Materials and tools needed for fibreglass roofing work
Fibreglass roofing supplies intended for professional and DIY users.
Fibreglass roofing kit sizes start at 1 m2 for basic repairs, increasing to 20 m2 kits and beyond for larger roof sizes.
Each kit includes chopped strand mat (CSM), Lloyd’s approved polyester resin, MEKP catalyst (hardener), grey topcoat. Tools include rollers, brushes and mixing buckets and are tailored to individual kit sizes.
Acetone and primer are both sold separately.
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Fibreglass (GRP) Flat Roof Repair Kit
£54.00–£270.00Price range: £54.00 through £270.00
Fibreglass is an excellent flat roofing material that has established...
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This product has multiple variants. The options may be chosen on the product page
Fibreglass (GRP) Flat Roofing Kit (600g)
£150.00–£1,239.00Price range: £150.00 through £1,239.00
Fibreglass is an excellent flat roofing material that has established...
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This product has multiple variants. The options may be chosen on the product page
GRP Primer
£15.00–£272.87Price range: £15.00 through £272.87
GRP Primer for fibreglass laminating. Moisture-curing primer designed to maximise...
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This product has multiple variants. The options may be chosen on the product page
Polyester Resin
£19.90–£47.00Price range: £19.90 through £47.00
Lloyds-Approved Polyester Resin. Versatile and a key ingredient in fibreglass...
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This product has multiple variants. The options may be chosen on the product page
Fibreglass Roofing Supplies
Resin Library supplies fibreglass (GRP) roof kits and materials needed for flat roof construction and repair.
These kits, along with our step-by-step guides and articles are designed to support high-quality installations and repairs.
Fibreglass is seen as the superior material for flat roofing work. Highly durable and long-lasting, a correctly installed fibreglass roof will last 30+ years.
Key items include:
GRP roof materials for laminating and topcoating: polyester resin, topcoat, MEKP, acetone, etc.
Resins and glass fibre reinforcement are sold individually. Resins are accompanied by sufficient MEKP catalyst (hardener).
Fibreglass Roofing Kits
Pre-packed kits tailored to a range of sizes, from 1 m2 repairs through to kit sizes in excess of 10 m2 for new roof construction. Materials are specific to each kit size. For instance, a 5 m2 kit will include sufficient resin and glass fibre reinforcement to build a 5 m2 fibreglass roof.
Roofing kits have an excess of materials to provide adequate surface coverage.
MEKP catalyst (hardener) is accompanied with both polyester and topcoat resins.
Tools are accompanied in most kits and are tailored to each kit size. For instance, a 10 m2 fibreglass roofing kit will include multiple polyester rollers for laminating and topcoating, as well mixing buckets.
Resin Library’s Fibreglass Materials & Supplies
The fibreglass (GRP) roofing materials and kits displayed here are intended for both new installations, upgrades/refurbishments to existing roofs and repairs.
New flat roof installations
Refurbishment flat roofs (overlays and over decking)
Commercial: apartments, office buildings, housing estates, retail and shopping centres)
Industrial: factories, porta-cabins,
Other: caravans and motor homes.
The materials offered here are designed to enable both professional and DIY roofers to install a GRP membrane and associated GRP edge trims onto existing timber decking. Timber decking itself and the underlying insulation are not sold by Resin Library.
What is a fibreglass (GRP) flat roof?
A fibreglass (GRP) flat roof is one which has a slope of 1 – 10 degrees and is protected by a fibreglass (GRP) waterproofing membrane.
The fibreglass roof membrane is applied to a wooden substrate (typically sheeted timber) in the form of a laminate (glass fibre matting and polyester resin). This is then topped off with a resin topcoat.
The term ‘fibreglass roof’ is also known as a ‘GRP roof’ or a ‘glass fibre roof’. These different terms are used interchangeably across the industry to signify the same type of roof.
Fibreglass itself is a composite – a blend of two or more materials with complimentary benefits. These are polyester resin (the matrix phase) and glass fibre matting (reinforcement phase).
