Install Fiberglass Shower Base Home › Forums › Public Forums › General Plumbing › Install Fiberglass Shower Base This topic has 1 reply, 2 voices, and was last updated 23 years, 7 months ago by Wallingford Plm+Htg. Viewing 1 reply thread Author Posts 14 Mar 2001 at 4:00 am #274763 MasterPlumbersKeymaster What would be the best method to install a fiberglass shower base on an uneven concrete foundation? Can the base be placed on a thin layer of mortar and leveled? 14 Mar 2001 at 9:07 pm #290405 Wallingford Plm+HtgParticipant Mark,Using mortar is a good idea for leveling and supporting.Try not to make the mix too wet as this will cause alot of shrinkage leaving voids. Author Posts Viewing 1 reply thread You must be logged in to reply to this topic. Log In Username: Password: Keep me signed in Log In