Self-watering planter
Cut at two-thirds height, invert the neck into the base as a reservoir, roll the rim in 70 °C water and sand to 3000 grit. One bottle, one hour.
From bin to workbench
A used PET bottle becomes a planter, a scoop or a desk tidy; a corrugated box becomes drawer dividers, coasters or a storage cube. Two numbers decide success: the resin code stamped in the triangle on the base, and the flute thickness hiding inside the cardboard. This guide covers both, then walks one build — a bottle planter — from first cut to a polished rim.
01
Read the triangle on the base before anything else. Codes 1, 2 and 5 — PET, HDPE and PP — are the workable trio and the ones most kerbside rounds accept. Everything else goes back in the bin.
02
PET softens at 70–80 °C, so a dip in water at about 70 °C makes a bottle wall pliable enough to roll a rim or square a shoulder by hand. No oven, no flame, no fumes.
03
Edges become finished through a fixed grit ladder: 400, 800, 1500, then 3000, with water as lubricant and polishing compound at the end. Skip a grade and the scratches survive.
Stick to resin codes 1, 2 and 5 — PET, HDPE and PP, the same trio most kerbside rounds collect.
Every rigid container carries a resin identification code: a number from 1 to 7 inside a chasing-arrows triangle, moulded into the base. Code 1 is PET (drink bottles), 2 is HDPE (milk and detergent jugs), 3 is PVC, 4 is LDPE, 5 is PP (yogurt tubs), 6 is PS, and 7 is a catch-all for mixed and layered plastics.
The bench trio is 1, 2 and 5. They are consistent polymers, easy to identify, and accepted by most kerbside collections — so offcuts go back into the recycling stream instead of landfill. Code 7 is the one to avoid: because it covers mixed materials, its behaviour under a knife or in warm water cannot be predicted.
Only PET has the crafter's trick: a glass transition at about 70–80 °C. Water at roughly 70 °C softens the wall for hand-shaping while staying far below melting — which is why this guide works with a jug of hot water, never an oven or a flame. The full code-by-code breakdown is on the Recycling Codes 1-7 for Craft Materials page.
Cut at two-thirds height, invert the neck into the base as a reservoir, roll the rim in 70 °C water and sand to 3000 grit. One bottle, one hour.
A milk jug's handle is already moulded; cut diagonally below it and the body becomes a scoop. Code-2 HDPE cuts cleanly and needs only the 400 and 800 grit passes.
Single-wall board at about 2.5 mm slots together with half-lap joints to grid a drawer. Cut with the flute running vertically so the divider resists sideways crush.
Thin flutes at 1.6 or 0.8 mm laminate into a flat blank that takes a UV-resin top coat. Build the coat in layers under 3–5 mm, curing 1–5 minutes each.
Two stacked flutes give appliance-box board near-timber rigidity. Score folds on the outside face, tape the corners, and the cube carries books without bowing.
Code-5 tubs arrive watertight with rolled rims. Trim to height, sand the cut edge through the grit ladder, and they organise screws and brushes for years.
At 70 °C a bottle stops being packaging and becomes a material.
The flute size printed nowhere on the box decides what the box can become.
| Material or step | Number | Unit | What it decides |
|---|---|---|---|
| PET bottle (code 1) | 70–80 | °C | glass transition — the softening band for hand shaping |
| Shaping water | about 70 | °C | hot enough to soften PET, never near melting |
| Flute A board | 4.7 | mm | thickest standard flute; cushioning and structure |
| Flute C board | 3.6 | mm | general-purpose shipping-box stock |
| Flute B board | 2.5 | mm | crush-resistant walls for boxes and dividers |
| Flute E board | 1.6 | mm | smooth faces for models and laminating |
| UV resin layer | 3–5 | mm maximum | thicker pours stay tacky in the middle |
| UV cure time | 1–5 | min per layer | under a 365–405 nm lamp |
The list names the standards and regulations behind each figure; no commercial source is cited.