The present invention is a method for strengthening a vertical column, such as piles under piers and docks and for columns in bridges and buildings. A coiled FRP laminate is provided and wrapped in a helical fashion around the column, with the laminate overlapping itself. An epoxy resin coating is applied between the overlapping portions. The epoxy resin will then cure to form a substantially water tight shell. A plurality of spacers may be fixed to the column and adapted to hold the laminate a set distance away from the column. A plurality of sealing means is provided to seal the space between the shell and the column. A filler material may be pressurized to fill the space, penetrate cracks in the column, and displace water. Also, a plurality of rigid strengthening rods may be added between the column and the shell to further strengthen the column.