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Club Marine

In the last issue of the magazine, we described many of the pre-winter maintenance tasks that preserve the condition of vessels as they sit languishing for expended periods over the colder months. In this article, we will describe some of the maintenance tasks that can be performed over the winter months to preserve the exterior of your vessel.

Firstly, we will look at the types and correct application of the many and varied kinds of paint and varnishes that are available. And we’ll also take a look at the vexed question of antifouling paints and investigate how to repair and preserve the exterior of fibreglass boats.

Types of Paints and Varnishes

Paints and varnishes can be categorized into four distinct types,
as follows:
1. Alkyd/oil-based paints and varnishes, often referred to as enamel paints
2. Vinyl paints
3. Two-pot polyurethane paints and varnishes
4. Two-pot epoxy paints.

Alkyd/Oil-Based Paints and Varnishes

The alkyd/oil-based paints and varnishes commonly used today were developed approximately 60 to 70 years ago. The development and application of pure oil-based paints started approximately 100 years ago. The primary constituents of these paints were linseed oil and shellac, while the main constituents of modern oil-based paints and varnishes are a special resin, solvents, and a number of agents to enhance colour, drying characteristics, stability, resistance to ultra-violet light and the usability characteristics of the paint or varnish.

The resin is brewed primarily from ingredients such as vegetable oil and glycerine and small quantities of other ingredients. The glossy finish produced by the paint or varnish after drying is a function of the resin. Typically, mineral turpentine is used as a thinning agent, although some products require special thinners due to their particular chemical make-up. There are some alkyd/oil-based paints that use water as a cleaning agent, but I wouldn’t recommend them for marine applications.

The advantages of alkyd/oil-based paints include cost of purchase, ease of application and the clean-up afterwards is simple. The disadvantage is their susceptibility to the hard knocks that all boats are subject to from time to time. However, research and development is improving the characteristics of these paints all the time.

Vinyl Paints

These are a specialized category of single-pack paints. Based on an organic vinyl resin dissolved in a solvent, they often have aluminium-based pigments added. These paints are usually used in underwater applications and offer excellent water resistance, ease of application, easy recoating and/or over-coating, due to their very tolerant nature.

Two-pot Polyurethane Paints and Varnishes

Two-pot polyurethane paints are a more recent development, a spin-off from the space and aeronautical industries. This type of painting system has been used in the marine industry since the early ’70s. Just before application, the paint must be thoroughly mixed with a hardening agent. Most two-pot paints and varnishes have been developed for coating areas above the waterline. Generally, it is not recommended that two-pot polyurethane paints be applied in areas that are permanently immersed. They also require a special thinning agent that can be expensive to purchase.

The advantage of this system is that it will produce a hard and durable finish that will retain a mirror-like glossy finish for an extended period of time – typically five to seven years, if cared for. Some of the disadvantages include high cost and the fact that they can be more difficult to apply than alkyd/oil based paints, although this is being improved all of the time.

Two-pot Epoxy Paints

  A two-pot epoxy-based paint has been sprayed onto the bottom of this new yacht to seal the gelcoat and fibreglass from moisture, prior to the application of the antifouling.

Two-pot epoxy paints are an even more recent development, although they have been available for some time now. Their primary application is surface preparation, including primers, undercoats and anti-corrosion preparations. Prone to yellowing or discolouration when exposed to light, epoxy paints are typically used underneath two-pot polyurethane paints to produce a highly durable finish.

The advantages of these paints include their superb adhesion characteristics, toughness and non-permeability to water. All these characteristics make for a finish that yields an extended serviceability. The disadvantage is the cost. Like polyurethane paints, epoxy-based paints require special thinning and cleaning agents.

Which to Use

  Well maintained varnished topsides always look fantastic and are a credit to owners’ dedication. The use of two-pot polyurethane varnishes will greatly reduce maintenance.

Certain types of construction are better suited to one type of painting system or another. Generally speaking, two-pot polyurethane and epoxy painting systems are best suited to hard surfaces, where little or no movement of the structure occurs due to temperature, humidity or structural loading. Typically, these paints are applied to vessels of composite, fibreglass, steel or aluminium construction.

