Fibreglass — or glass-reinforced plastic (GRP) — is used in many baths, shower trays, shower enclosures and wet room panels, particularly in corner bath shapes, larger baths and bespoke bath designs where fibreglass’s mouldability allows shapes that acrylic cannot easily achieve. Fibreglass can crack, chip, blister and delaminate over time, particularly in older installations. Professional surface repair can address most fibreglass damage effectively.
How to Identify Fibreglass (GRP)
If you are unsure whether your bath or shower tray is acrylic or fibreglass, there are a few indicators. Fibreglass is typically heavier and stiffer than acrylic — pressing on the surface doesn’t give the same slight flex that acrylic does. Damaged fibreglass often shows a characteristic chalky-white appearance in chips and cracks as the gel coat surface separates from the underlying glass fibre structure. Older baths — pre-1990s — are more likely to be fibreglass or enamelled cast iron than modern acrylic.
Gel Coat Damage
The visible surface of a fibreglass bath or shower tray is the gel coat — a polyester resin layer applied to the mould before the fibreglass layers are built up behind it. Most chips and surface damage in fibreglass affects this gel coat layer. Gel coat repairs use colour-matched polyester repair compounds that bond to the existing gel coat and can be finished and polished to a gloss surface matching the original appearance.
Structural Cracks in GRP
Cracks that penetrate through the gel coat into the fibreglass layers beneath indicate structural damage rather than surface damage. These can result from impact, substrate failure (flex in the floor beneath the shower tray), or progressive cracking from repeated loading over time. Structural cracks require repair from both sides where possible — the outer gel coat is repaired and refinished, while the inner fibreglass structure is reinforced with additional GRP laminate applied from inside.
Fibreglass Delamination and Blistering
Blistering in fibreglass — where bubbles or raised areas appear in the surface — is often caused by osmotic moisture absorption over many years, or by air voids in the original laminate. Small blisters can be ground out, dried, and refilled with gel coat compound. Extensive blistering across large areas may indicate the end of the usable life of the fibreglass installation.
Colour Fading in Old Fibreglass
Older fibreglass baths — particularly those in period colours like avocado, harvest gold, burgundy or shell pink — can fade and chalk over time as the gel coat breaks down. Full surface refinishing with a new applied coat can restore the appearance and colour of a faded fibreglass bath, giving it a fresh lease of life without replacement.
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