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.

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GRP linings are glass-fibre reinforced plastic composites produced by saturating glass fibre mat in unsaturated polyester resin. 

Such composites can be used to protect a variety of surfaces, from concrete through to steel, wood and existing glass fibre.

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

Fibreglass GRP lining Contact a GRP lining specialist


GRP linings are lightweight and extremely strong - possessing a very high strength to weight ratio, which exceeds that of certain metals. They are not as brittle as carbon fibre and are notably cheaper. These types of liners also have greater flexibility and impact absorption capacity, making them less prone to damage. They are 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.


Work performed by GRP Lining services and specialists


GRP linings are incredibly versatile and durable. This makes them excellent coatings for a variety of surfaces, including but not limited to metals, concrete and bricks, wood, as well as glass fibre/GRP surfaces.


During preparation, the resin, a synthetic liquid-based polymer such as unsaturated polyester variety 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 vinyl ester 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. 

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.

Chopped Strand Mat

The structural backing to any GRP composite is glass fibre mat. Until recently, two-dimensional chopped strand mat is produced by chopping roving spreading sheeted forms over a moving belt. Yet more recent procedures have bypassed this step. The purpose of the glass fibre mat is to reinforce and strengthen the struture. 

chopped strand mat for a GRP lining

Enhanced bonding to substrates

Instances where the liner 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. They are 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:


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 proportion of glass fibre mat can favour the lining to greater flexibility, or conversely greater tensile strength.

Resistance to corrosion: glass and polymer-based composites lack reactive properties of steel, so they provide an excellent alternative and help to eliminate the cost of corrosion.

Chemical resistance: performance regarding the interaction of GRP linings with a range of chemicals can also be evaluated by working with suppliers and manufacturers.

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 coatings and linings 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. Flame retardant composites made from fibreglass are well known. 

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 polymers 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. But first, the installer should prepare the necessary tools to install the lining. These are generally foam rollers, paddle rollers, polyester resin, chopped strand mat, resin catalyst and for surface finishes requiring a colour, a resin dye for the topcoat. If the surface will be walked on, then grit for a non-slip finish is recommended. 

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.

5. Non-slip finish
If your surface will be walked on, an anti-slip finish is recommended. This is constructed when grit is added into the topcoat during application. It is a very useful way to prevent slips and trips, particularly in wet, slippery areas. 


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 the tank degrade and accumulate debris - in some cases biological contaminants. Rather than ordering a new water tank, you could re-line it with glass fibre for a fraction of the cost - and avoid corrosion. 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.


Several alternatives to glass fibre lining systems are also available. These do demonstrate exceptional characteristics in their own right, with applications in 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 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.

Frequently Asked Questions (FAQs) on GRP Linings

Q. How much does a GRP Lining cost?

A. This can vary, depending on the nature of the work environment, the level of preparation work required and the thickness of the GRP lining.

Q. How long will a GRP lining last?

A. GRP has proven lifetimes of many decades, the overall life will depend on the quality of the installation, the type of environment that the lining is exposed to and the level of maintenance and repair work undertaken. Standard estimates range from 10 to 50 years.

Q. Can I use a GRP lining instead of full surface or structure replacement?

A. Yes, this is one of the reasons GRP linings are so popular. They can save a substantial amount versus a full replacement, particularly on bunds, water tanks, ponds, flat roofs, cooling towers and more.

Q. Who installs GRP linings?

A. In short, anyone can install a one. However, the skill level will dictate the quality of the outcome. Strandek GRP Systems use trained specialists to install GRP linings.

Q. How difficult is it to install a GRP lining?

A. It is moderately difficult because there are a number of factors that can cause the quality of the glass fibre laminate to be badly installed. Installers should carefully follow the manufacturer’s instructions or choose a trained specialist.

Q. Are there any online guides to help show me how to install a GRP lining?

A. Yes, our YouTube channel provides an overview with instructions for various GRP lining installations.

Q. Can you use a GRP lining instead of a full surface or structure replacement

A. Yes, this is a viable option but depends on: the condition of the surface and substrate, the level of preparation required to present a surface amenable to bonding and aesthetic requirements. 


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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Training & Education

Laminating techniques using fibreglass can be complicated. The nature of the coating process requires a good understanding of the correct procedures to employ not just when it's a new surface, but when it's an existing one that's suffered from water ingress and dampness. 

Whilst this information cannot be easily presented here, we can recommend a series of training courses or degrees relevant to fibreglass methods close to your location.

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All our work comes with a full risk assessment, COSHH and method statement. Our materials are ISO9001 compliant and we provide full MSDS sheets for any chemicals. If you are undertaking this work yourself, we also recommend you undertake a similar approach and follow construction industry guidelines outlined by the UK Health & Safety Executive.

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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. 


Our team have extensive experience and we pride ourselves on reliable workmanship and competitive pricing.

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