Traditional construction methods, such as those used on timber carvel-planked vessels, are very sensitive to temperature, humidity and structural loads and are best protected by alkyd/oil based paints. Alkyd/oil-based paints will ‘move’ with the surface and will readily accommodate any expansion and contraction. But if polyurethane or epoxy-based paints are applied to surfaces that tend to move, they are highly likely to crack and peel in a very short time.

Application Methods

  Brush painting can produce great results if done carefully
  Varnish that is applied when the weather is too cold or humid will often result in a milky finish. The only way to fix this is to sand the bright work back heavily and re-do the job.

Paint and varnishes can be applied using brushes, rollers or by spray gun. While any application technique can be used, some may be more suited to a particular situation than others.

Alkyd/oil-based paints respond well to application by brush and/or roller, although they can also be sprayed on. This said, I have to say I have seen some outstanding finishes using a brush. It takes a little extra preparation and some practice, but the results can be well worth it. Applying paint using a roller tends to result in a thicker coat, which is not always ideal. However, using a very short hair roller or high-density foam roller and then brushing out the paint with a good quality wide brush can yield superb results. Using a brush after the roller in this manner is called ‘lining off’ or ‘tipping off ’.

Spray painting will usually yield a high quality and durable finish from the two-pot polyurethane paints. Some paints are specifically designed to be applied only using spray painting techniques, however others may be brushed on quite successfully. I would always strongly recommend speaking to the manufacturer before purchase and application.

The modern two-pot epoxy-based paints can be applied using any application technique. However, again I would strongly recommend consultation with the paint manufacturer before selecting and applying the product.

Storage of Unused Paint

Two-pot polyurethane and two-pot epoxy-based paints usually don’t store well, especially after being opened. The small amount of air trapped in the partly-used tin will cause the hardener (part B) to gel and eventually go hard. Epoxy paint hardeners (part B) rapidly discolour, which reduces their effectiveness. The paint (part A) may also deteriorate, so it is a good idea to only buy what is required for the job. As a guide, some typical storage limits are as follows:
Unopened tins of two-pot paint:
Part A – Approximately two years
Part B – One to two years, depending on the manufacturer and product
Opened tins:
Part A – Up to two years
Part B – A very short time, depending on the manufacturer and product
Alkyd/oil-based paints usually keep very well, especially if they’re quality products. The trick is to ensure the lid and rim of the tin is spotlessly clean before re-sealing.

Surface Preparation

  All of the paint has been stripped off this hull prior to repairs and repainting.

It can not be over-emphasised that good surface preparation is the key to a solid, long-lasting and high quality finish. As a general rule, the more time spent on surface preparation, the better the completed job will look and the longer it will last. Whilst sanding and filling is a laborious task, a little extra effort and patience will ensure a better finish and assist the paint to last longer, thereby optimising your investment.

Antifouling Paints

Antifouling paints can be classified into two main types:
1. Eroding paints, sometimes called soft leaching paints
2. Hard or contact paints

Both types can be further sub-divided into two categories based on the type of toxin or poison (biocide) used. The first is copper-based, in which the main biocide is copperous oxide (the natural form of copper), together with booster biocides of various types. The second category, often referred to as ‘copper free’, in fact utilises cuprous thiocyanate, a less potent form of copper. These ‘copper free’ antifouling paints can be formulated into a wide range of bright colours.

Cuprous thiocyanate-based antifouling paints are generally not as effective or long lasting as the copper-based biocides. The biocide used is always displayed on the label of the tin and in the manufacturer’s information brochures.

The use of tin as a biocide has been banned in many countries because it is a heavy metal poison that contaminates the food chain and is very hazardous to human health.

Eroding or Soft Leeching Antifouling Paints

Soft leaching antifouling paints work by allowing the surface of the paint to slowly wash away, thus exposing fresh biocide to the surface. By the end of its useful life the paint has almost completely disappeared.

Hard or Contact Antifouling Paints

Hard or contact antifouling paints work by slowly leaching the biocide through the paint film into the water. Thus, at the end of its useful life, most of the original paint film still remains on the surface.

