2-Tier Compost Bin

Dimensions

Cut list

Tools you'll need

• ✓

  Measuring Tape (5m or longer)

  Used for measuring all materials.

• ✓

  Pencil and Carpenter's Square

  For marking and confirming right angles.

• ✓

  Saw

  Using a home center's cutting service is recommended.

• ✓

  Electric Screwdriver

  An impact driver improves work efficiency.

• ✓

  Sandpaper

  Prepare two types: #120 and #240.

• ✓

  Level

  Essential for checking horizontal alignment during assembly.

• ✓

  Clamps (2 or more)

  Used for temporary fixation during joining.

• ✓

  Brush and Paint Tray

  Used for applying wood preservative.

Materials

Build steps

1. 1

   Confirm Materials and Tools

   ≈ 20 min

   Prepare 12 pieces of cedar board 19×120×900mm, 12 pieces 19×120×500mm, 4 corner posts 38×89×700mm, 1 bottom board 12×462×862mm, and 60 pieces of 65mm coarse-thread screws. For a two-layer design, it is recommended to purchase one additional middle partition board approximately 12×462×862mm. Tools include electric screwdriver, circular saw, measuring tape, carpenter's square, sandpaper (#120/#240), two F-clamps, level, and two hinges.

   Measure

   W 900 mm

   MeasureSTEP 1 / 22

   Tip

   • The two-layer design separates areas with a middle partition board, allowing management of fully matured compost and new input separately.
   • Boards 900mm long tend to warp easily; check flatness by laying flat when purchasing.

   Watch out

   • 900mm cedar boards are prone to break during transport; carry them flat or bundle two together in a vehicle.
   • 60 screws are barely sufficient for two-layer setup; purchasing an extra 10 screws as a reserve is advisable.
2. 2

   Prepare the Work Space

   ≈ 10 min

   Secure a flat workspace of 2.5m by 2m. To handle 900mm long materials, a larger space than compost-1 is needed. Arrange two workbenches side by side so boards up to 900mm can be placed flat edge to edge. Lay a blue sheet to collect wood chips.

   Inspect

   No wobble ✓

   InspectSTEP 2 / 22

   Tip

   • Handling 900mm boards alone makes balancing difficult; enlist help if possible.
   • If the workbench edge is only 900mm, the board may fall during cutting; prepare extra supports.

   Watch out

   • Working in a narrow space risks damaging boards when flipping them; maintain at least 900mm clearance.
   • Poor ventilation causes sanding dust to impair visibility; outdoor or garage work is recommended.
3. 3

   Mark Cutting Lines on Materials

   ≈ 25 min

   Use carpenter's square and pencil to mark all cutting lines. Label the back side of front/back boards (900mm) and side boards (500mm) as 'Front (900)' and 'Side (500)' respectively to avoid confusion. Mark top and bottom on the four posts. For two-layer, mark the middle partition position at center width (450mm) on inside faces of front/back and side boards.

   Mark a line

   Use a try square

   MarkSTEP 3 / 22

   Tip

   • Use a soft pencil (2B or softer). For long lines, stretch a string tightly between two points before marking to avoid wobble.
   • Two-layer partition doesn't have to be symmetrical; making the fermentation area larger and the mature area smaller is also possible.

   Watch out

   • Confusing 900mm and 500mm markings causes waste; verbally confirm measurements before marking.
   • Not marking the partition position clearly on all boards makes positioning impossible during assembly.
4. 4

   Cut Front and Back Boards (900mm x 12 pcs)

   ≈ 35 min

   Cut 12 cedar boards to 19×120×900mm. Using a home center cutting service is practical (30-50 yen per piece, total under 600 yen). For self-cutting, use a circular saw and right angle guide. Since 900mm length may exceed saw capacity, cut from both ends meeting in the middle if necessary.

   Cut

   Use the in-store cut service

   CutSTEP 4 / 22

   Tip

   • Home center cutting is accurate within ±1mm and more reliable; ordering all 12 at once saves time.
   • When cutting, cut on the waste side of the marked line, accounting for 2mm blade thickness.

   Watch out

   • Cutting 900mm boards by hand saw tires the hand and reduces accuracy in later cuts; use circular saw or cutting service.
   • If one board is cut shorter, repurpose it as the two-layer partition board (462mm); do not discard.
5. 5

   Cut Side Boards (500mm x 12 pcs)

   ≈ 25 min

   Cut 12 cedar boards to 19×120×500mm. The process is similar to front/back boards but shorter in length. Bundle 4 boards and clamp together for batch cutting. Check right angle carefully on first board, then use as reference for others.

