Product Information

Coating a wooden boat using polyester resin and painting using topcoat.

Note: If you want a beautiful visible wooden surface, then the epoxy method is used and this instruction is not suitable.

Prerequisites and preliminary work

It’s important that the wood is dry and as fat-free as possible. The largest gaps (>7 mm) created in a flat-seamed boat must be filled out. In a lap-jointed one, the outer corners must be planed round and the inner corners filled using either a triangular rib or putty. All wooden surfaces must be roughened as if sawn board. It is obvious that resin will adhere best to such surfaces. This roughening should be done as early as possible, as the wood dries faster and more through a roughened surface.

The less experience with reinforced plastic work, the more important it is to pay attention to the working temperature. Easiest and clearest is working at temperatures above 18°C. Working at lower temperatures (down to 12 °C) is possible, but the quality of the end result easily falls to the inferior levels. Some kind of shelter must always be arranged outdoors, because of rain and direct sun must be eliminated.

How many layers?

It is easier to solve the issue when it is known that one layer of glass fibre with a square weight of 450 g means approximately 0.8–1.0 mm in thickness. However, it is easier to coat a boat, especially a lap-jointed one, with a mat of 300 grams, which corresponds to approximately 0.6–0.8 mm in thickness. Even if the wooden structure is completely new, it should be noted that humidity and, in particular, variations in humidity inside the boat have a fairly large impact on the changes in the wood. In other words, the reinforced plastic shell must be strong enough to be able to respond to the movements of the wood. Since coating the inner surfaces of the boat completely is somewhat impossible, it is strongly recommended that the inner surface of the boat be treated with a breathable substance so that moisture can easily evaporate.

How many kilograms of resin?

When calculating the need for material, the required amount of glass fibre mat in square metres is determined first, and then converted to kilograms using the square weight of the mat. The resin volume is the mat weight times 2.2–2.5. At least 700 grams of topcoat per square metre must be applied. This occurs when you paint two layers. The first one 400 g and the second one only 300 g per square metre, as the unevenness in lamination is largely evened out during the first layer. A minimum of 300g/m2 of topcoat should always be applied to make the curing process function correctly and properly. (Topcoat is the paint which crowns the entire fibreglassing work. It’s the most important substance in fibreglassing. The waterproof one.) In addition, styrene, curing agent, acetone, venting rollers, painting rollers, brushes, rubber gloves, buckets, etc. and moisture-resistant nails are needed.

The work itself

Initially, a thinned resin is applied. Approximately 1 litre of styrene is added to two litres of resin. Here too, approximately 1–1.5% of curing agent. This priming can be done several times if everything seems to be absorbed in and hardly any layer remains on the surface. When the priming is complete and cured, the lamination is started. The resin is mixed with 1–1.5% of curing agent, depending on the temperature. If the temperature is 20°C, 1% of curing agent is added. If only 15°C, 1.5% of curing agent is required. With this kind of dosage, the working time is approximately 40 minutes. Always apply the resin first and the mat on top. The mat is then moistened with resin also from the top side. Wetting the carpet takes about 1 minute. The venting roller is used to carefully remove all air from underneath the mat. In large boats, working almost upwards, this is an absolute prerequisite for keeping the mat in place.

In the inner and outer corners, you “tap” out the air. In corners, you can also use your finger. Laminate only one layer at a time. After 1–3 (cured) layers, if desired, the laminate can be nailed in place with a division of approximately 20–30 cm. After nailing, laminate at least one more layer of glass fibre mat. After each layer, it’s good to sand lightly with sandpaper to make it easier to laminate the next layer. If, for some reason, the work is interrupted for more than 30 hours, it is very important to sand to ensure adhering. When the desired number of layers is laminated and cured, any thorns and larger lumps are sanded away. If large holes remain on the surface, they are puttied before the topcoat painting. Large puttying areas should also be coated with glass fibre mats before painting. Topcoat is mixed with 1.5–2.3% of curing agent. 1.8% at 18°C gives only about 15 minutes of working time, so the maximum amount per mixing lot is about 1 litre. Remember about 400 g/m2 during the first layer. To avoid sanding, the second layer of topcoat should be applied within 2–6 hours. However, the first topcoat must be cured before painting the second one. When working outdoors, be careful of evening dew. This means that neither resin nor topcoat, in particular, should be spread after 6 p.m..

Underdosage or overdosage of the curing agent reduces quality.

Launch

The coated wooden boat is allowed to cure for 48 hours before launch at 18 °C. Higher temperatures will speed up curing, while colder ones will slow it down