What tools do I need for build a custom steel fire pit for the backyard?

This guide includes a comprehensive tools list. Key welding & fabrication tools are detailed in the Tools Required section.

What thickness steel is best for an outdoor fire pit?

The ideal thickness for a custom steel fire pit is 3.0mm to 5.0mm mild steel plate compliant with AS/NZS 3678. Steel under 3.0mm warps rapidly under thermal expansion and burns through within one to two seasons, while 4.0mm plate delivers optimal longevity and heat retention without excessive weight.

Do you need to drill drain holes in a backyard fire pit?

Yes, you must drill at least three to four 10mm to 12mm drain holes in the base plate. Drainage holes prevent pooled rainwater from mixing with accumulated wood ash. Wet ash forms highly corrosive potassium hydroxide (potash lye), which rapidly rots mild steel base plates from the inside out.

What welding wire should you use for a mild steel fire pit?

Use 0.8mm or 0.9mm ER70S-6 solid MIG wire shielded with an Argon-CO2 mix (such as Argoshield 54), or 0.9mm E71T-11 gasless flux-core wire. For stick welding, run 2.6mm or 3.2mm E6013 general-purpose rutile electrodes or E7016 low-hydrogen rods on AS/NZS 3678 Grade 250 plate.

Can you weld Corten weathering steel to regular mild steel?

Yes, Corten weathering steel can be welded to standard AS/NZS 3678 Grade 250 mild steel using standard ER70S-6 wire or E7018 electrodes. However, the weld bead will lack Corten's atmospheric weathering properties and may rust faster unless capped with an AWS ER80S-G low-alloy filler wire.

How to Build a Custom Steel Fire Pit for the Backyard

Building a heavy-duty, custom steel fire pit is one of the most rewarding fabrication projects for an Australian backyard. Cheap imported sheet-metal fire pits burn through in a single winter, but a custom unit built from thick plate steel will handle high thermal cycling and last for decades. This

Quick answer

To build a custom backyard steel fire pit, cut six tapered side panels and a hexagon base from 3.0mm to 4.0mm AS/NZS 3678 Grade 250 mild steel plate. Bevel edges, tack the base assembly, fully weld the seams using 0.9mm ER70S-6 wire, and drill four 12mm drainage holes in the floor.

Skill level: Beginner to Intermediate
Time: 4 to 6 hours (plus paint curing time)
Trade: Welding & Fabrication
Updated: 6 November 2026

Tools you will need

MIG Welder
125mm
Magnetic Welding Clamps
Steel Ruler & Combination Square
Welding Chalk / Silver Streak Pencil
Slag Hammer & Wire Brush
Drill Press or Cordless Drill with stepped drill bit

🔥 Custom Steel Fire Pit Fabrication Guide

Why should you fabricate a custom steel fire pit rather than buy one?

Skill Level

Beginner to Intermediate — Estimated time: 4 to 6 hours (plus paint curing time)

What tools are required to weld a custom steel fire pit?

MIG Welder (180A–200A recommended) or Inverter Stick Welder (140A+) 125mm (5") Angle Grinder with ultra-thin metal cutting discs (1.0mm) and flap discs (40/60 grit) Magnetic Welding Clamps (45°/90° multi-angle arrows) Steel Ruler & Combination Square Welding Chalk / Silver Streak Pencil C-Clamps and Locking Pliers (Vise-Grips) Slag Hammer & Wire Brush (if stick welding) Drill Press or Cordless Drill with stepped drill bit (up to 12mm)

What steel grade and thickness are required for a fire pit?