History
Flat roofs have been around for a long time in various forms, but fibreglass (GRP) roofing has been a relatively recent addition. Fibreglass, developed in the 1930s and 1940s for the marine industry, expanded into construction and in particular flat roofing.
The progressive development of the chemicals utilised in the production of these roofs has greatly improved over the last 20 years resulting in advanced specifications that ensure longevity of installations for domestic and industrial projects alike.
Where are fibreglass (GRP) flat roofs installed?
Fibreglass (GRP) roofs are installed on domestic, commercial and industrial properties. Domestic fibreglass flat roofs include those on houses, garages, sheds, extensions, conservatories and orangeries. Commercial fibreglass roofing examples include office buildings, apartments and retail centres. Industrial flat roofs include storage facilities and factories.
Of these, reinforced dual-layer fibreglass laminate is used where heavy or frequent foot traffic is expected (balconies, walkways and terraces) and if equipment is installed (e.g. air conditioning units). Note that if foot traffic is expected, then the inclusion of a non-slip finish on the flat roof surface is recommended to minimise slips, trips and falls.
How is a fibreglass (GRP) roof installed?
Firstly, wooden support joists, timber decking and insulation are installed on the roof. The process for installing the fibreglass (GRP) roof membrane involves laminating followed by topcoat application. Laminating involves adding and mixing MEXP catalyst in a controlled amount to polyester resin. The catalysed resin is then applied to glass fibre chopped strand matting (CSM) using a polyester roller. A paddle roller is then used to consolidate the laminate thereby creating a thin, uniform finish whilst also driving out excess resin and residual air. Once cured (24 hours approx.), a topcoat resin is then mixed with MEKP catalyst and applied using a polyester roller only. Once this has cured (also 24 hours approx.), the fibreglass roofing layer is complete. More details can be found with individual instructions and in our Knowledge Centre Guides.
The materials and tools needed to construct a fibreglass (GRP) flat roof are available in Resin Library’s GRP roofing kits. Individual fibreglass roofing resin and other components are sold separately if needed.
What type of fibreglass is needed for a flat roof?
In general, there are four main options for fibreglass (GRP) roofing design.
450 gram CSM (single layer)
600 gram CSM (single layer)
2 x 450 gram CSM (dual layer)
2 x 600 gram CSM (dual layer)
What items are included in fibreglass roofing kits?
Resin Library supplies fibreglass roofing materials designed to cover almost all aspects of fibreglass flat roof construction. These are:
Materials
The main ingredients in fibreglass roofing kits centre on:
Polyester resin: this is a Lloyd’s Approved unsaturated polyester resin. This is a flexible fibreglass resin designed for roofing and other protective applications. It needs to be catalysed with MEKP prior to laminating.
MEKP: this is the catalyst used for both the polyester resin and the resin topcoat. MEKP stands for ‘methyl ethyl ketone peroxide’.
Glass fibre is E-glass, which is randomly orientated glass fibre strands. 450 and 600 gram CSM is available.
Topcoat: standard grey resin topcoat/flowcoat is a polyester resin-based coating system for flat roofing. This needs to be catalysed with MEKP prior to application.
Tools (Optional)
Polyester roller (long pile refill): a wool-like roller with a handle used to soak up and apply catalysed resin to the glass fibre. Polyester rollers are also used to apply topcoat to cured laminate.
Paddle roller: metal roller with grooves and handle designed to consolidate laminate by rolling across it prior to curing. The consolidation process is designed to drive resin into the matting and remove air bubbles leading to a stronger laminate. It is not used for topcoat applications.
Paint brushes: used for small areas and minor detailing of the laminate and topcoat.
Mixing bucket: plastic bucket intended to mix and prepare workable quantities of resin-catalyst mixture.
