Yacht featured above is a Grand Banks 42 called Rowena, she is a woodie from 1968, refitted by Berthon with lots of varnish work undertaken to make her look better than new. Read her refit story here – Grand Banks 42 Refit
Is it easier to varnish bare or previously varnished wood?
Either is easy but it is important to be careful with old or poorly applied varnish. Teak has excellent properties making it perfect for the marine environment but its high oil / resin content makes it tricky to varnish successfully. Below we explain why it is better not to oil exterior teak and propose other options.
What is the best varnish type for exterior woodwork?
There are two types to consider: one-pack traditional oil/alkyd based systems and one- or two-pack polyurethane based systems. The choice depends on the wood type, what it has previously been varnished with and performance expectations, including durability, water resistance and ease of use.
Is there a trick to get a perfect finish?
As always, the key to the best looking and longest lasting varnish is mainly in the preparation. Berthon advises to spend as much time as possible preparing the surface then applying the right product using the right technique in the right conditions.
Berthon has a dedicated yacht paint facility which gives our qualified paint technicians the very best environment to apply the perfect coat each time, every time!
Waiting for a slot when you are free and the sun is shining can be stressful. Berthon’s team is on site ready get your brightwork shining so you can enjoy sea time.
Berthon have a long and successful history of varnishing the exterior and interior woodwork of some fine yachts. Over the years the tried and tested techniques and systems have been honed to provide the best possible results for our customers. Below we share some of our key learnings with you.
Without any doubt Teak is the prime timber for most aspects of boat construction. It is almost totally resistant to seawater however the high resin content does make it difficult for varnish to adhere to. Under no circumstances should exterior teak ever be oiled. This produces an excellent medium for fungal growth, which while it will not attack the wood will leave it a foul black colour in damp climates. Therefore if the teak is not to be left bare the best option is to varnish. With careful preparation most alkyd based varnishes can be used however varnishes based on Tung oil phenolic are the preferred choice for oily woods. Attention to preparation is very important. Oily wood should be degreased multiple times with acetone. Two and one pack urethanes can also be used safely with teak, however most lack the flexibility of traditional varnishes therefore they should be used only on dimentionally stable wood.
Iroko is now used as a substitute for both oak and teak. Its colour is similar to teak but the grain is much more prominent and difficult to finish to a smooth surface. It is almost as hard as oak and needs the same care as teak when varnishing.
Mahogany is easily distinguishable by its rich red colour and attractive grain. This is a wood that must be very well protected. A varnished mahogany carvel hull is incredibly attractive, but so much work is involved in maintaining it. If water is allowed to enter under the varnish a very nasty black stain occurs which is very difficult to remove. Maintenance is key!
A wooden yacht left to the UV, note the black marks left from water ingress.
Varnishes used on exterior woodwork tend to fall into two types. One pack traditional oil/alkyd based, and of these there are many variations. And one and two pack polyurethane based systems. The choice of which varnish to choose depends upon the type of wood, whether it is previously varnished, and what with, and also the performance expectation – this can include wear resistance, durability and ease of use.
Traditional one pack alkyd varnishes can contain a single or a mixture of alkyd types so it is perhaps best to consider each alkyd type separately. Tung oil phenolic based alkyd resins impart a traditional colour and smell and are fast drying due to the unique structure of the oil. Examples of available Tung Oil based varnishes are Epifanes Clear Gloss Varnish and International Schooner Gold.
Whilst urethane alkyds are also fast drying and give better chemical and abrasion resistance they suffer from lower gloss and durability. Urethane alkyds are therefore best used on interior wood in high wear areas. Examples include Epifanes Woodfinish Matte and Rubbed Effect as well as International Goldspar Satin.
Silicone alkyds demonstrate the best gloss and durability for this type of product but are slow drying and can produce softer films. Therefore they tend to be blended with other alkyd types to provide optimum properties. An example of this type of varnish is International Schooner Gold.
Polyurethane varnishes can be one or two pack. It is possible to achieve multiple coats in one day as they are faster drying and their hardness and durability are far superior to their alkyd based counterparts. However in the main they are less flexible and can suffer from cracking if the wood swells or moves. Therefore they should only be used on dimensionally stable wood. The exception to this is a moisture cured aliphatic polyurethane from Awlgrip called Awlwood which has all of the advantages of a standard polyurethane but is also just as flexible as an alkyd based varnish. It is provided with a base primer in three colours, clear/yellow/red, which conditions the wood to provide and excellent base for the gloss varnish and it can be applied in multiple coats per day without sanding between coats. It has made a good impact in the market and is receiving many good reviews. Read more about this product (plus the caveats) here – Berthon use Awlgrip Awlwood Varnish.
Awlwood Varnish being used at Berthon Boat Co.
As always the key to the best looking and longest lasting varnish is mainly in the preparation. Spending as much time as possible on the preparation and using the right techniques and materials will make maintaining your varnish over the years much easier.
When starting from bare wood always make sure that your wood is free of all dirt, wax or other contaminants. Resinous types of wood like Mahogany should be degreased with a suitable solvent; most are naphtha based. Teak and Iroko, which are oily woods, should be degreased thoroughly with acetone. Moisture content should be at a maximum of 17% and all areas of rot should be cut out and replaced.
When sanding bare wood very rough surfaces should be sanded with 60-80 grit paper and then you should gradually move up the grades of sandpaper to provide a smooth finish. It is recommended to finish with 220 grit paper. It is always recommended to thin the first coats of traditional alkyd varnishes to ensure good penetration and adhesion of the varnish system.
If you are starting from a previously varnished surface ensure that this is sound before applying more product. Check that there is no cracking or crazing. Alkyds continue to cure during their lifetime and as such embrittle and crack. It is therefore better to strip back to bare wood if you are unsure of the age of the system. If using a urethane ensure that that the pervious coating is compatible by testing with the urethane’s recommended thinner to see if the product softens. If this is the case then the urethane should not be used or the previous system should be removed. An advantage of Awlwood urethane is that it can be used over both one and two pack systems. Finishing with a final coat of gloss. The more coats applied the better the longevity of the system.
And if you would like to relax, worry free, over a bottle of your favourite tipple then consider leaving the varnishing to the professionals at Berthon!