Choosing an Antifouling Paint

The choice between a hard or soft antifouling paint depends on a number of variables, including local water temperature, pollutants in the water, the frequency of use of the vessel and type of vessel. Vessels that are fast or are frequently subject to heavy seas should not use soft antifouling paints, as the additional water friction will quickly wash away the paint. A technique that is occasionally recommended by some paint companies is to apply a hard antifouling and then apply an eroding paint on top. This provides good protection in a wide variety of applications. However, I would always strongly recommend consultation with a quality paint manufacturer before making any changes to your current antifouling scheme or when painting a new vessel for the first time.

An antifouling paint with a non-copperous oxide biocide should always be used on all aluminium vessels and their appendages. If a copper-based antifouling paint is applied to an aluminium vessel, the two metals will set up a galvanic reaction (a form of corrosion). This will cause extensive damage to any aluminium surfaces. Before antifouling an aluminium or steel vessel, or appendages such as a propeller leg, it’s always advisable to apply an epoxy- or high quality vinyl-based anti-corrosion paint to ensure a strong waterproof barrier has been established between the metal hull and antifouling paint.

All paints allow a certain amount of moisture to penetrate the paint film, however epoxy paints have a permeability rate almost too low to measure. The two-pot polyurethane paints follow closely behind, while the alkyd/oil-based paints have very poor resistance to moisture.

All good quality marine paints have been formulated to meet the specific needs of that product’s intended end use. So it is important to understand the intended use of the paint before purchasing and applying the paint or varnish. Other considerations are issues such as surface type, surface quality, expected use, expected life before recoating is required, cost and your expertise/experience in applying that type of paint.

Applying Antifouling Paints

  Good surface preparation and spray painting with a quality two-pot polyurethane paint can produce a finish that looks better than new.

This is a contentious issue with many boat owners, as most believe that rolling on antifouling paint is the best method. However, manufacturers frequently advise that spray painting is the best method, especially if an airless spray gun is used. The main issue is coverage and the evenness of application. Always calculate the underwater area of your boat and consult the manufacturer of your chosen antifouling paint to find out how much paint is required. Keep applying coats until all the paint has been used. It is also wise to pre-coat areas that are subject to lots of sunlight and additional turbulence. These areas include the entire keel, rudder, skeg and around the waterline. Sunlight promotes growth, which is why the waterline area is always the most heavily coated.

Application by spray painting will usually ensure a more even coat than with a brush or roller. The final finish will also be markedly improved, thus enhancing the performance of the vessel.

Fibreglass Boats

Fibreglass boats tend to suffer innumerable chips, cracks, scrapes and other forms of damage to the gelcoat. Even brand new boats are not exempt and can require minor repairs. Hulls, and especially deck mouldings, are susceptible to damage as they are being released from the female mould, especially if the mould is new.

If damaged areas are not repaired, it can lead to a gradual breakdown or delamination of the fibreglass in the surrounding area, thus weakening the structural integrity of the vessel. Damaged areas that are subject to frequent exposure to water or, worst still, constant immersion, are of particular concern. These areas include around the waterline, on the deck near the gunwale, in the moulded deck tread or any ridges in the moulding that can trap even a small amount of water.

Many older vessels frequently have a considerable number of chipping from many years of accumulated use and abuse. They may also show battle scars on the topsides resulting from scrapes from dinghies, wharves, pontoons, etc. Poor construction techniques can also cause problems. The first layer of fibreglass laid up against the gelcoat (the pigment layer on the outside) must be applied with considerable care to avoid any bubbles under the gelcoat. Air pockets can soon become chips or open blisters in the gelcoat. I have repaired blisters as large as a fifty-cent piece in gelcoat that were caused by careless lamination techniques.

Gelcoat Repairs

  Severe damage has been caused to the laminate of this vessel due to the inadequate size and poor installation of this fitting. The gelcoat on the deck was also badly cracked. The laminate must be fixed before the gelcoat repair is carried out.

Repairing gelcoat is not a difficult process, although it is usually time-consuming. However, it can be quite a pleasant task while sitting on the mooring or with the vessel on a trailer in a quiet area, on a sunny day with a cold drink at hand.

