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Set and Level Four Corners of Blocking
Set the four corners for the deck. Digging about 6 inches into the ground, create holes for the blocks so you can adjust (raise or lower) to make them even. The blocks should be spaced to make a 7' x 19' rectangle, leaving about 6 inches from each block for deck boards to add another 8' x 20' rectangle. Using a string level or laser level, make sure each block is level. Or, check if corner blocks are level by running a straight board through the divots in corner blocks and checking with a level.
Create Lines for Interior Blocks
Measuring 2 feet from corners, spray paint a straight line down the short portion of the deck; this is the line for the interior blocks. Spray another line 2 feet between two interior lines. You should have three horizontal lines. Dig a 6-inch trench along the lines. Then dig a trench between your corner blocks.
Set and Level Interior Blocks
Space four interior blocks 2 feet apart from one another on each trench line. Level the interior blocks to your corner blocks. You will have two blocks between your horizontal corners and three blocks between your vertical corners.
Continue Setting Outer Blocks
Blocks should be equally spaced. Set them and make sure they're level, using wet concrete mixed in a large wheelbarrow, adding or removing concrete as necessary. A good way to check that all blocks are lined up is by using a straight piece of board and setting it through the X indentation of each block and see how they line up. Let dry. Make sure the concrete has set before moving to next steps.
Lay the Pressure-Treated Deck Joists
Making sure everything is level, lay the 2" x 6" deck joists on edge inside the deck blocks. Measure from each 2x6 to make sure they are evenly spaced, 2 feet apart.
Begin Laying Synthetic Deck Boards
Place one board in the middle of the deck area, making sure it hangs evenly off each end of the 2x6s. The deck planks are made to have a gap between them, so use a small nail as your spacing guide at each joint. Where the deck plank meets each joist, screw two square-head trim screws 1-1/4 inch from each side of the deck plank. Don't use a lot of pressure because the thread will pull the screw down. Hammer the screws down a bit so they don't stick up. Repeat on each plank. This process should move fairly quickly.