Plate Steel: 3.0mm to 4.0mm mild steel plate (Grade AS/NZS 3678 - 250 or TruSpec). You will need approximately 1200mm x 1200mm total sheet area for a standard 600mm-wide fire pit (6 side panels + base). Legs: 40mm x 40mm x 3.0mm Equal Angle (EA) or 32mm NB Medium Pipe (approx. 1.2m total length cut into 3 or 4 legs). Welding Wire/Electrodes: MIG: 0.8mm or 0.9mm ER70S-6 solid wire with Argoshield 54 / 75/25 Ar/CO2 gas, OR 0.9mm E71T-11 gasless flux-core wire. Stick: 2.6mm or 3.2mm E6013 general purpose or E7016 low hydrogen electrodes. Finish: High-temp pot belly / engine enamel paint rated to 650°C+ (optional; raw steel patina is also popular).

What safety standards apply when welding plate steel in Australia?

⚠️ Safety is Mandatory on All Fabrication Projects:

PPE: Auto-darkening welding helmet compliant with AS/NZS 1338.1, heavy cowhide welding gloves, and non-flammable clothing (100% cotton drill or flame-retardant (FR) leather jacket/apron). Never weld in synthetic gear. Eye Protection: Clear impact safety glasses (AS/NZS 1337.1) worn under the helmet during grinding and prep. Ventilation & Fumes: Weld in an open, well-ventilated outdoor area or garage with extraction. Do not weld galvanised or zinc-coated steel without proper acid-stripping and respiratory protection (AS/NZS 1716 rated P2 fume respirator). Fire Safety: Clear a 10m radius of dry leaf litter, grass, and solvents. Keep a 4.5kg dry chemical ABE fire extinguisher or garden hose charged and ready on site.

Step-by-Step Guide

1️⃣ Design, Marking Out, and Plate Nesting

Plan a 6-sided tapered basket. Mark out six identical trapezoid side panels on your 3.0mm mild steel plate:

Top edge: 350mm Bottom edge: 200mm Vertical height: 250mm
Use a silver streak pencil or engineering scribe against a straight edge. Nest the cuts alternately (inverted) on the plate to minimise scrap and cut lines.

2️⃣ Cutting and Edge Preparation

Cut out the panels using your 125mm angle grinder fitted with a 1.0mm ultra-thin cutting disc. Run steady, straight cuts without twisting the disc in the kerf. Once cut:
Deburr all sharp edges with a 60-grit flap disc. Grind a 30° slight bevel on both inside and outside joining edges to ensure full root penetration. Clean back mill scale to bright, shiny bare steel at least 15mm back from every weld joint.

3️⃣ Marking and Cutting the Hexagonal Base

Place the cut panels upright on a flat steel bench to establish the internal hexagon profile, or calculate mathematically (an open hexagon with 200mm base sides). Mark out and cut the base plate from the same 3.0mm or 4.0mm plate.

Drill 4 to 6 evenly spaced 10mm to 12mm holes through the base plate using a stepped drill bit to allow water drainage and airflow for the fire.

4️⃣ Fit-Up and Tacking

Using magnetic squares, prop two side panels together on your workbench:
Set your MIG welder to: Voltage: ~18.5V–19.5V, Wire Feed Speed: ~6.0–7.5 m/min, Shielding Gas Flow: 12–14 L/min. (Stick alternative: 2.6mm E6013 at 75–85 Amps). Drop a solid 3–4mm tack weld at the bottom, middle, and top of the seam. Work your way around, tacking panel-to-panel until all six are aligned. Drop the base plate in from the top and tack it into place from underneath. Step back and verify symmetry. Tap any misalignment flush with a soft copper or ball-peen hammer before full welding.

5️⃣ Final Welding Sequence (Heat Management)

Do not weld all seams sequentially from top to bottom, or thermal expansion will twist the pit out of shape:

Run internal corner welds first using a stringer or slight stitch technique. Weld opposing sides (stitch 75mm runs, leap-frogging across the hexagon) to balance heat input. Weld the base plate to the side panels internally with intermittent 50mm stitch welds. Clean all slag or spatter thoroughly using a wire cup brush on an angle grinder.