   Cut

   Use the in-store cut service

   CutSTEP 5 / 22

   Tip

   • Bundling four boards and cutting at once saves time.
   • At 500mm length, handling is easier and cuts tend to be more accurate.

   Watch out

   • Stop immediately if blade binds when batch cutting; forcing may cause kickback.
   • Uneven side board lengths cause warping during assembly; keep within ±1mm.
6. 6

   Cut Corner Posts and Bottom Board

   ≈ 25 min

   Cut four 2×4 lumber posts (38×89mm) to 700mm length. Cut the lauan plywood bottom board (12mm) to 462×862mm (inner dimensions: 500 - 19*2 = 462, 900 - 19*2 = 862). Mark orientation with an arrow since the rectangle has specific front/back (862mm) and left/right (462mm) directions.

   Cut

   Use the in-store cut service

   CutSTEP 6 / 22

   Tip

   • Clamp four posts together and cut simultaneously for uniform length.
   • Mark 'front-back' and arrow on bottom board immediately after cutting to avoid confusion.

   Watch out

   • If one post is cut at an angle, recut others to match; uneven lengths prevent assembly.
   • If bottom board is cut reversed, it becomes scrap; refer to written dimensions during cutting.
7. 7

   Sanding All Materials (#120)

   ≈ 60 min

   Since there are many materials (24 cedar boards + 4 posts + 1 bottom board), using an orbital sander is strongly recommended. Remove burrs and splinters with #120 grit, sanding along the grain. Manual sanding takes about 2 hours, with a sander around 45 minutes.

   Sand

   #120

   SandSTEP 7 / 22

   Tip

   • Let the sander weight do the work; pressing hard causes surface damage.
   • Orbital sanders costing around 3,000 yen are affordable and useful for ongoing DIY.

   Watch out

   • Spending too long on a single board delays overall progress; aim for under 5 minutes per board.
   • Replace sandpaper when clogged; using worn paper wastes time and reduces efficiency.
8. 8

   Finishing Sanding (#240)

   ≈ 35 min

   Finish sanding all surfaces with #240 grit until no roughness is felt. Because the 900mm front/back boards have extended height, run your hand over the top edges to detect any unevenness. After sanding, wipe dust with a damp cloth and allow to dry for 10 minutes.

   Sand

   #240

   SandSTEP 8 / 22

   Tip

   • Slide your palm over boards; no catches means sufficient sanding.
   • Edge grain (short board ends) absorbs moisture and preservative more, so sand these areas thoroughly.

   Watch out

   • Remaining sanding dust causes blotchy finish during painting; ensure thorough wiping.
   • Over-sanding edges rounds corners and causes gaps during assembly; keep corner rounding minimal.
9. 9

   Temporary Assembly and Right Angle Check of Posts

   ≈ 25 min

   Stand four corner posts upright on the workbench, arranging them to form a 900×500mm rectangle. Use carpenter's square to confirm each corner is 90°, then clamp for temporary fixation. Measure diagonal length to be 1091mm (√(900²+500²)); within ±3mm is acceptable.

   Level the ground

   FoundationSTEP 9 / 22

   Tip

   • Diagonal measurements of a rectangle should be equal; differences indicate distortion.
   • The 900mm long side tends to flex; check for sagging by pressing center during temporary assembly.

   Watch out

   • Proceeding with a right angle error over 3mm causes over 10mm distortion later; correct it here.
   • The shorter 500mm side distorts more easily; fix it before defining the 900mm side.
10. 10

    Drilling Pilot Holes in Posts

    ≈ 30 min

    Drill φ3.5mm pilot holes at all screw positions. Each post has 6 rows × 2 sides = 12 holes; total 48 holes. If using a middle partition, add 4–8 pilot holes for it.

    Drill a hole

    φ3.5mm

    DrillSTEP 10 / 22

    Tip

    • Wrap masking tape on drill bit at 30mm depth as a depth guide.
    • Start drilling vertically to maintain angle and depth when bit contacts 2×4 lumber.

    Watch out

    • Screwing without pilot holes splits 2×4 lumber; always drill pilot holes first.
    • If a hole is drilled incorrectly, fill with wood filler and proceed; it's not noticeable.
11. 11

    Attach First Layer of Front and Back Boards

    ≈ 30 min

    Attach the 900mm front/back boards at the lowest tier to the posts with 65mm coarse-thread screws. Align bottom of board flush with bottom of post, sandwiching between two posts. Use two screws per joint, total of 8 screws. Two-person work is ideal due to board length; one person can clamp temporarily before screwing.