The first and most important job is to ensure the area in and around the damage is free of any loose material, such as flakes of gelcoat or bits of loose fibreglass. It must also be very clean and completely dry. Wipe the area with acetone to remove any grease, oil, wax, etc. When the acetone has dried, mask the area with masking tape to ensure any spill-over can be easily cleaned up.

If the vessel is more than a year old, the exposed fibreglass laminate should be wiped over with styrene to soften the surface and assist the bonding process between the new gelcoat and laminate. Styrene should make the surface slightly sticky to the touch.

After the styrene has been applied and left for a short time, the area is ready for the new gelcoat to be applied. Mix the gelcoat with the catalyst (often known as MEPK) at two per cent by volume or mass. Always read the mixing instructions on the container. Be careful to thoroughly mix the gelcoat and MEKP as it is very easy to miss some of the gelcoat, resulting in ‘dead spots’. When mixing very small quantities, as is usually the case with gelcoat repairs, it is particularly important to mix thoroughly.

Using a small brush – an artist’s brush for very small repairs – carefully paint the gelcoat into the damaged area. Keep adding gelcoat until it is a little higher than the surrounding surface.

Gelcoat blisters such as this are the result of poor lamination techniques during construction. Note the two smaller blisters
to the right.
Gelcoat chips on the edge of the deck tread are frequently the result of poor construction practices.

Leave the gelcoat to harden for at least 24 hours before attempting the next step. The repaired area should be covered with masking tape or plastic to prevent exposure to moisture overnight. When the gelcoat has thoroughly hardened, use 400-grit wet and dry with fresh water and very carefully sand the area down until it is flush with the surrounding surface.

Next, use 600-grit wet and dry (again with fresh water) to remove the scratches left by the 400 wet and dry paper. For a really professional finish, complete the process by using 1000- or 1200-grit paper. When using wet and dry paper, always use a sanding block employing a circular motion (small circles) rather than a back and forth movement. The circular motion will reduce the amount of harsh scratching and produces a better finish. Do not be tempted to use a mechanical sander, as it will quickly spoil the job. Also, electricity and water are a very dangerous mix.

After sanding, you may find that there are still some small hollow areas in the repaired section. After the gelcoat is thoroughly dry and clean, wipe the surface over with acetone, then paint in more gelcoat and once hardened, sand again to a smooth, even finish.


When all gelcoat repairs are complete, apply at least two coats of fibreglass polish. Automotive wax is not recommended as it may damage or discolour the gelcoat.

The surrounding area needs to be polished to blend in the repaired area with the rest of the surface. The area being polished should extend out to an edge or a line where the shape of the moulding changes rapidly to mask any slight colour variations. Several coats of polish should be applied for best effect and lasting protection. Most manufacturers advise that gelcoat polish should never be applied on a hot day or in direct bright sunlight as the solvents in the wax will evaporate too quickly, making it hard to work the polish up to a glossy finish.

When using a lambs wool buff on an electric polisher, it is important to always keep the polisher moving. If the polisher is held in one position for any length of time there is a risk of overheating the polish and producing a burn mark. Burn marks can usually be removed by carefully applying a very small amount of styrene with a rag and then thoroughly wiping the area with acetone. The styrene should remove the burn marks and all of the wax. Leave the area to dry thoroughly before applying several coats of polish.

Gelcoat manufacturers usually recommend that a coat of polish should be applied to a fibreglass vessel every six months, although I rarely see this happening. However, vessels that are polished every six months certainly stand out from the crowd.

Badly Damaged Gelcoat

For gelcoat that has too many blisters or cracks, the only method of repair is to prepare the surface and paint it.

Before proceeding, it is important to first establish the cause of any gelcoat cracks and investigate if the crack extends into the laminate. The laminate may need to be strengthened to prevent further damage to the structural integrity of the vessel. This may require professional advice.

All of the blisters should be thoroughly cleaned out, with any loose material removed. The crater should then be filled with an epoxy filler. Next, the entire area should be heavily sanded to ‘break’ the surface. Sanding will also ensure all gloss, wax, dirt etc. is removed from the surface. It should then be spray painted with a two-pot polyurethane or epoxy undercoat, before applying a final gloss coat. Some paint manufacturers recommend applying an etch primer before undercoating. Either way, consult a reputable paint manufacturer before proceeding.

