Nationwide Fibre Glass

How to Fibreglass a Roof in 4 Steps

How to fibreglass a roof featured.
Installing a fibreglass roof requires a great degree of care and precision.

Fibreglass roofs are made up of several different layers, creating a strong, durable, and highly weatherproof system. To understand the role of each of these, it’s useful to at least grasp the theory of how to fibreglass a roof.

For the vast majority of people, the most sensible and cost-effective way to install a fibreglass roof is to engage an experienced specialist. This is because fibreglass roof installation is an involved process, and mistakes can lead to costly issues.

Additionally, improper installation is the most common reason for fibreglass roofs developing faults. As such, it’s always best to engage with a specialist fibreglass roofing contractor to discuss the needs of your product.

In this guide, we’ll cover the four main stages of fibreglass roof installation. You’ll gain enough of an understanding of how to fibreglass roof to allow you to make an informed decision about the needs of your building project.

It should be noted that this is the most common method for installing a wet lay fibreglass roof. By contrast, other systems like Dryseal roofs are mechanically assembled onsite

Let’s dive right in.

1. Fibreglass Roof Decking

How to fibreglass a roof: decking
Wooden decks are fixed to the building’s joists or rafters.

Fibreglass roofs are built on a timber decking structure, which is typically made out of boards of oriented strand board (OSB). These are fixed perpendicularly to the roof’s joists or rafters. As such, before laying the decking, it’s vital to ensure that the existing structures are free from damp or rot.

When installing a fibreglass roof onto an existing building, there are two methods for laying the deck. These are:

  • Overboarding, where new decking is laid on top of existing decking boards,
  • Deck replacement, here the existing deck is removed entirely, and replaced with fresh material.

Overboarding can only be performed in very specific conditions, relating to the dimensions, material and condition of the existing deck. If overboarding is performed in the wrong conditions, it can lead to serious issues, which might lead to the entire roof needing to be replaced.

As such, it’s best to consult a professional on whether or not this is an appropriate strategy.

Similarly, roof decks need to be laid with a high degree of precision. Specifically, it’s important to leave what’s known as an expansion gap at the edge of the decks, where these are installed alongside a wall.

All materials expand and contract a certain amount due to changes in the ambient temperature. Failure to include a sufficient expansion gap can lead to cracking in the surface of a fibreglass roof, which can create serious problems if untreated.

2. Edging and Trims

Fibreglass roof installation: Edging
Edging is used to achieve the optimum appearance.

Edging is then used to create a smooth and seamless effect on a fibreglass roof, as well as helping to ensure proper drainage. These are prefabricated pieces of fibreglass, which cover the edge of the roof deck.

Different shaped trims are used at different parts of the roof to aid the runoff of rainwater. Of course, this is particularly important for understanding how to fibreglass a roof which is suitable for the Irish weather.

Trims are generally fixed to the decking using galvanised nails or staples, although some require a polyurethane (PU) adhesive. PU is also used to join the trims to one another. The trims are then thoroughly sanded and cleaned with acetone before fibreglass bandages are applied to create a watertight seal against the decks.

A number of things can go wrong at this stage, which can lead to unsightly edges. In extreme cases, improperly fitted fibreglass roof trims can even lead to more serious issues. As ever, if you are not confident, it’s best to leave this to a qualified professional.

3. Creating the Fibreglass Roof Laminate

When trying to understand how to fibreglass a roof, many people are confused by the process for creating the laminate. Unsurprisingly, this is the part of the process which poses the greatest risk of creating serious problems down the line.

In theory, the process of creating a fibreglass laminate is relatively simple, but in practice a great deal of precision and attention to detail is required. To ensure proper performance and longevity To understand why, let’s look in more detail at each of the necessary steps.

Measure and Cut Mat to Size

Roofing fibreglass is most often sold in 1m rolls. A professional fitter will lay these out one by one, and cut them to fit your roof properly. Corner pieces are also applied to ensure a proper seal.

Once you have all of your fibreglass matting prepared, it’s time to start creating the laminate.

Mixing the Resin and Applying to the Deck

The matting is laminated with a special resin. This is mixed with a chemical known as a catalyst, which causes the resin to cure and harden. This is first applied to the deck. Once the matting is laid down, resin is then applied to the outer surface, in order to complete the laminate.

Modern resin technology, such as the Res-Tec range, is reinforced with fibreglass CSM to provide unbeatable resistance to cracks and damage.

While manufacturers provide recommended ratios for mixing the resin and catalyst, creating the right mixture is nonetheless tricky. The amount of catalyst will determine how quickly the resin dries, but this can also be affected by the temperature, airborne moisture, and even the time of day.

This is important to note, as insufficient resin coverage on the fibreglass laminate can lead to serious issues which compromise the performance of the roof. Here, there is really no substitute for experience with working with fibreglass.

Once the correct mixture has been created, a fibreglass roof fitter will then begin coating the roof deck with resin. Once a sufficient coat of resin has been evenly applied, they will then begin laying out the fibreglass mat itself.

Laying Out the Fibreglass Mat

While the first layer of resin is still wet, it’s time to start rolling out the cut pieces of fibreglass matting and applying the top layer of catalysed resin. Each roll of matting is laid down, and coated thoroughly with the correct quantity of resin.

As the laminate begins to turn transparent, a consolidation roller is used to ensure that the laminate sets correctly. In particular, at this point there is a risk of pinholes or resin starvation occurring, which can lead to leaks or water ingress in the roofing system.

In extreme cases, these might require the entire roof to be started from scratch.

4. Topcoating a Fibreglass Roof

How to topcoat a fibreglass roof
The final stage of fibreglass roof installation is properly applying the topcoat.

The first challenge here is beginning the topcoating process at the right time. The surface of the fibreglass laminate should be sufficiently dry that it doesn’t feel sticky, but not so dry that the topcoat cannot bond to the surface.

Typically it’s best to apply the topcoat to a fibreglass roof within 24 hours of the top layer of resin being applied. This window of opportunity is shorter in hot or sunny conditions.

It’s generally a good idea to use topcoat and resin systems which have been specifically designed to work together, such as the CureIT range.

The roofer will begin by treating the edges and corners of the roof to remove any protruding material which could cause bubbles to form in the topcoat. The topcoat is then applied with sufficient thickness to ensure a clean finish and optimal waterproofing, while avoiding the risk of cracks to the surface from excessive thickness.

How to Fibreglass a Roof

One of the main reasons for the explosion in popularity of fibreglass roofs is their reliability and longevity. The simple fact is that a properly installed fibreglass roof is the most durable and damage-resistant solution for the Irish market.

However, to select a credible roofer, it’s important that you have a basic understanding of how to fibreglass a roof. This will allow you to understand the risks associated with each stage of installation, and choose a contractor who understands how to avoid them.

Nationwide Fibreglass are the top providers of fibreglass roofing products and services on the island of Ireland. We’re also experienced and registered installers of the top fibreglass roofing systems in the world. Get in touch with us today to discuss the needs of your fibreglass roofing products.

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