An Introduction to GRP Waterproofing - Topseal Systems Ltd


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Hello and welcome to this presentation for - An introduction to GRP waterproofing.



  • Aims of the presentation
  • An overview of the market.
  • Introduction to Topseal Systems,
  • The history of GRP,
  • What is a GRP roof?
  • Suitable Applications for GRP
  • Direct lay GRP Systems
  • Environment and Health & Safety Aspects
  • Achieving Specifications


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In total the presentation will take approximately 35 minutes. The aims of this presentation are, we hope:


Increase your awareness of GRP systems as a whole if it's a system that you haven't seen before or even heard of, thereby stimulating your interest in finding out more. By doing this we will increase your knowledge which is good for the industry as a whole and increase your confidence in specifying GRP systems.


Overview of the Market

Let's now look at the current marketplace split into market sectors on the left and product types on the right. Again, it might seem obvious to us all, but I think it is worth confirming.


Domestic covers private and publicly owned homes, houses, flats, apartments, bungalows.


Commercial covers everything such as offices, warehouses, retail, leisure facilities and factories. Within these sectors we can have both new build and refurbishment repair projects. If we then look at the types of systems currently available, we have: 


Hot melt systems

Hot melt systems, whereas the name suggests copious amounts of heat are required to either melt the materials for application or bond the materials to the substrate such as Bitumen and asphalt.


Single ply sheet systems

Single ply sheet systems use a single layer of generally PVC or EPDM laid or mechanically fixed to the substrate. They require adhesive and heat though not a naked flame to create joints and overlaps relying totally on the skill of the applicator and are generally not fully bonded to the substrate.


Cold applied liquid systems

Cold applied liquid systems require no heat being delivered; details such as penetration upstands and outlets can be easily and confidently formed in situ. The membrane is fully bonded to the substrate which means water cannot penetrate meets or track underneath and is highly resistant to wind uplift.


Who are Topseal?

So, who are Topseal? Established in 1992 we are part of GNB northwest who started in the early 80s another largest manufacturer of fibreglass flat roofing systems in the UK. We manufacture all of our own trims and roofing resins to ISO 9001 standards. They aren't bought from a third party, so we know that all of the materials that we produce are consistent and of the highest quality. All top seal systems have gained BBA certification after passing the rigorous testing procedures that are carried out. All top seal roofs are installed by approved contractors.


So, as the manufacturer and distributor we don't have our own installers, but what we do have is a network of installers throughout the UK who have all attended our due day training course. Their first two jobs are then assessed, and only once the inspections have been carried out and are completed to the highest standards required, are they given the approved status. This way, we can say with confidence that all works are carried out to the standards expected from a Topseal roof.


We are members of the National Federation of roofing contractors and confederation of roofing contractors. We are also in the RIBA product selector database and NBS. And we have a dedicated login area on the Topseal website to obtain technical and specification information.


The Topseal Systems

Here we have the full range of Topseal BBA certified systems. There is a standard Topseal system, Topseal HD, Topseal Double top, Topseal Green top and Topseal Direct lay. They all come with a minimum 20-year material guarantee and you can achieve a maximum of 40 years depending on which system is used.


There are over 100 different colours available. Any colours from the BS4800 range or the RAL classic range. There are also 3 different finishes that can be achieved. The first is the standard flat finish, then by using slate granules along with the topcoat, you can have either a non-slip effect for balconies and walkways. Once you’ve applied a sprinkling of the slate granules, or if you cover the whole of the roof you can achieve another non-slip finish, which looks like a felt roof once it's completed.


To add an additional feature, you can also install a simulated led roll, if you want your roof to look like a traditional led roof with a mop stick detail, as seen on a later slide.


Topseal Accreditations

As you might expect from a major UK manufacturer all Topseal systems have been independently tested and their performance verified by the major testing houses. The British Board of Agrement is the UK’s main independent body for verifying a manufacturer's claims about their product. All Topseal systems have been tested and verified by the BBA.


