Five-foot sandbox

• Check the species, grade and treatment tags. Use 1x6 floorboards, 2x10 walls and caps, and 6x6 posts. Reject cracked or warped parts. Store boards flat and spaced outdoors under cover for several days; wet floorboards before their final fit and reject persistent cupping.
• Choose a level site that drains after rain. Remove sod, roots and organic material. Prepare roughly 3 inches of compacted clean angular drainage aggregate with a level fine surface, extending past the box edges.
• Keep the bed edges at or above surrounding grade with an outlet for water. Every plank, wall and post needs uniform support. Relocate a ponding site; a stone-filled depression alone does not drain.

Check: The empty floor will have uniform ground support over its full area, and water can leave the bed.

• Cut eleven floor planks 60 in long. Rip F01 and F11 to 4 in width; keep F02-F10 at 5-1/2 in.
• Cut WS and WN 60 in long; cut WW and WE 57 in long. Cut P1-P4 from 6x6, each 9-1/4 in long.
• Cut four 17-1/2-in blanks from 2x10 for C1-C4. Mark the IDs from the cut list. Account for saw kerfs and trim damaged stock ends.
• Keep both wall widths and all wood thicknesses at their factory dimensions.

Check: All 23 parts are accounted for. The long walls are 60 in and the short walls are 57 in.

• On each cap blank, mark a 17-in baseline along the grain. Locate its midpoint 8 1/2 in from either end, and mark the opposite vertex 8 1/2 in perpendicular to it. Join the vertex to the baseline ends. Both equal legs must be 12 in.
• Clamp on sacrificial backing and cut safely. Test one cap on the frame before copying it. Round sharp exposed corners and ease edges while preserving flat wall/post bearing on the underside.
• The rounded 17-in baseline and 8-1/2-in rise leave a small trimming allowance. Check and trim both equal legs to 12 in, then dry-fit one cap before cutting the other three.

Check: Each cap has two 12-in equal legs, a 17-in diagonal, and its grain runs along that diagonal.

• Place WS and WN outside WW and WE to form a 60-in square. Place one uncut square 6x6 post inside each corner, flush with wall bottoms and tops.
• Clamp everything and compare diagonals, both about 84 7/8 in.
• Use eight T12350WP #12 x 3-1/2-in screws for each wall/post face. From the outside corner, mark lines at 4 and 6-3/8 in.
• On each, mark heights 3, 5-3/8 and 7-3/4 in above the floor underside. Add two holes on a 5-3/16-in line, at heights 4-3/16 and 6-9/16 in. For measurements from the wall bottom instead, subtract 3/4 in from each height.
• Follow the fastener layout drawing on this page. Install 64 total and recheck square.

Check: Posts touch both walls, no splits appear, all heads are flush, and the two frame diagonals agree.

• With enough adult helpers, support the heavy empty frame upside down on stable supports. Lay F01 and F11 at the outside edges and the other nine planks between.
• Use ten 1/4-in spacers. Align every plank end to the outside faces of WS and WN.
• Install four T08200WP #8 x 2-in screws per plank, 44 total. Each pair is 1-1/4 in from the plank side edges, on a line 3/4 in from its end.
• Drill 11/64-in clearance through the floor only, then 3/32-in pilot another 1-1/4 in into the wall. Countersink shallowly and set heads flush with a T20 bit. These hold the empty assembly together; never lift it filled.

Check: The floor is 60 in wide, all ten gaps are 1/4 in, and every screw enters a wall without splitting a plank end.

• Sand all touch surfaces, corners and cut edges. Treat new cuts and drilled holes with the compatible end-cut product, following its label.
• Allow it to dry fully. Apply an optional exterior finish only as its manufacturer directs.
• Turn the heavy empty box upright with enough adult helpers and place it on the prepared bed. Check for rocking and voids under planks; correct the bed. Wet the floor thoroughly and recheck that every drainage gap remains open after the boards have swollen.

Check: The floor bears evenly, cut treatment is dry, and water drains through open gaps without collecting in the box.

• Lay a single 7 x 7-ft sheet of permeable sand-retaining geotextile over the floor. Fold it up the walls and around the posts without cutting the corners.
• Keep it smooth and trim below the rim.
• Staple only above the intended 4-in sand line and seat every staple fully.
• Test the fabric with a small quantity of the chosen play sand and water. It must retain sand while letting water pass.
• Hose the lined box, then repeat with a shallow layer of sand. Check that water leaves through the fabric, plank gaps and bed without persistent pooling or steady sand loss. Correct any problem before filling.

Check: The fabric covers the whole floor, retains sand in the trial, drains freely and has no exposed staple points.

• Set each cap flat on both wall tops and its post, with the 12-in legs aligned to the outside wall faces. A small triangular corner of the square 6x6 post remains visible beyond the cap diagonal, 1-1/2 in below the cap top.
• Ease and treat that exposed corner; keep the full square post section. Correct any rocking before fastening.
• Use six T12300WP #12 x 3-in screws per cap. Local (u,v) positions are (3/4,3), (3/4,6), (3/4,9), (3,3/4), (6,3/4), (9,3/4), inches from the outside corner. Every screw enters wall sidegrain.
• Clamp the cap down, drill the pilot and shank lead hole as shown on the connection page, and set heads flush using T27.
• Install 24 total.

Check: All four caps bear firmly on walls and posts. Heads are flush and no screw tips or splits are exposed.

• Mark a 4-in depth above the floor, 5-1/4 in below the rim. Fill gradually with sand sold for children's play. The net volume is 7.24 cu ft after subtracting posts; 17 half-cubic-foot bags provide 8.5 cu ft, about 17 percent allowance.
• Stop at the depth line rather than using every bag. Watch for wall movement, leakage and trapped water as you fill. Correct drainage or loose parts before use.

Check: The sand is no deeper than 4 in, walls remain straight and the box is stable on its bed.

• Fit a removable cover for the 60-in square and secure it as its maker directs. Remove it completely for play.
• Keep the box covered when unused to limit animals and debris.
• Before each use, check for loose screws, splits, splinters, contamination and standing water. Repair damage and replace contaminated sand. Recheck after heavy rain and seasonal swelling. Supervise play, keep jumping off the caps out of use, and empty the sand before moving the box. Lift only the empty frame, never by its caps.

Check: The cover is removed for play, touch surfaces are smooth and tight, and the sand is clean and drained.