In the floor always use cat 4… This topic has 0 replies, 1 voice, and was last updated 12 years, 12 months ago by Karl Harrison Landscapes Ltd. Viewing 1 post (of 1 total) December 11, 2011 at 8:40 pm #228 Karl Harrison Landscapes LtdKeymaster Do you always use “Cat 4” treated posts when constructing your decking? Â Should we? Does it really matter? Author Posts Viewing 1 post (of 1 total) You must be logged in to reply to this topic. Log In Username: Password: Keep me signed in Log In