Determine the size of the sandbox, and cut the timbers using a circular saw. Remember that the corners of the sandbox will butt end to side, so subtract 3 1/2-inches (the true dimension of 4-by-4 timbers) from the desired length to allow for this.
Lay out the perimeter of the sandbox using the cut timbers. Remember to butt one timber's end to the next timber's side at the corners. Check that the corners are square with a framing square.
Mark the interior and exterior placement of the timbers with a shovel or spade. Set the timbers aside and dig a trench that is 6 inches deep and 4 inches wide along the pattern you just marked.
Fill the trench with 1 inch of sand and replace the first course of timbers, remembering to butt the end of one timber to the side of the next. Use a level and sledge hammer to check the level of the timbers. Once level, check the corners with a framing square to ensure perfectly square corners.
Lay the second course of timbers on top of the first course. The second course should run in the opposite direction as the first to create lapped corners. This will increase the stability of the sandbox frame.
Use a power drill to drive 6-inch timber screws through the second course and into the foundation timbers below at 3-foot intervals around the entire perimeter.
Cut the landscape fabric to the appropriate size and lay the fabric inside the sandbox. This will keep weeds from growing up through the sand. Leave enough fabric so that it covers the inside of the box and overlaps the second course of timbers.
Lay the third and final course of timbers on top of the second course and the landscape fabric. This will secure the landscape fabric in place. The third course should run in the opposite direction of the second course, creating lapped corner joints. Drive 6-inch timber screws through the top course and into the second course below at 3-foot intervals around the perimeter.
Trim the excess landscape fabric from the outer edge of the sandbox, and fill the sandbox with sand.
Measure and cut a piece of tarp that is 6 inches larger than the sandbox. Attach Velcro tape to the tarp and the perimeter edges of the sandbox. This will provide protection against rain, essentially giving you a waterproof sandbox.
Things You Will Need
- Circular saw
- 4-by-4 cedar timbers
- Framing square
- Shovel or spade
- Power drill
- 6-inch timber screws
- Landscape fabric
- Utility knife
- Velcro tape
- If the Velcro tape is not sticking properly to the tarp or timbers, staple the tape to the tarp using an everyday stapler. For the timber, you may have to use a heavy-duty staple gun. This will give you a more secure connection than most adhesives.