Before attempting repairs to any underwater areas, I’d recommend seeking the advice of a professional.

Deck Tread

Deck tread that has been freshly polished should not be slippery under-foot as the moulded deck tread should provide adequate grip. If the deck tread is badly worn and no longer provides sufficient grip, the only satisfactory solution is to sand off the residual pattern and apply a non-skid surface.

Handle With Care

Following are some important guidelines to be followed when using fibreglass materials.

Styrene is very hazardous to health and should never come into contact with the skin. Gloves should be worn at all times. Styrene is a carcinogen and warrants the utmost care. Always be sure to minimise the amount of fumes inhaled and always try and wear a respirator, especially in confined spaces.

Like styrene, MEKP is very hazardous to humans. It is also a potent carcinogen. It is imperative that gloves be worn at all times when handling this stuff. Again, always avoid breathing MEKP fumes and wear a respirator, especially in confined spaces.

Acetone is a very strong solvent that dissolves all of the natural oils in the skin. Excessive exposure can lead to many forms of skin irritation. Acetone can also cause permanent skin damage, so handle it carefully.

Gelcoat should be handled with care to avoid skin contact. It is also very messy and difficult to clean up if spilt. As with many of the other materials, it’s important to avoid breathing the fumes.

Eye Protection

Should any of the agents used come into contact with the eyes, it is imperative that you immediately wash your eyes with copious amounts of fresh water for at least ten minutes. You then need to visit a doctor or a hospital for a thorough examination and further treatment. It may be helpful to take a small sample of the agent responsible with you.

These agents can cause permanent damage or blindness and any contact with or near the eyes should be taken seriously.

If you are working in an awkward position or a tight corner, eye protection is a must.


  Respirators should always be worn when sanding in places where there is a dust hazard.

If you are using any of the above agents in a confined space, always set up a fan or other means of ventilation to ensure an ample supply of fresh air. A respirator should also be worn. The vapours from these agents can overcome people remarkably quickly and may cause unconsciousness. I have seen two people overcome and both took a considerable time to recover.

Skin Contact

Frequent or prolonged skin contact can result in serious skin conditions that may last a lifetime. Even short-term exposure can cause irritation, especially for those with sensitive skin. The best prevention is to wear gloves.

Where to get ‘em

The aforementioned materials can usually be obtained from a good ship’s chandler. Otherwise a fibreglass materials supply shop will certainly have everything needed. The main thing to keep in mind is that careful preparation and good advice and products will ensure your boat looks good and continues to give good service. And if you have any doubts at all, call in the experts. Better safe than sorry.

Following is a list of terms commonly found on paint and varnish labels and information pamphlets.

Shelf Life
Shelf life is how long the paint will last before it is used. Alkyd/oil-based paints usually have an extensive shelf life, while two-pot polyurethane and two-pot epoxy paints typically have short shelf lives. Paint and varnish should always be stored out of the sun, at a moderate temperature and not anywhere damp.

Pot Life or Working Time
This is the time the paint or varnish will remain usable after it has been mixed with the hardener. Alkyd/oil-based paints have an extended working time since no hardener is required.

Application Time
Some paints require the application to be completed within a specified time.

This is the recommended volume of paint or varnish that should be applied to a given area to obtain the required build up and final film thickness.

Drying Time
The time required for the paint or varnish to harden. This is usually broken up into two categories:
1. Touch Dry Time – the time for the product to feel dry to the touch. The paint or varnish is not completely dry, but it has formed a skin or gel on the outside.
2. Total Drying Time – this is the time taken for the paint to completely cure. After this time the paint of varnish has gained most of its strength and resistance properties. I would always recommend allowing additional time to ensure the paint or varnish has cured completely.

Over Coating Window
This is the amount of time before another coat may be applied without the need for additional sanding. I would always strongly recommend referring to the label on the tin and the manufacturers’ publications for all of the above information before purchasing and applying any product.