Additional Materials (Optional)
The following materials are optional and sold separately:
GRP trims
Primer
Acetone
Timber decking: not available
Insulation: not available
Maintenance & Upkeep
Once a fibreglass flat roof has been installed, occasional maintenance and inspections are recommended. This is because flat roof leaks, when they do occur, take place gradually then suddenly – at which point it is too late to rectify the leak. These are generally done to:
Unblock gutters – particularly important during autumn and winter months when leaves can clog drainage systems and cause water to overflow into the roofing membrane
Inspect the roof after damage or work to ensure that any impact from falling materials or penetration of the membrane has not occurred
Check the membrane: if a third party has installed the roof and it is showing signs of breakdown, it would be advisable to request that the roof membrane is re-applied, particularly if it is within its assigned guarantee.
Additional Design Features
The following section outlines ways property owners can add additional features to their fibreglass roofs to provide safety and environmental benefits.
Balconies, Walkways & Terraces
Dual layers of fibreglass laminate (2 x 600 gram CSM) are heavy duty designs able to tolerate added foot traffic. This means that installers could turn the flat roof into a balcony, walkway or terrace.
Environmental
Fibreglass flat roofs can accommodate a variety of additions beneficial to the environment. Flat roofs in general have traditionally served to provide waterproofing and often to support foot traffic and equipment storage. However, limited space in urban areas and greater interest in technologies designed to offset carbon emissions has meant that further environmentally friendly options have been added.
Green ‘Sedum’ Roofs
Green roofs are usually sedum-based flat roof coverings. Sedum is an alpine plant with fresh leaves and flowers that blossom during summer months. It has excellent carbon dioxide removal, with 1.703 and 1.889 kg-CO2·m−2·yr−1 estimated per year.
Green roofs offer an aesthetic benefit, promoting a greener, more natural look to urban areas, as well as acting as a level of insulation by minimising heat loss during winter and reducing heat during summer months (inside temperature was reduced by an average of 3.4 oC in hotter climates). Green roofs also encourage biodiversity to the area.
Green roofs include sedum that are positioned on top of the flat roof. Underneath the sedum plants are drainage and filter layers designed to channel rainwater away from the roof.
There are two types of green roof design: extensive and intensive. Intensive green roofs are thicker and heavier green roofing designs. Extensive green roofs are thinner and simpler and more suited for fibreglass roofs. They are generally very durable, requiring maintenance around once per year, with watering during summer months to offset excessive heat and water loss.
The inclusion of a sedum (or any other plant) is actively encouraged on urban rooftops and more information is outlined via the BREEAM website. Guidance on green roof installation is available from a variety of sources.
Solar Panels
Solar panels are a popular addition on flat roofs. They can be positioned towards the sun on stands to generate power by converting photons from the sun into electricity.
On average, 1 kilowatt panels generate 700 – 900 kWh of electricity annually, so a standard domestic system (3.5 kW) that would be placed on a domestic flat roof would expect to generate 3,000 kWh annually. Google’s Project Sunroof can be used to estimate solar generation.
This can lead to reduced electricity bills and reduced carbon footprints according to the Energy Saving Trust website.
Solar is often used to supply power and charge electric vehicles – and at large scales it can even be used to mine bitcoin when surplus energy is generated.
Wind Turbines
Wind turbines drive much of the UK’s electricity in offshore farms, typically operated by EON’s wind farm division.
Smaller wind turbines (e.g. 1.5 kWh) are also available for domestic properties. These can be placed onto the perimeter of flat and pitched roofs to meet the energy needs of a home generating 300 kWh per month.
Planning and consideration is required with extensive wind turbine advice being available online from the Energy Saving Trust.
Q. How long does a GRP roof last?
A. If undertaken correctly to correct specification and with quality materials, a GRP roof will last 30+ plus years. It is critical to select an experienced contractor.
It may suffer some cosmetic deterioration over the latter years but should remain completely waterproof under the aforementioned circumstances.
Q. What are the contents of a small GRP repair kit?
A. Generally, smaller kits (e.g. 1 m2) will contain a selection of material and ancillary items the latter of which are generally disposable and would consist of 1 No. 3” laminating brush, mixing pot, disposable gloves, resin, catalyst and matting.
Some kits may only supply the absolute basics leaving disposables to personal sourcing.
