This is a superficial overview of general procedures to install a fibreglass roof and should be used in conjunction with other articles associated with the subject or discussed with your supplier. Whilst Strandek offers a range of fibreglass flat roofing expertise ourselves – something we’ve been doing since 1976 – we also believe in promoting excellence within the industry – from other flat roofing specialists to DIY enthusiasts.
What is Fibreglass?
Fibreglass is a composite material, one which consists of a resin and reinforcement chosen according to desired mechanical properties and the application.
In the case of fibreglass (GRP) composites, both unsaturated polyester resin and glass fibre chopped strand matting (CSM) are combined.
Unsaturated polyester resin (whereby polyester resin is used for short) is combined either in the form of pure resin or in the compounded form with fillers find a wide range of applications. Glass fibres are the most popular form of reinforcement, accounting for 95% of the consumption of fibres for plastics reinforcement.
The main applications of fibreglass are in the construction industry (non-reinforced or glass fibre reinforced products), automotive industry, yacht construction and in this case fibreglass roofing.
Why is Fibreglass an Excellent Flat Roofing Material?
Fibreglass is an incredibly effective flat roofing system with many applications. It has been used extensively in the construction industry, accounting for a large proportion of the GRP fibreglass composites market.
As a composite, it offers exceptional properties strength, durability, broad chemical resistance, waterproofing, abrasion, and moderate impact resistance as well as a range of other features. It is also very cost-effective as a flat roofing system.
Fibreglass Roofing Installation Guide
The following section is a basic outline and guide for prospective installers of fibreglass roofs. Resin Library, a supplier of fibreglass roofing kits offers a 5-part series on how to install a fibreglass roof.
Note: fibreglass flat roofing – as with any other roofing work – carries risks. Installers intending to undertake such work should refer to the UK HSE website for more detail on how to safely manage roofing risks involved.
Fibreglass (GRP) Roofing Kits
This guide assumes the installer is intending to install their own fibreglass (GRP) roof. In order to do so, it would be wise to source a fibreglass roofing kit. These come in a range of sizes tailored to the surface area of your flat roof.
Materials typically include polyester laminating resin, glass fibre matting, MEKP catalyst, topcoat, as well as mixing containers, paddle rollers and polyester rollers. GRP edge trims are also used to surround the perimeter of the fibreglass flat roof.
The quantity of materials needed depends on the roof size.
Step-By-Step Guide: Installing a Fibreglass Roof
To provide a fibreglass GRP roof covering to a flat roof there are certain foundation elements that should be in place before you start. The following instructions outline how to build a fibreglass flat roof. This is important to prevent water ingress and ultimately a reliable flat roofing solution
1. A sound surface with which to apply the laminate is essential. If the existing boards (sub decking) are in good condition and the joists are sound you can overdeck the entire roof using 18 mm OSB3 8×2 Interlocking boards with adequate fixings.
Note: If, following inspection, it is found that the underlying roof surface boards have sustained substantial water damage and have delaminated or become soft they will need to be removed and replaced completely.
2. Whichever procedure is appropriate following secure fixing the next stage is to fit the preformed GRP trims to the perimeters and upstand detail to wall abutments.
Note: for grp fibreglass roofing a wide range of pre-moulded trims are available for flat roofs in up to 3M lengths to accommodate the required detail.
Note: Your roofing contractor/supplier will advise on the correct trims to use.
3. Use a 600gm/ sq.m glass fibre matting and cutting the lengths to size before you start saves time and encourages an organised work format. After mixing of resin and catalyst to suitable quantities for the intended immediate surface cover target, apply the catalysed resin with a polyester roller to the surface board and then overlay with the pre-cut mat followed by additional resin.
Note: aim for a 1 – 4 % concentration of MEKP catalyst to be added to polyester resin. This would equate to 10 – 40 mL of MEKP per kilogram of polyester resin. It is important to get this right to create a high-quality grp flat roof. Generally, 1 – 2 % is recommended in most cases as it will allow the resin to cure in a workable timeframe. elevated concentrations lead to faster curing times.