    Drive screws

    コーススレッド 51mm

    ScrewSTEP 11 / 22

    Tip

    • Holding 900mm boards level alone is difficult; clamp one side for support.
    • After loosely fastening the first screw, reconfirm right angle before final fastening of second screw.

    Watch out

    • If long boards sag in the center during assembly, the finished box will be warped; support center when clamping.
    • Bent screws must be removed and repositioned about 5mm away; angled screws cause visible distortion.
12. 12

    Attach Front and Back Boards for Layers 2–5 (Maintain Ventilation Slots)

    ≈ 50 min

    Stack boards from the second layer upward atop the first, securing them while maintaining 5mm gaps for ventilation slots. Use 5mm plywood offcuts as spacers to keep even gaps. Each side requires six layers (120×6=720mm; box height is 700mm plus over 20mm excess), so top boards will protrude beyond posts.

    Drive screws

    コーススレッド 51mm

    ScrewSTEP 12 / 22

    Tip

    • Make three 5mm spacers to place at ends and center for parallel alignment.
    • Place boards with convex warp side up so assembled box appears straight.

    Watch out

    • Boards 900mm long warp easily; use warped boards on lower or middle tiers to reduce visual impact on top.
    • Ventilation slots over 6mm do not affect composting; don't worry about perfect spacing.
13. 13

    Attach Topmost Front and Back Boards and Middle Partition (Optional)

    ≈ 30 min

    Attach the topmost front and back boards. If constructing two layers, insert middle partition board at center (450mm) position by fixing it with screws to front/back boards and bottom board. Partition height equals box height (700mm).

    Drive screws

    コーススレッド 51mm

    ScrewSTEP 13 / 22

    Tip

    • Making partition removable eases compost turning.
    • Alternatively, use a 12mm thick plywood board that slides into slots for flexible two-layer switching.

    Watch out

    • Screwing partition fixedly makes compost turning difficult; consider dowel and pin for removable fit.
    • If unable to place partition centrally, omit it and use as a single-layer box.
14. 14

    Attach Side Boards (Both Left and Right)

    ≈ 40 min

    Attach 12 side boards (500mm) to both left and right sides similarly to front/back boards. Overlap the ends over front/back boards, maintaining 5mm ventilation gaps per layer. Side boards are short and manageable for single-person work.

    Build the frame

    Check for square

    AssembleSTEP 14 / 22

    Tip

    • Side boards are easier to handle due to 500mm length; both sides can be assembled quickly.
    • Apply a small amount of wood glue on joint faces with front/back boards to improve airtightness.

    Watch out

    • If distortion occurs in middle layers after side boards attach, redrill pilot holes and adjust.
    • If side boards protrude past posts, shave post sides to fit; do not force boards in.
15. 15

    Diagonal Measurement Check and Distortion Correction

    ≈ 20 min

    After attaching all wall boards, measure diagonal lengths of the top surface. The theoretical length is 1091mm (√(900²+500²)). Less than 3mm difference is acceptable. Larger deviations require clamping to force alignment, adding angled screws for fixation. Rectangles distort more easily than squares, so check carefully.

    Check level

    Level ✓

    LevelSTEP 15 / 22

    Tip

    • Press the corner opposite the longer diagonal to correct distortion.
    • Rectangles tend to distort along the long edge; check 900mm side center with a level and adjust.

    Watch out

    • Distortion over 5mm requires partial disassembly and repositioning of screws.
    • Screws used for correcting distortion should be hidden before painting.
16. 16

    Drill Ventilation Holes in Bottom Board

    ≈ 25 min

    Drill twelve φ20mm ventilation holes on the bottom board (462×862mm) arranged in 3 columns by 4 rows, keeping 50mm or more from edges. For two-layer boxes, split six holes per side of the partition for even fermentation.

    Drill a hole

    φ20mm

    DrillSTEP 16 / 22

    Tip

    • Use hole saw for one-step drilling. For drill bits, place wood block under rear to prevent tear-out.
    • Mark all 12 holes with pencil before drilling to avoid mistakes.

    Watch out

    • If edge cracks, repair with wood filler; no effect on ventilation.
    • Hole position deviations have minor impact on fermentation; prioritize the number of holes.
17. 17

    Attach Bottom Board

    ≈ 25 min

    Insert bottom board inside box bottom, securing it around perimeter to post feet with six 65mm coarse-thread screws (three front and three back). For two-layer boxes, add two screws at partition position.

