The only grouting that should be permitted in tall buildings would be in levelling up the tops of the concrete footings to receive the masonry courses, or in a very thin layer between the column pedestal and the masonry bed.
Mark the location of your footings - Your footings are where your posts will go.
Your deck plans will tell you where your footings should be placed.
Once your footings are marked, dig your post holes.
Are any pieces of playground equipment missing supports, anchors, or footings?