Glass fibre linings

Understanding GRP linings (also known as glass fibre linings)

Protect the surfaces of your buildings and equipment, from chemical bunds, factory floors & walls, to concrete structures and steel supports. Save money by extending the lifetime of your surface.


Glass fibre is a composite, a mixture of resin-based polymer and glass fibre mat. This composite can be used to protect a variety of surfaces, from concrete through to steel wood and existing glass fibre (GRP).

Note: the term “glass fibre lining” also refers to “glass fibre coating” throughout. Likewise, glass fibre is also commonly known as GRP (glass reinforced plastic/polyester) and fibreglass.

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You can find more about Strandek® glass fibre linings and their applications here


Glass fibre linings are lightweight and extremely strong - possessing a very high strength to weight ratio, which exceeds that of certain metals. It is not as brittle as carbon fibre, notably cheaper and has greater flexibility and impact absorption capacity, making it less prone to damage. It is also waterproof and resistant to a wide variety of chemicals, from acid to detergents. These attributes have made it hugely popular with many industries from aerospace through to construction, chemical, space and military sectors.

GRP lining for Grade 1 listed monument, Cardiff, South Wales


Glass fibre lining systems are hugely versatile and durable material perfect for coating a variety of surfaces including but not limited to metals (particularly steel and aluminium), concrete and bricks, wood, as well as glass fibre/GRP surfaces.

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During preparation, the resin, a liquid-based polymer such as unsaturated polyester usually with styrene is used to saturate strands of glass fibre mat, removing air pockets encapsulating glass fibres. This forms a malleable composite that can be custom moulded to almost any surface and into any shape.


Following application and over a period of several hours, the resin hardens or ‘cures’, catalysed by an organic perioxide inhibitor. This polymerization, where connections (cross-linked bonds) form between each molecule. Individually these bonds are weak, but collectively they are incredibly strong. 

Resin curing chemistry

The polymerization of unsaturated polyester resin is very well characterised. Long-chain unsaturated polyester resin molecules contain double bonds (ethylenic groups) and ester groups. Because of these double bonds they are often classified as vinyls. Curing is facilitated by cross-linking long linear chains using vinyl monomers such as styrene. Incorporating an organic peroxide catalyst prior to use. 

When blended with glass fibre mat, the composite is moldable for 10 - 60 minutes depending on ingredients and conditions. Curing renders the resin solid and very hard yet does possess a level of flexibility.

Enhanced bonding to substrates

Instances where the resin’s bond strength is likely to be too weak or merely satisfactory, a primer is used to coat the surface in advance. Primers are resin-based components with a high solvent content and added a plasticizer. It is designed to increase adhesion between the outer resin and the substrate. By forming a thin layer that penetrates into the outer layer of the substrate, it facilitates the creation of a very strong bond, virtually eliminating the chance of peeling or degradation.


Some of the most common applications focus on protecting the following:

  • Steel and GRP Water Tanks 
  • Chemical and fuel Bunds
  • Sewerage Tanks
  • Drainage Channels, gulleys and gutters
  • Floors and walls
Finished glass fibre lining, Cardiff, South Wales


As a protective barrier, it has the capacity to utilise the aforementioned attributes to provide chemical, physical, solar and in some cases thermal protection backed by decades of examples.

Outer protection

Because the lining is seamless, where a homogenous, fully adhered layer is created, any gaps, holes, cracks, etc. are filled. Here the most vulnerable aspects of your surfaces, that is, outer layers facing the greatest amount of physical and chemical stress, whether they’re concrete floors, walls, chemical bunds or internal walls of storage tanks, all are protected. Because the fibres provide a structural backbone and topcoat means that localised impact is spread across a larger area, ultimately acting as a shock absorber for the underlying surface.

Virtually maintenance-free

Furthermore, the coating requires virtually no maintenance, can withstand repeated power-washing and can expand and contract (typically 3 - 8 %) to the more extreme weather conditions, unlike more brittle resins.


In addition to the benefits listed above, the table below outlines ingredients and practices to tailor the properties of your glass fibre lining to almost any application:

Tailored strength: adjusting the ratio of resin to glass fibre mat can favour the lining to greater flexibility, or conversely greater tensile strength.

Chemical Resistance: with the potential for chemical compatibility testing, its interaction with more niche chemicals can also be evaluated.

Electrical conductor: glass fibre and its ingredients are poor conductors of electricity, so close proximity to electrical hazards is not an issue.

Drinking water compatible: standard resins can leach trace amounts of resin into water. For dry or occasionally wet surfaces, this is not a problem, but when in close proximity to water used for drinking or aquatic lifeforms, a WRAS-approved resin is a necessity.

Non-slip surfaces: applications at high risk of slips and trips necessitate a non-slip finished. Here, grit can be embedded into the external coating offering enhanced grip.

Colour choices: BS and RAL colour schemes as well as transparent coatings where appropriate.