Note: a second layer of laminate can now be laid adjacent or parallel to the first-panel width. Normally, following this second application you will be able to return to this first panel and consolidate with a paddle roller. This helps provide a high-quality laminate.
Note: Depending on the size of the roof it often helps if 2 operatives engage and share in the work. Eg., flat roofer 1 mixing resin, paddle rolling and flat roofer 2 laying mat and resin application.
Continue the process described above until all areas are completed. Allow extra time and smaller resin mixes for detailing, eg vent pipes, corners etc.
4. Once complete allow curing to a stage where it is at least comfortable to walk on it without footwear adhesion. Timescale on this will depend on catalyst proportions and ambient working temperatures. Generally, it is 2 hours for a partial cure and 24 hours for a full cure. If the laminate is sufficiently dry, you can proceed to the topcoat application step.
5. Once cured, take time to inspect the laminate surface for defects which can include resin starvation, pinholes and matting burrs. All these are easily correctable and covered in detail in other advisories.
6. The next process is the final application of the flow coat layer which adds aesthetic qualities and UV protection to the roof laminate.
Note: again, following guidance notes on quantities and catalyst mixing levels apply the flow coat (generally 0.5 kg/ sq.m) to the laminated surfaces with a lambswool roller and use a brush for edge trim coating and awkward detailing.
At this stage, your new GRP roof is effectively complete if guidance advice has been followed and will provide an exceptional number of trouble-free years of protection.
A FEW TIPS!
- Don’t rush it. It will become expensive!
- Have all necessary required tools at hand including PPE…glasses, gloves, overalls and masks when appropriate. Have an eyewash at hand.
- Keep a bucket of water at hand with a resin-removing soap for hand cleaning.
- Do not use acetone for this ….risk of skin infection and irritation at least.
- Provide a dedicated material storage area with a protective baseboard for spillage.
- Pre-cut all matting and carefully roll in a sequence of requirement and keep dry.
- Observe FORECAST weather conditions and delay if not suitable.
- Too cold or too hot is not good. See advisories on line speak to a technical advisor.
- Avoid wet conditions throughout the installation. Again, it will prove expensive.
- Speak to your supplier if in doubt of a procedure or complication. Use FaceTime! It’s what it’s for!
- Keep a container of acetone at hand to clean tools if there’s a delay in procedure but be mindful of flammability!
- Expect to use a few lambswool rollers during the process so ensure you have enough.
- Generally, allow approximately 10% over the quantity of material required. This allows for wastage and mistakes.
- Consider which day you will install. If on a Saturday, be sure of adequate materials and advice. You probably won’t be able to resolve a problem post midday on a Saturday until the Monday morning!
- Use a new roller for the flowcoat application always.
- Do not smoke or consume food near the installation. Generally follow good common sense guidelines throughout.
- Have a clear plan of action for the application. Consider writing down reminder bullet points on a large sheet nearby including special advisories with the phone number of your supplier or technical advisor.
- Do talk to your supplier about the project BEFORE ordering materials and if they are knowledgeable about Glassfibre Roofing they can assist.
- Remember that residual catalysed resin or flowcoat left in a bucket can self ignite so if leaving the location for any time pour water over the surface.
- Beware catalyst spills and mopping with a cloth, paper or rag. This can self ignite.
- Never ever dispose of any of the chemicals into a drain or burn. It is environmentally illegal and if traced you could be prosecuted.
Frequently Asked Questions (FAQs)
Q. How many layers of fibreglass do I require for a flat roof?
A. Generally, one layer of 600gm/sq.m chopped strand mat is the accepted norm. You can add two layers of 450 or 600 gm/sqm as an alternative for a thicker membrane if heavy or frequent foot traffic is expected (for instance on walkways, balconies and terraces). We do not recommend a lesser specification than 600gm/ sq.m as an isolated layer.