In the UK the hazard that exists of fire spreading to the roof of a building from a nearby fire outside the building itself, is assessed by testing representative specimens of the roof construction to BS476 part 3. Topseal achieved an AA fire rating, which is the highest available rating.


We have also been certified to ISO 9001 standards which monitors the production and processes involved with manufacturing the system. Ensuring a consistent high-quality product is produced each and every time, and that we are focused on delivering customer satisfaction, through a reliable and standardised process.


We have also been certified to ISO 14001 standards. This is the international standard for environmental management. Topseal year after year achieve this certification, showing that we are committed to operating an effective environmental management system EMS.


In addition to this, Topseal is a truly green roofing system. The timber decking used is from fully certified FSC Forestry Stewardship Council members and the product is applied without the need for heat. So, installation is both safe and environmentally neutral.


The History of GRP

You will no doubt be aware that GRP is used extensively for producing boats and water containers. However, you may not be aware that it has been around since the 1940s. Being further developed in the 50’s and is still being improved day by day. Today's GRP is far superior to that of the 40’s and 50’s. Although, the principle is still the same. A durable lightweight, flexible, fully reinforced in waterproof material, capable of being moulded to any shape.


Here are a few of everyday items, which you may come across which demonstrates the versatility and durability of fiberglass. In the top left corner, we have a HGV. The GRP components here are for the aerofoil front and side skirts.


The wind turbine blades on the mores and deserts, out in the sea withstand wind, rain, sea water, and it just doesn’t break down. Then you have baths, shower trays and whirlpools. A lot of these are made out of GRP. Then the boating industry has to withstand the impact of the boat hitting the surface of the water and being in contact with the water all year round, and always stays in perfect condition.


Then you have the car industry. This slide in particular, is to demonstrate the versatility, and shapes that you can achieve using GRP. So, if you have an awkward detail or shape to overcome, with GRP you’ll be able to overcome this. Lastly, we have septic tanks, so no matter what goes into these, they still stay intact and fully watertight.


What is a GRP Roof?

So, what is a GRP roof and how is it constructed?


We’ll start off with the ideal substrate for a GRP roof which is an OSB3 8x2 tongue and groove board. One of the main reasons for this is that it’s fibrous board, which is made up of millions of timbre particles, glued, compressed and then baked in an oven. The resin when applied absorbs into the board and bonds to these different strands giving you a superb bond to a solid 18 milometer deck. When the boards are installed, they are installed with the writing side facing up and joints staggered which gives the roof a greater strength as well as a smoother finish, as the boards lock into each other and prevent steps and a tiling effect in the deck. There is also less waste produced from your board, because the boards have a structural joint you don’t need to land on your joists. You can use the OSB3 8x4 boards. You will have to ensure the boards land on the joists and ensure that you have adequate noggins for additional support.


Alternatively, some systems allow you to use 18 milometer p5 chipboard or plywood. You can experience various problems when using plywood. One of them being, when the system cures, it shrinks slightly. And with the plywood being built up of thin layers on wood glued together, this could cause the plywood to pull apart and delaminate from itself. Another reason being, there are so many different manufacturers of plywood in the world they can finish the board with different waxes and oils. Some of which make the board too smooth and shiny, which prevents the resin from getting an adequate bond to the board. Which will also result in delamination. This time between the laminate and the deck, so you can experience lumps and bumps all over the roof surface.


Next you have the preformed edge trims, these are also made of GRP and consist of the same material that are used in the main body of the roof. And because they are the same material, it creates a chemical bond between the two, which makes it a totally seamless joint, making it impenetrable to water.


The reinforcement mat comes in two different grades. One is 450 grams, the other is 600 grams. The 450 grams is for standard use and will take foot traffic. The 600 grams is required for areas with high foot traffic and when using direct glaze systems. The matting provides a strength to the roof, without it the resin would be very brittle. The resin is polyester resin and it is the key waterproof layer. Once you add a catalyst to the resin, you would obtain a roughly a 40-minute working time and a 40-minute curing time. After about 1 hour 30 minutes, it will be fully cured and totally watertight.