Fire Retardant: although already low, the risk of fire can be further reduced incorporating ingredients to conform to BS476: Part 7 Class II (surface spread of flame) or Class 0 (combustibility) Class I flame spread.

Hygiene: Biological contaminants. Porous substrates like wood, concrete and corroded metals provide a breeding ground. When applied, a glass fibre lining with a topcoat finish offers a non-porous, homogeneous surface that also minimises surface-localised adhesion of biological components.

Thermal resistance: thermoset resins have a very high heat distortion point, therefore, can be suitable where liquid temperatures are higher.


Basic guidance based on best-practices for glass fibre lining installations used by Strandek is outlined below: 

1. Substrate preparation
A brief visible and physical inspection will be performed to determine the underlying qualities and the condition of the substrate material being lined will determine the most suitable preparation method. Where the underlying material still has its own inherent structure then high-pressure grit blasting is the most efficient way to prepare the surfaces of the material to be lined. This is typically used on tank walls. This will remove any existing corrosion, scale and process residues.

2. Primer application
A primer is used to enhance the adhesion between the glass fibre lining and the substrate. Due to its lower viscosity than the resin, it can penetrate microcracks and pores, whilst also offering a strong bond between the substrate and the glass fibre lining.

3. Glass fibre lining application
Resin-saturated catalysed glass fibre mat (usually 600 grams) is hand-laid on to the primed surface. A paddle roller is used to drive out air and maximise surface contact with the substrate. This layer is usually 3-5 mm thick with 5 cm overlaps are applied when wet to avoid gaps maintain consistency.

Glass fibre laminate application

4. Flowcoat finish
The final layer involves the application of flowcoat that once cured leaves a hard, impermeable, seamless outer barrier.

Topcoat application to glass fibre linings


Depending on suitability and budget costs, there are generally two instances:

Preventative measures

If your surfaces are relatively new and are expected to be exposed to harsh conditions, you might want to consider added protection as a preventative measure. Similarly, if an existing coating is performing poorly or reaching the end of its lifetime, a fresh lining system could be used.

Corrective action

Conversely, if they show signs of degradation, then we’d recommend a lining system. The benefit of this can be easily illustrated for a water tank. Over its lifetime, the walls of a water tank degrade and accumulate debris - in some cases biological contaminants. Rather than ordering a new water tank, you could re-lining it with glass fibre for a fraction of the cost. This could increase its lifetime to 10-20 years, render lined surfaces “new” and save you the purchase, delivery and installation costs of a new tank, not to mention associated downtime.

GRP lining for water feature, Cardiff, South Wales


Several alternatives to glass fibre lining systems are also available. These do demonstrate exceptional characteristics in their own right, with applications in resin flooring through to protective coatings. However, none of these offers the broad, consistent performance seen with glass fibre.

Examples include tiling, which does offer impermeable shielding but is compromised by grout lines susceptible to moisture penetration and bacterial growth. Other resin-based alternatives such as epoxy and polyurethane are exceptional in their own right, but are significantly more expensive, often presenting thinner coatings (0.5 - 1 mm versus the 3 - 4 mm of a glass fibre lining). Polyurethane, another resin can be more temperamental during application and is considerably more expensive.


The are several limitations to the use of glass fibre lining systems, that like other resins centre on the installation conditions and the technician’s level of experience. These are controllable by adhering to strict protocols, installation conditions and a rigorous quality control regime. This is why a full assessment is performed in advance to identify the suitability of a glass fibre lining system. Instances, where a different coating system is deemed superior, will also be identified.

Variability: due to fast curing times, the technicians must work efficiently to ensure a smooth, even surface. Other factors include incorrect mixing, incorrect or poor-quality chemicals and ingredient ratios and improper surface preparation.

Moisture absorption: if the glass fibres are not saturated in resin, they have the capacity to pull moisture into the composite. Over time, moisture absorption (via capillary action) into the composite can deteriorate the fibres, ultimately weakening the composite. This is why the removal of weak, damp substrate and application in a “dry” environment (Impact of humidity on the durability of E-glass/polymer composites) is preferable. This also applies to the underlying substrate, which should be dry and free from moisture. 

Operating conditions: although versatile and durable, if the working environment is outside the prescribed conditions, where incompatible chemicals are used, or substantial impacts occur, then we would expect degradation proportional to the severity.

Installation speed: instances where a seamless, durable and waterproof flooring system is required, the customer can afford limited downtime (several hours), we would recommend methyl methacrylate (MMA), a single-layer resin with exceptionally fast curing times (< 2 hours). Selected for milder environments, it is not as robust as glass fibre, but does surpass it in curing speeds.


If you’re considering glass fibre lining system for your project, whether it’s a water tank, chemical fuel bund or concrete floor, or if you would to speak to our technical team on 01633 250652 or send an email to [email protected].

Established in 1976, Strandek GRP Systems are experienced installers of high-quality linings, working across all sectors.

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Since 1976, Strandek has provided high-quality glass fibre and other resin-based coatings to a range of satisfied customers in industry, government, construction and residential sectors alike. 


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