Larger areas and those requiring greater thickness will comprise brushes, polyester rollers, multiple mixing pots, hand cleaner, acetone (brush/tool cleaner), paddle roller, resin, matting, gelcoat, flow coat, gloves.
The exact quantity and size of the kit are determined by the quantity of laminating.
Q. Can I apply fibreglass onto concrete surfaces?
A. Fibreglass adheres particularly well to clean, dry, dust-free screed/ concrete surfaces.
If there is a little residual dampness then a moisture curing primer is recommended in advance.
Q. Can you walk on a fibreglass roof?
A. Yes, under certain circumstances: (1) the underlying substrate is stable and in good condition, (2) the membrane is in good condition.
If you are expecting frequent walking (e.g. terraces, walkways, balconies) require a minimum of 2 layers of 600 gram CSM – versus a single layer of 600 gram CSM or even worse, 450 gram CSM. The UK HSE provides guidance on walking on fragile roofs.
Q. What is a roofing trim?
A. A roofing trim, installed on the edges of a flat roof, is what seals the joints and drip edges, preventing moisture and rainwater from entering the roofing structure.
Q. What types of GRP roofing trims are available?
A. The following trims are commonly used:
A170: small drip for roof edge to allow drainage into the gutter
A200: standard drip for roof edge to allow drainage into the gutter
A250: large drip for roof edge to allow drainage into the gutter
AT195: external angle fitted to outer face for step detail
AT195: internal angle fitted to inner face forming upstands
B230 small raised trim to prevent water runoff
B260 standard raised trim to prevent water runoff
B300 large raised trim to prevent water runoff
D260 fillet trim for use against abutting walls
E280 expansion joint for use on some larger roofs
F300 flat trim can be used under slates and sometimes as a gutter lining
Q. What is a warm flat roof design?
A. A warm roof design involves insulation being sandwiched between two layers of timber decking.
The aim is to create an airtight construction – free of gaps, which can lead to heat loss.
The fibreglass membrane is created directly on top of the timber decking.
Polyisocyanurate insulation (PIR) is the most common form of insulation for warm roofs. PIR has high thermal performance, requiring half the thickness of other mineral-based insulation products.
Q. What is a cold roof design?
A. A cold roof design is where the insulation – less efficient than a PIR-based warm roof – is placed between the joists/rafters or in between the ceiling joists in the case of a pitch roof.
Ventilation gaps should be added between the top of the insulation and underside of the roofing membrane to allow the air to flow across.
Building any flat roofing structure requires a good understanding of the underlying structure as well as the waterproofing membrane itself.
Fibreglass roofs are second to none in terms of waterproofing, durability and versatility.
However, successful installation requires a good degree of awareness and skill in order to prevent any issues.
Problem: the final topcoat layer is showing pinholes and exposed fibres.
Cause/Solution:
You have probably not used enough resin
For 450 gram glass fibre use around 1.1 to 1.3 kg/m2 and for 600 gram glass fibre use 1.5 to 1.7 kg/m2.
Re-apply a layer of resin provided the laminate has not been exposed to rainwater.
Check the guide instructions on how much resin to apply per square meter of matting
Problem: I used plywood and the fibreglass membrane is peeling away from it
Cause/Solution:
Plywood should be subjected to some abrasive treatment with sand paper in advance. It should then be wiped and cleaned with acetone prior to applying a resin primer.
If possible, apply a layer of primer underneath the existing fibreglass layer
The resin primer is needed to facilitate the bonding of laminate to the plywood
If using OSB3 timber decking instead of plywood, sanding and primer application are not required since the timber is highly adhesive
Resin Library offers a series of instructional guides in the form of videos. These are designed to help users follow best practices when constructing their fibreglass roof.
Note: these videos are for general information purposes only. The content here does not constitute advice. Resin Library is not liable for any outcomes. The use of information linked to this document is at the user’s own risk. The content of this document is not intended to be a substitute for professional advice. Users should not disregard in obtaining professional advice.
For prospective users aiming to build their own fibreglass flat roof, a range of product guides are available. These cover critical steps in the construction process.
