The harsh weather condition in Finland from being so cold, to being wet and dry makes the dock prone to breakage and fermentation. Painting the dock once in a year with wood oil ensures it to last for many years and this is a very easy thing to do contrary to what I thought it would be. I ended up enjoying the job under a cool bright sunshine.
This paint protects the wood from absorbing too much water if not totally and we suggest it as it is not so greasy, dries very fast and easy to clean when you mess it up in your hands or toes. The price is comparable to other brands but this one is what we picked. We bought the item from Tokmanni along the way to the summer house.
About 2 Liters of oil were used and it covered up the size of about 6 meters long and 1.5 meters wide dock. If you want to paint it thicker, then you can double the amount, say about 4 Liters.
Make sure that you clean the dock first, free of particles and other foreign sticky materials if you have not cleaned your dock regularly. Sometimes bird poops are present too especially if the surrounding area is abundant with fish. You can use wood friendly soap and a brush. Then let it dry, the best is to do the next day but depending on the weather condition, it is possible to do the painting on the same day when the wood is totally dry.