Easy DIY : Casting Modern Geometric Concrete Scented Candles With Custom 3D Printed Molds [Fusion 360 & STEP Files Included]

Combine raw brutalist architecture with warm ambient lighting. This project pairs a 3D-printed mold for casting a geometric concrete vessel with a hand-poured, natural lemongrass essential oil candle. The pure lemongrass oil provides a clean, invigorating citrus scent while naturally tinting the wax a pale pastel yellow.

For the Concrete Vessel:

1. 3D-Printed Mold: Outer twisted shell and inner cavity core (printed in PLA or PETG)
2. Cement/Mortar Mix: 1 part Portland cement to 2 parts fine sieved sand (or fine sand-topping mix)
3. Clean Water & Mixing Container
4. Flat Spatula / Trowel
5. Mold Release: Light coat of mineral oil, silicone spray, or cooking oil; Heat gun https://link.amazon/B011Jxor8
6. Protective Gloves & Dust Mask

For the Aromatic Candle:

1. Candle Wax: Soy wax flakes or paraffin wax (~100–150g depending on cavity volume)
2. Lemongrass Essential Oil: 100% pure (acts as both fragrance and natural yellow dye)
3. Candle Wick: Braided cotton wick with optional metal sustainer tab
4. Centering Tool: Precision tweezers or wooden wick bar
5. Melting Setup: Double boiler (heat-safe pitcher inside a water pot) and candy/infrared thermometer

3D Printing & Formwork:

1. 3D Printer: Creality Ender 3 S1 Pro (or any standard FDM machine)
2. Filament: PLA or PETG (Black or Grey)
3. Slicing Software: Cura, PrusaSlicer, or OrcaSlicer

1. Geometry: The mold consists of two mating elements: an outer faceted shell (twisted hexagon) and a central core plug that defines the round candle wax well.
2. Slicing Settings: Print with at least 4x0.4 or 2x0.8mmperimeter walls and 20–25% gyroid infill. Thin walls will flex outward under the hydrostatic weight of wet mortar, creating bowed sides.
3. Line Width - 0.8 mm Delivers massive layer bonding and thick, rigid mold walls
4. Wall Thickness - 1.6 mm Exactly 2 solid wall perimeters using a 0.8 mm line width
5. Infill Density - 20% Gyroid or Grid; prevents mold walls from bowing under wet cement
6. Supports - None (No Supports) Designed with self-supporting overhang angles
7. Print Speed - 160 mm/s Tested on the Ender 3 S1 Pro (tune to your printer's max stable speed)
8. Estimated Print Time - 2 hours 30 minutes Faster CoreXY printers can cut this under 1 hour 15 minutes Bambu Lab P1S Combo 500mm/s
9. Draft & Release: Ensure the inner plug has a slight taper (3°–5° draft angle) so it can be extracted cleanly without binding against the concrete once it begins to cure.

1. Dry Blend: Thoroughly blend dry cement and fine sieved sand in your mixing tub to ensure an even grey tone with no streaks.
2. Adding Water: Slowly fold in water until the mortar reaches a thick, packable slurry—similar to warm peanut butter. Avoid making it soupy, as excess water creates weak, dusty concrete and surface pinholes.
3. Pouring & Compacting:
4. Apply a light film of oil to the mold walls.
5. Pour the mortar into the mold gap around the central core.
6. Vibration: Firmly tap the mold against your work surface repeatedly. This brings trapped air bubbles up to the top and forces the slurry into sharp exterior ridges.
7. Screeding the Base: Use a flat spatula to scrape away excess mortar flush with the top rim of the mold, creating a level, wobble-free base for the pot.

1. Curing: Allow the mortar to cure undisturbed for 20 to 24 hours in a cool, shaded area.
2. Demolding: Carefully withdraw the inner round plug first, then peel or separate the outer shell segments.
3. Hydration Curing: Submerge the demolded piece in water for 24 to 48 hours to complete chemical hydration.
4. Surface Prep: Dry the concrete completely. If using a porous mix, apply a thin coat of water-based concrete sealer to the interior well to prevent melted wax from seeping through the walls.

1. Double Boiler Setup: Place your wax flakes in a heat-safe metal pouring pitcher and place it inside a saucepan filled with 1–2 inches of gently simmering water.
2. Melt: Heat the wax slowly until it liquefies completely (typically around 75°C to 80°C / 170°F to 175°F for soy wax).
3. Cool to Add Fragrance: Remove the pitcher from direct heat and let it cool to roughly 60°C – 65°C (140°F – 150°F). Adding essential oils to scorching-hot wax will burn off the delicate scent compounds instantly.
4. Infuse Lemongrass Oil: Stir in pure lemongrass essential oil at a ratio of 6% to 8% by weight (approx. 10–12 ml per 150 g of wax).
5. Stir gently and continuously for 2 minutes to ensure complete bonding.
6. The concentrated natural oil will transform the clear molten wax into a bright golden-citrus yellow without requiring chemical dye blocks.

1. Wick Placement: Dab a drop of hot glue, a wick sticker, or a bit of molten wax onto the bottom of the metal wick tab. Press it firmly into the dead center of the concrete pot's base.
2. Pouring: Slowly pour the warm yellow wax into the concrete cavity, leaving about 5–8 mm of clearance below the top concrete chamfer.
3. Wick Clamping: Lay a pair of stainless steel tweezers flat across the hexagonal rim of the concrete pot, clamping the flat cotton wick right at the center line. This keeps the wick completely straight and plumb as the wax contracts.

1. Slow Solidification: Let the candle sit on a level surface at room temperature for at least 4 to 6 hours. As it cools, the clear yellow liquid transforms into an opaque, buttery-yellow wax cake.
2. Wick Trim: Remove the tweezers and trim the excess braided wick to 5 mm (1/4 inch) above the wax line.
3. The First Burn: On your first light, let the candle burn continuously until the melted wax pool reaches all the way to the concrete rim (roughly 1.5 to 2 hours). This prevents "tunneling" and ensures an even scent throw for future burns.