    Lay the top board

    5mm 間隔

    Top boardSTEP 17 / 22

    Tip

    • Bottom board designed to fit snugly inside box; shave corners slightly if necessary.
    • Applying wood preservative to bottom board top surface before installation makes the process easier.

    Watch out

    • Fill gaps between bottom board and sides with wood glue to prevent insect entry.
    • If bottom board warps, reinforce connection with L-brackets attaching to posts at center.
18. 18

    Make Lid (900×500mm)

    ≈ 45 min

    Make a lid by joining 4 leftover cedar boards 900mm long side by side with 65mm coarse-thread screws to approximate dimensions of 900×500mm. Attach three scrap reinforcements on backside (both ends and middle). Tilt one side 5mm higher to allow rainwater runoff. For two-layer boxes, making lid in two parts is convenient.

    Lay the top board

    5mm 間隔

    Top boardSTEP 18 / 22

    Tip

    • Two-layer lids divided in the middle allow opening one side for compost input.
    • Applying water-repellent paint on lid surface causes rainwater to bead and run off.

    Watch out

    • If lid is too heavy to open easily, add handles such as inexpensive metal ones from 100-yen shops.
    • If lid warps, reverse direction and apply weight and moisture to correct shape.
19. 19

    Attach Hinges and Lid

    ≈ 25 min

    Attach two stainless steel hinges (four if two-layer) connecting lid to topmost front/back board top surface. Position hinges 100mm inside lid edges. Drill φ2mm pilot holes for supplied screws before tightening. Test lid opening and closing.

    Drive screws

    コーススレッド 51mm

    ScrewSTEP 19 / 22

    Tip

    • Always use stainless steel hinges; iron hinges rust within a year and seize.
    • Installing a lid stopper (chain) prevents lid from tipping backward and increases safety.

    Watch out

    • If hinge placement is incorrect and lid doesn't close, fill holes with wood filler and reposition.
    • If screw holes become stripped, fill with toothpick and glue, then retry.
20. 20

    First Coat of Wood Preservative

    ≈ 55 min

    Apply outdoor wood preservative (e.g., Xyladecor, Non-Rot) on all interior and exterior surfaces. Recommended brush width: 30–50mm. Pay attention to end grain and corners. The first coat should be thin for penetration. The surface area is approximately 3 square meters; 500ml preservative is sufficient. Dry for 24 hours.

    Waterproof

    Two coats required

    WaterproofSTEP 20 / 22

    Tip

    • 500ml preservative typically covers about 3㎡, matching this size (2.8㎡).
    • Wash brushes with special thinner after use for reusability.

    Watch out

    • Wipe any drips from the ground before drying; dried stains are hard to remove.
    • Any uneven finish in first coat can be covered in second coat; avoid stress on perfect finish.
21. 21

    Second Coat of Wood Preservative

    ≈ 50 min

    After the first coat is fully dry, apply a second coat somewhat thicker to eliminate unevenness. End grain absorbs a lot; three coatings are acceptable. Dry 24 hours. Thicker coating prolongs durability.

    Waterproof

    Two coats required

    WaterproofSTEP 21 / 22

    Tip

    • Apply the second coat in temperatures above 15°C and humidity below 70%.
    • Multiple coatings (third coat) can be applied on areas desired for extra durability after drying.

    Watch out

    • Cover with blue sheet if rain approaches to prevent whitening.
    • Clean the brush with thinner if it starts to harden before continuing.
22. 22

    Place Compost Box and Final Check

    ≈ 25 min

    Carry finished two-layer compost box to installation site with good sunlight and ventilation. Due to 900mm size, two people are recommended for transport. Level the ground and add gravel if necessary. Check lid operation, re-tighten all screws, and inspect for any looseness before completing.

    Done!

    Done — nice work!

    DoneSTEP 22 / 22

    Tip

    • Use layers to separate fermented and new input sides; turning compost once per week suffices.
    • Placing on southeast side accelerates fermentation; avoid north side.

    Watch out

    • Direct ground placement accelerates bottom decay; raising 5cm on bricks doubles durability.
    • Due to wide bottom area (900×500mm), watch for bottom board warping; inspect every 3 years.

Warnings

• ⚠️If used outdoors, applying wood preservative is essential (reapplication recommended annually).
• ⚠️Use stainless steel screws (iron screws will rust).
• ⚠️Drill pilot holes before screwing to prevent wood splitting.

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