Andrew Pace
Fiberglass is a popular material for boatbuilding and repairs due to its strength and versatility. When working with fiberglass, it's important to consider the type of fabric and the arrangement of its individual glass fibers, which can vary from a woven roving to a fiberglass mat. The choice between these two options depends on the specific application and the desired weight, strength, and flexibility. In this discussion, we will explore the process of fiberglassing a roving mat in a boat, covering topics such as the benefits of each type of fabric, the techniques for applying them, and the considerations for creating a strong and durable laminate structure.
Characteristics and Values of Fiberglassing a Roving Mat in a Boat
| Characteristics | Values |
|---|---|
| Materials | Fiberglass, Epoxy, Cloth, Resin, Carbon Fibre, Polyester, Wood, Gelcoat |
| Process | Epoxy wood, lay cloth, wet cloth with epoxy, resin and mat top surface, sand, paint, repair damage, smooth rough edges, build laminate, sheath hull |
| Weight | 300 g/m², 450 g/m², lightweight carbon fibre |
| Fabric Types | Woven roving, reinforcing mats, carbon fibre mats, combi-mat, fiberglass cloth, unidirectional fabric, biaxial fabric, stitch mat, chopped-strand mat |
| Benefits | Multidirectional strength, ease of processing, versatility, strong repair, light weight, high strength, low density, low material fatigue, impact resistance |
| Considerations | Cost, weight, resin absorption, number of layers, type of cloth, weight per unit area, fibre proportion, print-through, binder breakdown |
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What You'll Learn
Epoxy vs Polyester
Epoxy and polyester resins are two types of resin commonly used for boat building and repair. Polyester resin is often referred to as "boat resin" and is the most common resin used for production fibreglass boats due to its low cost. It is also quite versatile, as it can be used in combination with fibreglass reinforcements. However, polyester resin has some drawbacks. For example, it can be brittle, and it does not bond well with wood or certain other materials like carbon fibre and Kevlar. Polyester resin is also air-inhibited, which means it will remain sticky and uncured if too thinly applied or exposed to air during curing. Its shelf life is also relatively short, at only about a year.
Epoxy resin, on the other hand, is known for its superior strength and impermeability. It is also a better choice for sealing wood and bonding with certain exotic materials. Epoxy has a much longer shelf life than polyester resin, and its fumes are less strong and not flammable. However, one significant disadvantage of epoxy is its cost, as it is much more expensive than polyester resin.
For conventional small boat construction or repair, polyester resin is usually sufficient and much more cost-effective. Epoxy is generally recommended when working with wood or exotic materials and techniques, or when improved moisture resistance is required. In such cases, vinylester, a hybrid of polyester and epoxy, may also be used.
When using epoxy, it is important to note that it will not penetrate and break down the binder in a fibreglass mat like polyester will. Therefore, if you are switching between epoxy and polyester, ensure you do not have a late blush, or you will lose the bond.
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Glass Fibre Matting vs Woven Roving Cloth
When it comes to fibreglassing a boat, there are two main types of materials that can be used: glass fibre matting and woven roving cloth. Both have their own unique characteristics and are suitable for different applications.
Glass fibre matting, also known as chopped strand mat, is made up of individual glass fibres that are irregularly arranged on top of each other. This type of matting is commonly used for smaller repairs and has a weight per unit area of 300 g/m². It is highly stable and can be used with polyester resin, as the styrene in the polyester breaks down the binder, making the mat more flexible. For larger areas or where multiple layers are required, a heavier glass fibre mat of 450 g/m² can be used for added strength.
On the other hand, woven roving cloth is constructed by interweaving strong glass fibres in different directions, resulting in a neat and organised structure. This type of fabric is typically used in the construction of large boats and is ideal for achieving multidirectional strength. Woven roving is very coarse and is often used exclusively for building large boats rather than for repairs. Single strands of roving fabric can be useful for smoothing out rough edges and repairing damage to the tips of boats.
When deciding between glass fibre matting and woven roving cloth, it's important to consider the specific requirements of the project. If thickness and strength are a priority, woven roving cloth is a better option. However, if flexibility and ease of use are more important, glass fibre matting may be the preferred choice. Additionally, glass fibre matting is more suitable for smaller repairs, while woven roving cloth is typically used for new structural components.
It's worth noting that both materials can be used together to achieve the desired outcome. For example, you can use a combination of woven roving and glass fibre matting to create a strong and durable fibreglass boat. When working with these materials, it's important to follow the recommended procedures for safety and effectiveness. This includes wetting out the wood with epoxy or resin and ensuring compatibility between the materials used, such as using epoxy with a stitch mat designed for epoxy applications.
