Product Information

Producing a boat from a mould

In this example, a rowing boat (approximately 4 m in length) is produced.

Mould handling: If the mould in question has just been used, several releases have been made from it so far (> 6 pcs) and it is not wet from rain etc., it’s possible to start using it with by just wiping the dust and applying a gelcoat.

However, if several months have passed since the last release or the mould has been out in the rain and sun, it has to be waxed either once or several times depending on its condition. The detachment wax is a specially produced wax. In other words, the container almost always says “mould release wax”. The styrene tolerance of other waxes is always a mystery. The wax is applied thinly... levelled... polished and the solvent vapours allowed to evaporate for a few hours... Then repeat... and so on. Important: polishing only uses wits – no force, to avoid rubbing off the wax. After the last polishing, it’s good to take a so-called overnight break to ensure that the wax is properly hardened before the gelcoat is applied.

Gelcoat application is performed twice using either a brush or a roller. Spray painting is best forgotten. Apply at least 300 g/m2 each time. As the working time is only 20–25 minutes, the maximum possible amount is approximately 3 kg per round.
In this example, the surface area of a 4-metre rowing boat is approximately 8 m2, and the 3 kg is just the right amount per round.

A curing agent is administered to the gelcoat, depending on the temperature, 1.5% to 2.3%. If the temperature is only 16 degrees Celsius (minimum), between 2.0% and 2.3% of the curing agent is required. At temperatures between 19 and 22 degrees Celsius, the dosage is approximately 1.7%.

After the first gelcoat layer has been applied, the mould is turned to such a position that the styrene gas, heavier than air, can “roll out”. If the mould cannot be tilted, a fan can be used. Strong ventilation is not recommended, but a light “cow’s breath”, which slowly drives the styrene gas out of the mould. If this is not done, curing is likely to be very incomplete at the bottom of the keel. It is possible to apply the second gelcoat layer when the first one has cured enough that when a finger is gently pressing and moved around, colour doesn’t transfer. This takes approximately 2–4 hours. The maximum interval is 24 hours.

When applying the second layer, attention must be paid to the amount of gelcoat. Again, at least 300 g/m2 must be applied. With a thinner layer, the curing process will remain incomplete. It’s good to dose slightly more curing agent for the second gelcoat than for the first one, between 0.2 and 0.5 percentage points more.

Once the second layer of gelcoat has cured for the same 2–4 hours and been finger tested, lamination can be started. The first layer is usually made using a 300 g/m2 glass-fibre mat. First, apply polyester resin on the gelcoat using a roller and then place a pre-torn/cut piece of glass fibre mat on top of it. Make sure that there is resin everywhere under the mat. The same roller is used to roll the mat onto the gelcoat and to add resin in places that are not yet wet. Let’s move on to the next piece of mat. First the resin underneath and then the rug. The “joint” of the mat pieces is made by overlapping them approximately 10 cm. The overlap is slightly cleaner when it is done with torn edges. Hard rolling can be performed immediately after each piece of mat or after several pieces. Of course, before the resin gels. Hard rolling not only removes air from the laminate but also presses out extra resin from under the carpet. At the same time, the laminate becomes considerably cleaner and smoother. The overlap point is also clearly thinned and smoothed. A hard roll is usually aluminium. Plastic rollers are also available on the market, as are “bottle-brush type” of rollers. The last type is “safe” in the lamination of the first layer of mat. The angles of the aluminium roller may break the gelcoat if pressed too hard. Especially in the inner corners, in addition to the hard roll, a brush and even a finger must be used to ensure the venting. Wear proper protective gloves.

After laminating the “first mat”, allow it to cure (3–48 hours). Before continuing lamination, lightly sand the cured laminate by hand to remove any “thorns” and other unevenness, using sandpaper (P60 – P100).

From here, lamination usually continues using a 450 g/m2 mat in the same way as the first layer. Gelcoat + “first mat” makes a total of approximately 1.5 mm. Mat layers (450 g/m2) from now will give nearly 1 mm of thickness each.