The topcoat, which is usually pre-pigmented, and also required hardener, is then applied to the roof. And you should achieve similar working curing times as with the resin.


There are various guarantees available, these vary from 10-40 years depending on the manufacturer and system installed.


When can I NOT lay a GRP roof?

There are a number of things you do have to be aware of when installing a GRP roof. The most important of these being the weather. A GRP roof cannot be installed when it is wet. Once the deck has been installed, it must be kept dry at all times, until it is at least laminated.


Once it is laminated it is fully watertight, even without the topcoat.


If it does rain before you get to topcoat the roof, this isn’t a concern. Once the rain has stopped, the roof can be dried, sanded and wiped down with acetone then top coated. If it has been left for a prolonged period of time, then a thin coat of resin will need to be applied first. Unless you are using a suitable primer, you cannot lay a GRP roof directly on to felt, asphalt or concrete.


If you are installing onto concrete, it must dry and in good condition with no cracks or crumbling. If it is in a poor condition, then it should be battened out and boarded with OSB3. If you are working in confined spaces, you must ensure that there is adequate ventilation. Once the catalyst has been added and the chemical reaction is taking place, there are styrenes admitted. There is a legal exposure limit when it comes to working with styrenes, this is 100 parts per million over an 8-hour period.


A GRP roofing system is well below half the legal limit, but it does increase when working in confined spaces. Due to the moisture in a timber framed building there can be excessive movement in it, especially at sunrise and sunset, which in turn can create a noisy roof when installed on this type of structure, so it is best avoided.


Example of a Typical GRP Warm Roof

So, here is a typical example of a warm roof build up on a GRP roof. You have your 12-millimetre ply subdeck fixed on to your joists. A vapour check barrier such as visqueen is then lay in situ. Insulation is then fixed or bonded over the top. The OSB3 tongue and groove deck is then installed with the fixing at 200 milometer centres across the board penetrating the joist, a minimum of 400 millimeters.


Before trims are installed, we need to fix battens around the parameter around the roof where we have a rage trim. This requires 1 batton and then where there is a gutter it requires 2 battens. With the second batten, step down approximately 10 millimeters.


We then have the A trims which are installed at the gutter sections to allow for water runoff. Next we have the B trims to prevent water running over the edge of the roof and direct it towards the gutter.


The D trim is the wall filler trim, which is installed at the wall abutment. This is then covered with the C trim, which is a simulated led flashing and comes prefinished.


All other trims require top coating. The deck is coated with resin at a half kilogram square meter. The reinforcement mat is then rolled over the top, and then a further 1 kilogram of resin is applied of the mat.


The area is then consolidated using a paddle roller. This is one of the most important parts of the installation. The paddle roller eliminates any air bubbles, pin holes and creates in the laminate to give you a fully watertight laminate. Once the laminate has cured the area can then be top coated.


Benefits of a GRP Roof

There are numerous benefits that you achieve with a GRP roof, which include having an extremely long-life span.


When installed correctly a GRP roof will last an excess of 50 years, which exceeds most other products on the market. Once cured it is both durable in extreme heat and cold environments. Even though it is predominately for flat roofing, it can be used for a whole host of other applications, such as balconies, ponds, pools, green roofs, pitch roofs and even vertical panels. They come with fire certification depending on the manufacturer and finished coating.


Topcoat is UV in chemical resistant. It is all cold applied so no hot works involving torches or bitumen are involved. Its fast curing, the laminate will be touch dry and ready to topcoat within 90 minutes and then topcoat will be the same.


The roof is maintenance free. BBA and non-BBA certified systems are available due to its malleable properties, you can achieve practically any shape you require or obstacle you need to overcome.It is totally seamless so there are no weak spots associated with joints or wells in other systems. It is fully reinforced, making it extremely strong. Once cured you can’t cut it with a Stanley knife. Environmentally friendly in the way that once a GRP roof has been installed it won't need replacing, therefore reducing the amount of landfill. There are over 100 colours available whereas other single ply systems, you don’t have a choice. Together with the two optional slate finishes as well as the smooth finish, the combined choices are endless. Unlike felt and rubber roofs, GRP is a fully bonded system when you use OSB3. As the resin soaks into the board, ensuring an extremely strong bond and doesn’t rely on adhesives. So, it is resistant to wind and uplift.