Q. Will fibreglass set (harden) in cold weather?
A. Yes it can…even down to freezing but only with the careful addition of chemicals usually outside the remit or understanding of DIY applications. For roofing applications by DIY installers, we recommend working at no less than 15 Degrees C with correct catalyst additions. If there is a need to undertake below this temperature speak with a technical advisor beforehand.
Note: an advisory here is to consider in winter months areas that are likely to become subject to shade later in the installation resulting in lower temperatures. Consider laminating those areas first. Secondly, consider flow coating in the warmest part of a cool day. It is not uncommon for the cure of flow coat to stall if applied mid-afternoon in such conditions and remain tacky for several days. Consider flow coating at a later suitable opportunity.
Q. How much MEKP catalyst can I mix with resin?
A. Anything between 1 and 4 w/v % (volume of catalyst per weight of resin) and is determined by ambient temperature, surface temperature and required working pot times.
So, if you are preparing 10 kg of polyester resin, then somewhere between 100 mL and 400 mL should be mixed into the resin.
Note: typically, lower concentrations of catalyst are used for hotter conditions where curing is faster and higher concentrations are used for colder conditions. It is strongly advisable that you practice in advance using a small area to ensure a consistent, high-quality laminate.
Q. How do I calculate the amount of resin required?
A. One square metre of 600gm chopped strand matting (CSM) weighs 600 gms. The ratio of resin-to-mat by weight for a glass fibre roof laminate is not critical but should be in the order of 2.5 : 1. Note that the type of chopped strand matting used is E-glass .
So, 2.5 x 0.6 = 1.5 kg. So, 10 sq.m will require 15 -18 kg resin
More detail can be found about fibreglass (GRP) linings .
Q. Can you walk on a GRP flat roof?
A. Yes, unlike rubber roofs, GRP roofs are designed to be walked upon but with a few caveats. The sub-deck must be in sound condition and well secured. Laminate quality must be to a high standard. Consider an integral non-slip inclusion to the flow coat application. For roofs that are expecting frequent foot traffic (balconies, walkways and terraces), consider a dual 600 gm/sqm layer of laminate. A fibreglass roof should not be walked on if it is classed as a pitched roof without adequate controls in place.
Note: It is perfectly acceptable to overlay the installation with masonry slabs, tiles, sedum green roofing and timber decking.
Q. Can you overlay a concrete roof with GRP?
A. Providing the surfaces are dry, dust-free, reasonably smooth then GRP is an ideal waterproofing membrane for concrete. Generally, the surfaces should be primed with G4 or Primax (similar) beforehand. A video of GRP lining of concrete is available on our YouTube channel.
Note: be prepared to use more resin with some surfaces. If applying an adhesive overlay for tiles etc omit the flow coat which contains a wax solution for a secondary layer of resin generously applied to the main laminate.
Q. Where else is fibreglass used?
A. Fibreglass (GRP) is used across a range of industries, from aerospace to space and motorsports. It’s also used extensively by the marine industry. It is also used in other industries and is the subject of innovation to improve its compression properties as well as performance study.
Q. Where can I learn more about fibreglass flat roofing?
A. A range of composites courses is available relevant to fibreglassing techniques. There are also roofing apprenticeships available. There are also grants for women working in construction available. There is also a range of composite experts available in both academia and industry.
Q. What type of insulation do I need for a fibreglass flat roof?
A. A fibreglass flat roof should have the same roofing insulation (located above or between the roof joist) as any other flat roof. The existing roof may have a type that is non-compliant and so an upgrade to a compliant insulation type may be required. More detail is available from Kingspan.
Q. How does a grp flat roof compare to felt and rubber roofs?
A. A fiberglass roof has exceptional mechanical properties that make it the most durable of all flat roofing systems. A felt roof typically has a shorter lifetime (15 years) and single-ply roofs (EPDM, PVC, etc.) tend to sag and can puncture or tear easily. The strength of the glass mat combined with polyester resin creates a composite – fibreglass GRP laminate – that is the best-in-class roofing system.