Varnishing Your Boat

Maine Varnish applictaionMost popular GRP models from the 20th century have some decorative exterior wood such as rubbing strips, handrails, hatch covers etc.  and if well maintained these can add a real charm to your boat. However, once neglected they soon become flaky and discoloured and it is amazing how much this detracts from a boat cosmetically. The main causes of flaking varnish and discolouration to wooden trims is UV damage weakening the varnish and allowing water to penetrate into the wood. The best way to prevent this is to touch up any scratches or breaks in the varnish as soon as possible after they appear preventing water from soaking into the wood. To keep varnished wood looking its best it really needs re-doing every 1-2 years.


Perhaps the most overwhelming thing people find when varnishing is the sheer volume of different marine varnishes on the market. Varnishes naturally vary in price in accordance with their quality, however budget is not the only factor to consider when choosing a yacht varnish. The main technical properties different varnishes will advertise are the effectiveness of the products resistance to UV (the major cause of flaking) as well as the products self-levelling properties; varnishes with better levelling properties will be easier to apply evenly to a surface. These are points of quality that will naturally differ as the varnishes vary in price range, however there are secondary elements to consider.

Check the application process when considering a varnish; does it need to be sanded between each coat or can you apply two or three before having to sand it down again? It’s also worth checking the drying time and how often you can apply coats to the surface, most varnishes will strictly recommend just one coat a day but some can take two. It is therefore essential to know how many coats you will need and make sure you have the time available to do so. Varnishes also vary in colour, some are near enough clear whilst others will transfer an amber or gold glow to the wood, consider what effect you want to finish with. Finally, what wood is it going on, most varnishes are fairly universal, however, if you are using a particularly oily wood such as teak some varnishes will require you to clean the wood with the appropriate thinners and perhaps seal the wood prior to application.

View International Varnish range here

International Perfection Plus Marine Varnish
At the top of the International range is their two pack ‘Perfection Plus’, a high quality varnish with a curing additive. International recommend between 2 and 5 coats to leave a terrific gloss with the curing agent to provide the hardest, most scratch resistant shell and the longest life in the range.
The next in the range are the ‘Schooner’ varnishes; ‘Schooner Gold providing the better UV protection as well as an amber hue to the wood, and the regular ‘Schooner’ providing more of a golden colour and requiring more coats than the ‘Gold’ with both requiring sanding between each coat. Next, ‘Compass’ is the fast drying varnish in the range allowing two coats per day under the right conditions and not requiring sanding between each coat.

International Original Marine VarnishFinally, the ‘Original’ is the general purpose entry in the range; a good value, good quality varnish suitable for exterior work and requiring about three coats for a nice gloss.


Application of varnishes naturally varies between products and any special requirements will be detailed on the tin. To give the most general idea of how you might apply varnish let’s assume we are using International’s ‘Original’ varnish on wooden rubbing strips and hand rails. It is of course best, if possible, to remove wooden features from the boat to varnish in order both to improve access and also avoid dripping varnish all over the hull.

Give the wood a good clean and sand it down with around 300 grit paper, remembering to sand in the direction of the grain, and give it a good wipe down afterwards with a tack-rag as any dust will ruin the finish. Choose a good quality brush, sticky varnish is notorious for pulling hairs out of brushes, Harris ‘No-Loss’ brushes are your best bet for a smooth finish.

International recommend thinning the first coat of ‘Original’ by about 10% with their ‘No.1’ thinners, this helps the varnish to really soak into the wood and adhere well to the surface. Do this in a separate mixing jug from which you can apply the varnish. Seal up the tin once you’ve measured out what you will need for a coat to avoid any unnecessary contamination and apply the thinned varnish generously from your measuring jug using long, smooth strokes in the same direction as the grain of the wood. This needs to be left to dry for at least 24 hours before being given a good sanding with 320-400grit paper.

Once completely dry and sanded remove any dust again and you are ready to start applying unthinned coats. Again don’t apply directly from the tin but separate roughly what you will need into a suitable jug or container. When applying the unthinned varnish be careful to keep strokes smooth and brush out any drips as soon as you see them as once they are tacky it becomes very difficult to correct them. Once you are happy with the coat leave it to dry for at least 24 hours before sanding again with 320-400grit paper to provide a key for the next coat, if you don’t do this the varnish is liable to peel off in large strips, use the tack rag to remove any dust before proceeding with the next coat. Repeat this process as many times as you can, or until you are happy with the finish, International recommend three unthinned coats for ‘Original’ but if you have the time there’s no reason why you can’t go further.