Suitable Applications for GRP

There are various GRP roofing systems, available for various applications, these are suitable for both cold and warm roof applications, domestic and commercial roofing, walkways, balconies and terraces, green roofs, ponds and pools, refurbishment roofs and new build roofs. So now we’ll have a look at some of these in practice.


Domestic Roofing

So with your domestic roofing, you can install a standard cold roof or a warm roof, depending on building regs, so your usual domestic application will be on garages , extensions, orangeries, porches, bay windows, and dormer roofs.


Commercial Roofing

In the commercial sector you have got factories, shops, commercial premises, hotel, apartments, schools, housing associations and other types of industrial buildings. On larger roofs you will just have to allow for expansion gaps every 100-metre squared.


Replacement Lead or Copper Roofs

There are situations when you need to replace led or copper roofs, for various reasons, such as wear and tear, vandalism or theft. This is where GRP is a perfect replacement. You can install simulated led rolls or mop stick detail to replicate the detail and once top coated you won’t be able to tell the difference.  So, it is ideal for heritage roofs, listed buildings, churches, domestic and commercial roofs, if you want to add additional detailing.


Walkways, Balconies and Terraces

GRP is also ideal for balconies and walk-ways, so on a residential or commercial property or even industrial walkways for access to air conditioning units and other types of plant.


Green Roofs

GRP is also a perfect substrate for a green roof / sedum roof, green roofs are becoming very popular at the moment for domestic and commercial high-rise towers and new build properties, both the standard roll on seeden roof and the tray system can be installed onto a GRP roof.


Architectural Water Features, Ponds and Pools

Architectural water features and other water containment applications such as ponds and swimming pools can also be easily waterproofed. Just a couple of examples here, of a swimming pool on the left and a penguin enclosure on the right. 


Case Study: Whyncrest Lab

Here is a case study to an extension to a farmhouse. A warm roof construction was used, due to the underneath being a kitchen. The roof was finished with a heavy-duty GRP system which ensures it is suitable for frequent foot traffic, and finished with an anti-slip finish, glass balustrades were added to finish off the balcony.


Example of a typical GRP Direct Lay Installation

So now we’ve covered installing a new roof. We will now talk about a refurbishment scenario. Here we have an example of a typical direct lay installation. So, we have the pre-existing substrate, which is previously mentioned, can be felt, asphalt, concrete or tissue backed installation. You then have the flexible primer. Without the primer you shouldn’t install GRP on these substrates. Once the primer has cured you can then start installing the GRP as normal with the resin. Then the reinforcement mat. The second coat of resin is immediately applied and consolidated. Once the resin has cured the topcoat can then be applied.


Direct Lay GRP Systems

Direct lay systems are a cold applied liquid membrane for the flat roofing refurbishment market. This is a perfect system to use when minimal disruption to site is required.


If you have a felt roof you need to make sure it's dry and free from loose material, and then apply a coat of the flexible primer.


Once the primer has cured, it can then be laminated as you would normally. Other substrates that you can directly lay onto are concrete, asphalt, GRP, felt, insulation and some systems allow you to bond to PVC single-ply and metal cladding. The specification will differ per manufacturer and system being installed.


Refurbishment Roofs

Direct lay systems are ideal for social housing contracts, commercial jobs, churches, schools and other local authority flat roofs, and the domestic market as well.


Case Study: St Andrew's Church

Topseal were approached for specification advice for replacement of the roof on St. Andrews Church hall in St. Helens. As the building was in constant use the works needed to be completed with minimal disruption to the space underneath. Direct lay systems were selected as it could easily incorporate a number of tricky box gutters and parapet walls and be applied directly to roofs with both asphalt and bitumen substrate. The project was completed ahead of schedule. And the church hall was used continuously during the works.


