Material:

Our preferred Resin

ISO Grade SCOTT BADER

Lay-up/ Laminating resin

Properties to be considered for boatbuilding lay-up resin are:
• Resistance to water absorption;
• Strength;
• Adhesive qualities;
• Resistance to ultra-violet radiation and weathering;
• Reaction to and from other liquids and solids, e.g. drinking water and fuel oil or wet fish.
Resin Classification and Quality:
“Marine General Purpose” resin should be used which has been previously approved by an international classification society. An Iso (Isophthalic) rather than Ortho (Orthophthalic) should be requested, better again is an Iso - NPG (Neopentyl Glycol).

Classification Societies:
Bureau Veritas, Lloyds Register of Shipping, Nippon Kaiji Kyokai, Det Norske Veritas ,American Bureau of Shipping.


Lay-up resin for boatyards in developing countries will be supplied in 200-litre drums and to achieve cure (hardening) it requires a catalyst and an accelerator and can be ordered with or without the latter pre-mixed.

Inexperienced personnel can make mistakes in calculating quantities to be used which may result in wasted resin or weak laminates.

Gelcoat resinThis is the other type of resin commonly referred to in the boatbuilding industry. When cured it forms the shiny, smooth outer surface of the hull and as such is the first layer to be applied to the female mould during the laminating sequence. The name refers to use rather than any fundamental chemical difference. It also is usually a polyester resin but is more viscous as it must not drain off vertical surfaces when applied to the polished inner face of the mould. When cured it is usually harder than laminating resin and has greater weather and chemical resistance as it forms a protective barrier between the environment and the reinforced laminate of the hull itself.
Resin Putty This material is commonly used for car body repairs and on boats is used for similar purposes. It possesses little strength as it is composed mostly of a filler powder such as chalk dust which is water absorbent and should not be used on underwater surfaces unless based on an epoxy resin. In new construction it can be used for bedding deck fittings or radiusing internal corners on joints which require bonding.

Glass Reinforcement (Mats)

Chopped strand mat (CSM)
This material is specified by weight: 300, 450, 600 and 900 g/m2 are popular weights of CSM. The boatbuilder purchase it in rolls of 30–35 kg which are about 1 m in width. Note that as total weight and width of rolls is similar, the length of mat will decrease as the weight per square metre increases. The side of the material is slightly smoother than the other which reflects the smooth side of the conveyor belt on which the mat was made. It is the rougher side which should be placed down when laminating.

Continuous roving The alternative step in the processing of filaments is their formation into strands which are loosely twisted into rovings. The normal range is 60–120 strands per roving. These rovings resemble loose glass rope which can be coiled up into reels or further processed into woven roving. The reels of roving may be used to provide short lengths of glass reinforcement to strengthen areas where access is difficult or used with a spray chopper machine as a magazine supply of glass reinforcement for spray lay up. This is an automated process combining a chopper gun which reduces the roving to short lengths and sprays it with catalysed resin onto a mould (Figure 18). This achieves the same result as a layer of CSM but faster. For a uniform rate of deposit, the operator of this expensive machine should possess similar skills to a paint sprayer. It is useful in mass production situations.
Woven roving (WR)
This is the other popular reinforcement. It is purchased in a similar form to CSM and is again specified by weight. Standard specifications are 18 oz per square yard (600 g/m2) and 24 oz (800 g/m2). As in the case of CSM, other weights are available but boat designers will normally specify a laminate which is composed of commonly available materials as it passes on a cost saving to the builder.
During manufacture, the roving is woven into a cloth such that roving in the “warp” direction (length of the cloth) is continuous for the whole length of the roll which results in a high tensile strength. WR also gives a higher glass per unit volume ratio than CSM which reduces the amount of resin needed. Approximate resin to glass ratio for CSM is 2.5:1 by weight (30% glass) and for WR is 1.25:1 (45% glass). So for a large vessel whose hull shell weight is measured in tons, inaccurate resin/glass ratios or a laminate with too much CSM and not enough WR may waste substantial amounts of materials and money.
However, it is rate to find any WR in vessels of less than 6 m and equally rare to find vessels built wholly of WR. CSM laminates are normally adequate for smaller boats while wholly WR laminates do not provide a good inter-laminar bond (adhesion of successive layers) at any size. For these reasons experience has shown that normal hull laminates are best made of alternate layers of CSM and WR with extra CSM near the outside.

Unidirectional roving
This is available in standard widths as previously described. It is characterized by continuous roving in the warp direction only with no transverse roving except a light glass thread at widely spaced intervals to prevent the cloth from falling apart when handled. It is rarely found in workboats as it is difficult to keep in shape, expensive and needed only where high strength and light weight are requirements
Glass cloth
This has a similar appearance to woven roving but on a finer scale. It is available in various widths from rolls down to 25 mm. These smaller sizes, which are known as glass tape, give an indication of its uses which are, for the narrow sizes, bonding of joints and small repairs or in full sizes for giving high strength with a smooth finish and where good draping qualities are required in areas of compound curvature. It is more expensive than WR and normal weight specifications are in the range of 110–400 g/m2
Surface tissue This is very thin and can be compared to a very fine, smooth CSM but is made from blown glass staple. It is rarely used except to support a gelcoat of above average thickness or to produce a smooth cosmetic finish on the innermost layer of a laminate. It is non-structural and unnecessary on workboats.