Homeowners with a concrete surface outside their home already have a sturdy foundation for garden decking, but concrete, unlike soil, cannot easily be adjusted to create a level surface. Constructing the deck's frame first and then using the frame as a guide is the simplest way to lay garden decking on uneven concrete. For both ground-level and raised garden decks, a frame allows you to measure the height for underlying support beams that will make the deck surface level.
Measure and construct the garden deck's frame. Gather bricks and temporary support beams of various heights.
Lay the deck frame over the uneven concrete surface. If you're applying the deck directly over a concrete surface, use the bricks and temporary support beams to lift any sagging portions of the frame. If you're constructing a raised deck, adjust the frame's height and evenness using temporary support beams. For both types of deck, continue adjusting the supports until the surface of the deck frame is level.
Measure the height of each temporary support structure when the deck frame is level. Cut the support posts with a saw so they match the measurements of the temporary supports. Nail these supports into the concrete using a power hammer to drive rust-proof concrete nails into the surface.
Nail the deck frame onto the support beams. If portions of the deck frame are resting directly above concrete, use the power hammer and concrete nails to secure the deck frame directly to the concrete.
Finish the levelled deck surface: attach stringers to the frame and fasten decking to the stringers. Use the level on the finished surface to double-check the effectiveness of your supports.