What is GRP Lining?


Have you ever wondered why construction professionals always recommend waterproofing your home or water tanks before moving to a new location? Just as a house must have the right layout, it is also necessary to hire the right waterproofing company for it. Hiring the best waterproofing contractors will not only protect your home and water tanks from water ingress from the outside, but can otherwise control damage to your home’s foundation and get everything else done sooner. Waterproofing your home and water tanks is important for your family’s safety as it minimizes moisture levels and reduces breathing problems that could occur due to mold or leaks. The choice of waterproofing solutions will therefore protect everything stored inside from damage. This is especially important if you live in an environment where heavy rains occur frequently throughout the year.

Now, what’s the best way of waterproofing? Well, GRP lining is the best technique available in the market. And by saying that, Stalwart FM – one of the best facility management company in Muscat can be right choice of waterproofing contractors for your water tanks.

So, what’s GRP? GRP Fiberglass Linings and Coatings are fiberglass reinforced plastic composites produced by impregnating a fiberglass mat in an unsaturated polyester resin. Such composites can be used to protect a variety of surfaces, from concrete to steel, wood and existing fiberglass (GRP). Fiberglass repair kits are also used to repair and renovate damaged surfaces.


While talking about water tanks, whether it may be underground, overhead, sumps, etc., it’s important to waterproof them with the best possible technique. On that note, GRP lined water tanks has the best ability to prevent leaks for a lifetime. As a protective barrier, it has the ability to use the above attributes to provide chemical, physical, solar and in some cases thermal protection supported by decades of examples. Also, as compared to other techniques, GRP lining price will be a little higher.

GRP lining for underground concrete water tanks or chemical storage tanks and steel tanks prevents leakage and absorption of water and protects water from algae and mold growth. GRP Lining is a process of applying a permanent layer and lasts a lifetime. GRP lined tanks are suitable for potable water storage as we use the same materials used to manufacture water tanks.

Fiberglass coated or laminated or waterproof tanks will last the life of most equipment without leaks or corrosion failures. GRP lined water tanks are not susceptible to corrosion, they are maintenance-free. There is no need for regular testing, record keeping or replacement of protective systems. You save the difference in time, money and worry about the life of the tank and avoid possible financial obligations. Similarly, the GRP-GRP / laminated / watertight underground storage tank system can be used to store gasoline, gasohol aviation fuel (90% gasoline and 10% ethanol blend), jet fuel, diesel, potable water or waste water at ambient underground temperature, or fuel oil at temperatures not exceeding 150°F.

Properly installed, GRP-Glass Lined / Laminated / Watertight Underground Storage Tanks are strong enough to withstand constant and continuous contact with any media. Fiberglass lined underground tanks have been designed to meet specific performance criteria in dry or fully flooded holes when properly installed. GRP – Fiberglass Laminated Watertight storage tanks offer unmatched performance benefits combined with quick and easy installation.


In addition to the above benefits, given below are some other features of GRP lining.

Tailored strength: adjusting the ratio of resin to fiberglass mat can favor the liner for more flexibility or, conversely, greater tensile strength

Chemical resistance: performance regarding the interaction of GRP cladding with a range of chemicals can also be assessed in collaboration with suppliers and manufacturers.

Electrical Conductor: Fiberglass and its resinous components are poor conductors of electricity, so proximity to electrical hazards is not a problem.

Compatible with potable water: Standard resins may leach trace amounts of resin into water. On dry or occasionally wet surfaces this is not a problem, but in close proximity to drinking water or aquatic animals, a WRAS approved resin is a must.

Color variants: BS and RAL color schemes and possibly also transparent coatings.

Flame Retardant: although already low, the risk of fire can be further reduced by incorporating additives to comply with BS476: Part 7 Class II (surface spread of flame) or Class 0 (flammability) Class I flame spread. Flame retardant composites made from glass fibers are well known.

Hygiene: Biological contaminants. Porous substrates such as wood, concrete and corroded metals provide a breeding ground. When applied, the coated fiberglass liner offers a non-porous, homogeneous topcoat that also minimizes surface-localized adhesion of biological components.

Heat resistance: thermoset resins have a very high heat distortion point, so they may be suitable where liquid temperatures are higher.


Below are basic guidelines based on best practices for GRP lining. But first, the installer should prepare the necessary tools to install the panelling. These typically include foam rollers, paddle rollers, polyester resin, chopped strand mat, resin catalyst, and for finishes requiring color, a resin top coat dye. If the surface is to be walked on, then grit for anti-slip treatment is recommended. The method below refers to the “hand lay” method, a reliable and versatile form of lamination, although “spray lay methods” are also available. Standard procedures include:

1. Preparation of the background

A brief visual and physical inspection is carried out to determine the basic properties and condition of the substrate material to be lined, determine the most suitable preparation method. Where the underlying material still has its own internal structure, high pressure blasting is the most effective way of preparing the surfaces of the material to be lined. This is usually used on tank walls. This will remove any existing corrosion, scale and process residue.

2. Primer application

A primer is used to increase the adhesion between the fiberglass cladding and the substrate. With its lower viscosity than resin, it can penetrate micro-cracks and pores while offering a strong bond between the substrate and the fiberglass liner.

3. Application of fiberglass cladding

A resin saturated catalyzed fiberglass mat (usually 600 grams, although 450 grams or 4 x 450 grams of CSM) is laid by hand over the primed surface. A vane roller is used to displace air and maximize surface contact with the substrate. This layer is usually 3-5mm thick with 5cm overlaps applied wet to prevent gaps to maintain consistency.
The fiberglass mat should be cut to size for each part of the surface. This should be done before preparing the polyester resin, which should have a catalyst content of 1-3% depending on the type and amount required. This should be mixed well, but also carefully mixed to avoid excess air. It should also be used immediately, so small amounts of resin should be applied to manageable areas.

4. Surface treatment with liquid varnish

The final coat involves the application of a liquid varnish which, when cured, leaves a hard, impermeable, seamless outer barrier. Here again, the resin should be prepared in advance and used immediately as soon as it is catalyzed and mixed.

If you are considering fiberglass lining (GRP lining) for your underground or overhead water tanks or sumps waterproofing, then contact our technical team of Stalwart FM, we are ready to help you.

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