New Build Roofs

It can also be used in new build situations as well as the refurb market, extensions, high rise tower blocks, commercial and domestic roofs as shown here with the canopies and roof with reluxe window details.


Health and Safety and Environmental Aspects

The environmental health and safety aspects of a GRP system are; it is all cold applied, so no hot works are involved, which are associated with felt and asphalt roofs. Which in turn makes it safe and easy to install. As expected it is the installers responsibility to ensure safe working practice. A GRP roof also has a low life cycle cost and makes it sustainable when compared to other single ply systems. Which are more expensive, and who’s life expectancy isn’t as long. Because of the extended life expectancy of the systems, any impact on the environment is minimal. Once the system is cured, it becomes inert and you won’t experience any toxic run off.


All materials in their liquid form are flammable but once cured, they are fire rated and do achieve various ratings of fire certification, which goes up to FAA fire rating, which is the highest fire rating achievable for roofing products.


With the direct lay systems as you are leaving the existing deck in situ and not removing it you are eliminating the use of skips and therefore not producing landfill.



Here is a short clip of a tile drop test. This demonstrates how hardwearing a GRP roof is in comparison with a felt or EPDM roof. You will see that when the tile is dropped it pierces both the felt and the EPDM, but just scratched the topcoat of the GRP roof, and doesn’t actually penetrate the waterproof membrane.


Achieving Specification

There are a number of things to consider when specifying a roofing system, not just a GRP system, for any sized project. You may want to take into consideration the following points when specifying a roofing system.


The training that the manufacturer of the roofing system offers and also you may like to consider using an installer that is manufacture approved through a training programme, this can eliminate issues that may happen with installations further down the line.


You may want to look at only specifying systems that have product and system certifications such as BBA certification, such certifications ensure you and your customer that the product is fit for purpose. With so many flat roofing and waterproofing systems available on the market you may find it key to consider the guarantees that your customer will receive with their installation.


Some systems will provide you with material guarantees, workmanship guarantees, and extended or insurance backed guarantees. Depending on the project you are working on, environmental standards such as ISO 14001 may need to be taken into account.


Again, depending on the project, you may need to achieve a certain fire rating, this will not only differ per roofing substrate but also per system manufacturer. Part L Building Regulations compliance as of April 2006, you may want to consider the manufacturer quality standards, such as ISO 90001 as this ensures all processes carried out are identical, ensuring a consistent quality product is produced and a customer satisfaction is practiced through an official process.


Some specifiers like to look at trade Association memberships, that the installers and possibly the manufacturers hold. Ones to consider looking at for roofing are the National Federation of roofing contractors and, Confederation of roofing contractors amongst many others. Technical and specification support should be available from leading manufacturers and this can be a big assistance to you, ensuring a smoother design and specification process through to completion.



So, a recap of the items we have covered today; various fiberglass roofing and waterproofing systems, it's all cold applied so no hot works making it safe to use, it’s fast curing, totally seamless with no seams joints or welds meaning there are no weak spots for water to gain access, it's fully reinforced with reinforcement mats which allows for flexibility in the roof when it expands and contracts.


Even though we do recommend a minimum of 180 fall, you can install a GRP roof with a 0 fall. In cases where you are restricted by a soffit or other obstacle. You may experience standing water on a 0-fall roof, but the GRP will contain the water, and it won't be broken down or fail due to this.


Simulated lead roles for detailed work are available as well as simulated lead flashings. You can obtain guarantees of up to 40 years, environmentally friendly, it's UV and chemical resistant, you can achieve various finishes by using slate granules. As well as having an extensive range of over 100 colours to choose from, it's versatile, so as well as being used for a flat roof it can also be used on a pitched roof and even vertical panels.


There are direct lay options available for jobs where removing the existing substrate is not an option and the fact that GRP can be used on jobs from the size of a canopy over a front door, right through to large industrial roofs is just another benefit of this sort of system.


I hope this presentation has been of interest should you require any additional information you can contact Topseal on 08000 831094 or


Alternatively, you can go to our websites or

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