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Using Stitch Mats
Stitch and glue is a popular method of boat construction, particularly for plywood boats. It is a simple, fast, and lightweight construction method that requires very little skill and can be used to build boats of various sizes, from very small dinghies to power and sailboats 20 to 30 feet long. The process involves stitching plywood panels together, typically with wire or zip ties, and then permanently gluing them with epoxy resin and fiberglass. This technique eliminates the need for frames or ribs and allows for easy test fits and simple fixes.
When using stitch mats, the first step is to cut the plywood panels to shape. The panels are then stitched together, forming an accurate hull shape. Drilling small holes along the edges of adjoining panels and using short lengths of copper wire as stitches is a common practice. Alternatively, plastic cable ties can be used for convenience and faster tightening. The stitches hold the panels tightly together until the epoxy resin is applied and cured. Before applying the epoxy, the surface can be "wetted out" with unthickened epoxy to improve adhesion.
After the panels are stitched and glued together, the structure is reinforced with fiberglass tape and thickened epoxy. The combination of fiberglass and epoxy results in an extremely strong joint, providing a high degree of protection, strength, and impact resistance. The type of fiberglass mat used depends on the desired characteristics. For instance, unidirectional cloths add strength along the direction of the weave, while woven and knitted cloths provide multidirectional strength. Additionally, the weight per unit area of the fiberglass mat should be considered, with 300 g/m² mats suitable for smaller repairs and 450 g/m² mats used for larger areas requiring multiple layers.
Once the fiberglassing is complete, the surface is sanded to an acceptable finish. To protect the epoxy from UV light, two to three coats of varnish or paint are typically applied. This step is crucial to ensuring the longevity of the boat. The stitch and glue method offers a simple and efficient way to construct a boat, and with proper finishing techniques, a high-quality vessel can be achieved.
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Alternating Layers of Roving and Matting
Alternating layers of woven roving and matting is a good way to build up a laminate. This method was the best practice in the early days of fibreglass boatbuilding and is still used today. The two fabrics complement each other well.
Woven roving is made of strong glass fibres, which are neatly interwoven. It is used exclusively in the construction of large boats. Roving is very coarse and bulky and quickly builds thickness in a laminate. However, it also takes a lot of resin to wet out.
Chopped-strand matting, on the other hand, is a type of fibreglass mat. It is the crudest fabric, consisting of fibres chopped into strands up to 2 inches long that are laid down in a random pattern and pressed into a spongy, felt-like material. The individual glass fibres are irregularly arranged on top of each other. It is highly stable and often used for smaller repairs.
When alternating layers of roving and matting, start with a glass fibre mat with a low weight per unit area, as this is easier to shape. You can then use roving to build thickness. The quality of the laminate will be better the higher the proportion of fibres compared to resin.
It is important to note that epoxy will not penetrate and break down the binder in the mat like polyester will. Therefore, if you are using epoxy resin, you may need to buy a stitch mat that is designed for epoxy use.
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Using Carbon Fibre Fabric
Carbon fibre fabric is a great option for boat repairs if weight is an issue. It is considerably lighter than fibreglass, with similar properties, high strength and low density. Carbon fibre constructions demonstrate low material fatigue, but they are more expensive and are therefore mainly used as a construction material in the regatta sector.
Carbon fibre fabric is made from unidirectional fibres, which means that the strength of the material is in one direction. For a strong repair in all directions, multiple layers of the fabric should be applied in different directions. This is especially important when making new structural components, as high strength can be achieved without adding unnecessary weight.
When using carbon fibre fabric, it is important to note that it is not compatible with epoxy resins. This is because epoxy compounds do not contain styrene, which is necessary to dissolve the binder in the fabric. As a result, the epoxy resin will remain on the surface, and you will not achieve the desired strength and stability.
Carbon fibre fabric is also available in a knitted form, which provides maximum directional strength and wets out fast. It is compatible with polyester, vinyl ester, and epoxy resin.
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Frequently asked questions
In a fibreglass mat, the individual glass fibres are irregularly arranged on top of each other. In woven roving, the individual fibres are neatly interwoven. Roving is coarser and made of stronger glass fibres, which are exclusively used in the construction of large boats.
One good way to build up a laminate is to alternate layers of woven roving and mat as the two fabrics complement each other well. This was a popular method in the early days of fibreglass boatbuilding and is still used today.
Fibreglass is heavier than carbon fibre. Carbon fibre fabric has high strength and low density, which gives it its lightweight quality. Carbon fibre is more expensive and is therefore the primary construction material in the regatta sector.
Multidirectional strength with easier processing and less glass is achieved by interweaving the glass fibres in different directions. These glass fabrics are extremely versatile and are usually the first choice for repairs.
