Surface prep is really easy for Sikkens Cetol Marine because sealers or thinning are not necessary, nor are they advised.
For bare wood, remove any surface contaminants, dust, grease, wax, or oils. If the wood has contaminants in the grain or has aged to a gray tone, do not attempt to sand them away. Instead, use a quality teak cleaner, as directed, to remove discoloration and stains. Allow the wood to dry, then use 180-220 grit sandpaper to sand the wood, in the direction of the grain, until smooth.
Wood that was previously coated with anything but a Cetol Marine wood finish product must be stripped back to bare wood and prepared as such.
Before applying Cetol, ensure that the moisture content of the wood is below 18%. Do not thin or seal the wood with any products. Apply Cetol Marine liberally, at full strength, with a long-haired bristle brush. For best results, apply by brushing Cetol in the direction of the grain.