IX. Restoration of destruction / Retreat #2. On the economy of the modern world and junk (crossed out) polyester resins
IX. Restoration of destruction
We begin to repair the damage caused by previous work. A clean surface is necessary for the proper adhesion of patches, repair inserts, or new layers of laminate. We remove the polyethylene that protects the work area from dust.
According to the plan, new layers of laminate need to be applied to the body. There is only one way to ensure that the new layers adhere to the old ones: increase the roughness of the surface. Carefully "matte" the old laminate with P80...P120 abrasive. Remove dust with a vacuum cleaner and compressed air. Also, any fibreglass product has a special feature – high electrical capacity. During the sanding process, the body accumulates static charge and attracts dust from the atmosphere, which is not good, especially when painting. To avoid this, the minimum requirement is to ground the body.
All layers of fibreglass must be prepared for moulding. To do this, roll out the fibreglass over the hull with a margin and cut off the layer. Lay the prepared layers in the order of installation. There will be little time for moulding, and mistakes in this process are not welcome. The manual moulding algorithm is simple: resin is applied to the body with a brush, then a layer of fibreglass is laid by unwinding it. In one layer, the fibreglass is laid with a small overlap (5-10 cm). Use a brush or spatula to wet the corners and smooth out the fabric. The key to strength is completely saturated fibreglass without air pockets. Apply the next layer of resin and fibreglass. From denser layers (inside the laminate) to less dense ones (on the outer surface).
This project used glass fabric with a density of 450, 300 and 200 g/m2, with additional reinforcement of the keel area with strips of glass fabric. This preserved the original design of the ship's designer. Various types of fabric were used. Biaxial high-density fabrics were also used for ease of installation.
After laying the final layer, apply a heavy epoxy anti-osmotic primer "wet on wet" and leave it to polymerise. Heavy anti-osmotic primer is epoxy resin with filler. This technology provides a durable base layer for further work.
What is the outcome? A durable new hull shell made of epoxy laminate over the original polyester laminate, which is not afraid of water.
Retreat #2. On the economy of the modern world and junk polyester resins
Modern boat manufacturing, like any business, must be profitable. In order to increase margins and reduce labour costs, manufacturing technologies are changing, not always to the benefit of quality.
Small workshops with limited budgets rarely use epoxy resins. Epoxies are the prerogative of sports, quality and enthusiasts.
The use of glass fabrics is also very rare due to the high labour costs involved – manual work: layer-by-layer laying of glass fabric and impregnation with resins.
If we do not use modern methods of resin dosing by infusion (see the internet), vacuum moulding, etc., we end up with a common, cheap business model for boat building.
Gelcoat is sprayed onto the mold, which will conceal all manufacturing imperfections within its solid mass, but with a glossy appearance. Next, glass veil (a type of ultra-thin glass fabric) is laid down, or without it, junk glass mat is laid down, onto which polyester resin with chopped junk glass roving is applied using a special gun. As the thickness of the future hull increases, the layers alternate: glass mat, chopped roving. There are further differences, but they are not significant in this case. What do we get in the end?
With comparable strength, a fibreglass hull will be 3-4 times thicker than a similar glass fibre hull and, accordingly, heavier. It does not matter what fibre material we use: glass, carbon, Kevlar (aramid), basalt or mixed fabrics. Interwoven fibres forming a continuous fabric structure provide high strength and resistance to loads.
Glass mat consists of randomly arranged glass fibres bonded together, resulting in a loose structure. This material is well suited for operating conditions where high loads are not present.
A similar comparison can be made for resins. Polyester resin is significantly less expensive than epoxy resin. Polyester is less durable and sensitive to water, requiring protection with gelcoat, which often becomes impermeable during use.
Polyester resin also has a special feature: it is not a structural adhesive. Hull repairs (osmosis treatment, moulding of elements, etc.) will be carried out using epoxy resins. Epoxy resin is a resin and adhesive that is completely resistant to moisture. Let's return to the workshop to repair the boat.