefits like grip, weather resistance, and a lightweight surface, it is not a structural solution. It is only as reliable as the substrate beneath it. If the timber has degraded, a GRP cover will not prevent collapse — it may actually delay the discovery of a serious issue.

Real-World Consequences

In the West Lothian case, what appeared to be a safe bridge gave way suddenly, causing a horse and rider to fall through the deck. The outcome could have been tragic. Thankfully, both survived — but it highlights the urgent need for regular inspections and structural transparency.

What Can Be Done?

At Bison Bridges, we recommend the following:

✅ Regular structural inspections – especially on timber bridges with surface coverings
✅ Non-destructive testing methods to assess the condition of the underlying timber
✅ Use of structural-grade, long-lasting decking materials that do not conceal decay
✅ Transparent maintenance logs and routine risk assessments for equestrian and pedestrian routes

If a GRP surface is in place, it’s critical that bridge owners understand what lies beneath — and ensure its structurally sound.

Looking to upgrade or assess your bridge safely? We provide advice on materials that balance grip, visibility, and strength.

Contact the team now on 01530 242405

Let’s make every bridge a safe one — from the surface down!