Sikkens Cetol is a member of the wood finish group of products. Similar to varnishes, wood finishes are designed to protect and enhance the natural beauty of wood, but they tend to be more forgiving with application, require less maintenance, allow the wood to breathe, and give very high UV resistance.
Wood finish products such as Cetol are designed for above the waterline use, but normal spray, rain, and washing/cleaning are perfectly fine. Salt and brackish water spray will not hurt Cetol, either. Gloss varieties of wood finish should not be used on decks or floors that may become wet, as they will become very slick and unsafe.
Many of the wood finishes such as Sikkens Cetol (except gloss), TotalBoat Marine Wood Finish (except gloss), and Epifanes Rapid Coat have a translucent pigment and will change the color of the brightwork with each coat. In many cases, it will darken light woods, and for dark woods, it will lighten the tone, so always select the color tone that you think will work best for your application. Cetol was designed for teak and other hardwoods, but many people have used it very successfully on other firs and light woods.
Most wood finishes, such as Sikkens Cetol and TotalBoat Marine Wood Finish, will not stick to previously oiled wood, and require a teak cleaning process on bare wood before application. Though these products are known for how forgiving they are, allowing you to build quickly and easily while adding a more consistent wood color to your project, the best results always come from properly prepared wood.
Most wood finish products can be applied over varnish products that are in good condition, but Epifanes Rapid Clear and Rapid Coat are primarily the only wood finish products designed to be overcoated with a varnish product. Wood finish products such as Cetol are designed for applying annual maintenance coats easily, and do not require stripping back for recoating.