Well-kept brightwork looks great on any boat and needn’t be time consuming to maintain, providing it’s given small doses of regular attention. On the other hand, if deficiencies in the system are left to develop, decay will accelerate rapidly.
If you've got problems with teak or plywood, see: How to care for teak decks and How to Prevent Plywood Delamination: Sealing Exposed End-Grain.
1. Keep a constant eye open for developing problems
The biggest problem is that once water is starts to penetrate the system it breaks down quickly. Therefore a monthly inspection for chips, dings and cracks will pay dividends.
2. Cover it up!
The two biggest enemies for varnish are sunlight and frost. The first tends to shrink the timber as it dries out and, since many varnishes are not very flexible, can cause cracking. When water trapped in the timber freezes when the temperature falls below zero, this expands and again cracks the coating.
It’s therefore worth going to the effort of protecting varnish from the ravages of sun and frost if at all practical. A varnished tiller, for instance, can be enclosed in a custom-made sleeve, while large areas of exterior brightwork, such as the cockpit of a wooden boat, will benefit from a cover that provides shade. With a sailing boat an over-boom cover makes sense for this purpose, as this will also allow excellent ventilation. A cover is also the easiest way to give some protection against frost damage for boats that spend the winter outside – an all-over design makes sense in this context.
3. Make the most of summer days
Although traditionally the brightwork of wooden boats was varnished before they were launched in the spring, this is not the best time of year to do so, as cold nights and the possibility of showers, even on otherwise fine days can ruin a newly-applied coat.
A much better bet is to save it for a summer’s day – varnishing timber on the deck of a sailing boat on a windless sunny day is a rewarding task that can be done with the boat afloat, and you have the satisfaction of knowing you’re not missing a good sail. Varnishing at this time of year also makes the most of warm temperatures and long days.
4. Understand the pros and cons of different types of varnish
Traditional solvent-based one-pot alkyd varnishes are relatively soft and have enough flexibility to minimise cracking of the coating on timber that expands with wet in winter and contracts in dry summer weather. Normally one coat is applied per day, and each coat can be sanded with progressively finer grades of sandpaper to achieve a perfect finish when the final coat is applied.
Standard polyurethane varnishes have much better wear resistance than alkyds, but lack flexibility. They are available as both one-pot and two-pot products, the latter giving a faster cure, allowing multiple coats to be applied in a single day.
A newer, though significantly more expensive alternative is flexible polyurethane varnishes such as Coelan. This can last more than twice as long as traditional varnishes and is a two-part product that allows a number of coats to be applied each day, although a separate primer is needed for the initial coats.
5. Be meticulous in your preparation
The quality of a varnished finish directly depends on the level of preparation – the boats with the best standard of finish are likely to have had far more time spent in preparation than in applying the system.
6. Don’t delay on touching up damage
Chips and dings should have loose varnish removed with a scraper, before sanding with fine abrasive paper, and with a tack cloth. For touching up, the first coat of varnish on bare wood is best thinned with 10-20 per cent of white spirit, then two further coats applied. This is an adequate temporary measure to keep the area watertight, although a further three to four coats are needed for a long-term finish. As more coats are applied, the excess that will be standing proud on adjacent sound varnish can be sanded back, until a completely smooth and fair finish is achieved.
Preparation is similar if the entire varnish system is to be re-coated, with the addition of sanding all the varnish with a fine-grit sand paper before starting work. If existing varnish is in poor condition and needs to be stripped, chemical strippers and electric hot-air guns are both effective, although the latter will save you time.
7. Develop your technique for applying varnish
This is more difficult than applying paint as the transparent nature of varnish makes it difficult to see. However, if you put your head close to the work and sight across the surface you’ll see variations in the thickness of the newly-applied coating much more clearly.
To achieving a perfect finish, each coat of varnish should be carefully laid off in a three-stage process. Start by applying the coating working the brush along the grain, then brush it out into an even layer, working across the grain. The final stage is to ‘tip off’ the brush marks, working along the grain, with the tip of the brush only just touching the surface and with no pressure applied. Done well this will create a mirror-like finish.
8. Take the time to apply lots of coats
Up to a dozen coats are needed for traditional varnishes to give long-term protection and a great finish. The first coat on bare wood should be thinned with 30 per cent white spirit by volume, and the next two with 10-20 per cent of white spirit. This allows the varnish to penetrate the timber, providing greater protection and adhesion of subsequent layers. Sanding with progressively finer abrasive paper between coats, working up to 600 or 800 grit also helps to create a perfect finish.
Applying coatings is all part and parcel of being a boat owner. For advice try reading: How to prepare and apply antifouling or How to finish your topsides: paint, polish or vinyl wraps plus a top tip from www.boats.com: Coppercoat: A Worthy Alternative to Traditional Antifouling.