Concrete pier blocks form a floating foundation for decks. A floating foundation rests on top of the ground rather than extending below grade. Below-grade foundations provide more stability than floating foundations and are less prone to shifting due to freeze and thaw cycles each year. However, the piers are simple to install and provide adequate stability for wood decks.
Mark the locations for the pier blocks by placing wood stakes at the corners of the planned deck. Connect the stakes with carpenter’s string to form the perimeter of the deck. Mark the locations of the piers, every 48 inches, along the strings with stakes or spray paint markers on the ground.
Excavate the sod from each pier location. The plant material in the sod will decay under the pier, which can cause settling of the deck. Fill the excavation with gravel and pack tight with a hand tamper.
Place the concrete piers on the gravel pads. Place a straight board between the piers and check the level with a 4-foot carpenter’s level. Roughly level the piers to within an inch or two of level by removing or adding gravel as needed below the piers.
Set a 1-foot segment of 4-by-4-inch treated post in the recess at the top of each pier. The concrete is shaped to accept this type of lumber. These posts will serve as the supports connecting the deck to the concrete pier foundation. Attach the frame of the deck to the post at the appropriate position to produce a level deck.
Lay a post base on top of the pier and mark the hole for the anchor bolt in the bottom of the post base onto the pier. Remove the bolt.
Drill a hole into the pier with a hammer drill that has a masonry drill bit.
Lay the post base back on top of the pier and line it up over the hole. Slide an anchor bolt into the hole and tighten it with an impact wrench.
Cut a 4-by-4 post to fit the length you need.
Slide the end of the post into the post base, lining up the post so it is flush with the post base.
Drive galvanized screws through the holes in the sides of the post base and into the post.
Dig a hole in the ground with the shovel where you need to place the first concrete pier. The hole needs to be at least 12 inches wide and 8 inches deep.
Add 1 to 2 inches of gravel to the bottom of the hole. This allows for the drainage of water.
Insert a fiberboard tube into the hole.
Mix the concrete in the wheelbarrow. Fill the fiberboard hole with the concrete using the shovel.
Apply a concrete bonding agent to the bottom of the first concrete pier with the paint brush.
Set the concrete pier on the poured concrete. Press down to set the concrete pier 1 to 2 inches into the concrete. Verify the pier is level by placing the level on top of the concrete pier.
Allow 4 to 6 days for the concrete to cure.
Repeat this process to set additional concrete piers in place.
Commercially available floats filled with materials such as expanded polystyrene foam (EPS) or syntactic foam provide more efficient flotation than air-filled floats. Syntactic foam and EPS have similar flotation characteristics and are available in various sizes capable of supporting between 450 and 4,754 pounds. Generally, floats should be positioned where you would place support posts if the floating dock were a deck in your yard, rather than a floating extension of your yard.
The dock is just like any other outdoor decking and can be any shape or size that pleases you. Remember, though, that the primary purpose is as a dock. It will have to have bollards or cleats on the water side to which boats can be secured.
Using cleats (available from any boating store or outlet) provides the most flexibility for docking, since they can be installed anywhere along the perimeter of the floating dock.
Mooring the Dock
A floating dock must be moored to the land lest it simply float away. The best mooring for the dock will be to two bollards---thick poles set into concrete in the ground, like the supports for a deck. On the deck itself, cleats attached to the end nearest the shore are tied to the bollards. The choices for mooring lines to hold the dock include nylon line, which stretches and can absorb shocks; polypropylene line, which floats, but will burst rather than stretch; and chain. Position the dock and moor the dock to the bollards.