lots of experience with sikkens

hello, im gettin ready to do a deck. i have a couple problems. 1st of all the weather. second is that the times that i have used sikkens dek i had to remove the old finish. now for this job im gonna sand to bare wood on the decks, but the railings have copper spindles. could i just clean the railings with old finish then go over it with the sikkens. the old finish looks like a regular deck finish (dry look) not shiny. the sikkens web site says that previous coating must be removed prior to application. is this only if the previous coating was sikkens? thanks painters