6️⃣ Adding Feet and Elevation

Lifting the fire pit off the ground protects patio pavers and improves draw:

Cut three or four 150mm lengths of 40mm x 40mm x 3.0mm angle iron. Bevel the top ends to match the taper of your side panels. Tack, check level on a flat concrete surface, and fully fillet weld the legs to the bottom perimeter/base plate.

7️⃣ Surface Finishing and Burn-In

Wipe down the entire fire pit with wax and grease remover:
Option A (Painted): Apply two light, even coats of high-temperature pot belly black paint rated to 650°C. Allow 24 hours to air cure. Option B (Natural Patina): Leave bare for a rustic oxidised rust patina (do not coat in motor oil or toxic fluids). Initial Burn: Fire the pit gently with kindling for the first hour to cure the high-temp paint without blistering the finish.

Common Mistakes to Avoid

1.Skipping Drain Holes: Leaving out the base holes turns your fire pit into a rusty birdbath after the first rainfall, accelerating internal corrosion.

2.Welding Through Mill Scale: Attempting to weld directly over factory hot-rolled mill scale causes porosity, lack of fusion, and excessive spatter. Always grind to shiny metal.

3.Using Thin Sheet Steel: Using 1.0mm–1.6mm sheet metal will result in severe thermal warpage and burn-through within two seasons. Never build fire pits thinner than 3.0mm plate.

4.Running Continuous Heavy Welds in Order: Welding seams consecutively around the circle pumps too much heat into adjacent panels, causing the hexagon to pull out of round.

Pro Tips

💡 Root Gap Setup: Leave a 1.0mm to 1.5mm gap between your side panels during tacking (use a cut zip-tie or panel beater's wedge). This allows the weld pool to drop through to the back side for 100% penetration without beveling deep. 💡 Cardboard Template First: Make one panel template from corrugated cardboard or 3mm MDF. Test the angles on the bench before committing your angle grinder or plasma torch to expensive plate steel. 💡 Grip with Magnets: Use switchable magnetic clamps inside the corners; regular permanent magnets collect metal grinding dust that can contaminate your weld zone.

Recommended Tools
WIA Weldmatic 200i or Unimig Viper 185: Capable, versatile multi-process inverter welders suited for home fabricators handling up to 8mm plate. (Note: Commercial-grade welding machines over $1,000 can be financed through Local Knowledge Finance to preserve cash flow). Bosch GWS 9-125 125mm Angle Grinder: Reliable high-torque angle grinder built for heavy plate bevelling and mill scale stripping. Lincoln Electric Viking 3350 Auto-Darkening Helmet: Premium 4C optical clarity compliant with AS/NZS 1338.1 to keep your puddle visibility clear on out-of-position tacks.

Frequently asked questions

What is involved in build a custom steel fire pit for the backyard?: Building a heavy-duty, custom steel fire pit is one of the most rewarding fabrication projects for an Australian backyard. Cheap imported sheet-metal fire pits burn through in a single winter, but a custom unit built from thick plate steel will handle high thermal cycling and last for decades. This
What skill level do I need for build a custom steel fire pit for the backyard?: Beginner to Intermediate — Estimated time: 4 to 6 hours (plus paint curing time)
What are common mistakes when build a custom steel fire pit for the backyard?: 1. Skipping Drain Holes: Leaving out the base holes turns your fire pit into a rusty birdbath after the first rainfall, accelerating internal corrosion. 2. Welding Through Mill Scale: Attempting to weld directly over factory hot-rolled mill scale causes porosity, lack of fusion, and excessive spatter. Always grind to shiny metal. 3. Using Thin Sheet Steel: Using 1.0mm–1.6mm sheet me
What tools do I need for build a custom steel fire pit for the backyard?: This guide includes a comprehensive tools list. Key welding & fabrication tools are detailed in the Tools Required section.
What thickness steel is best for an outdoor fire pit?: The ideal thickness for a custom steel fire pit is 3.0mm to 5.0mm mild steel plate compliant with AS/NZS 3678. Steel under 3.0mm warps rapidly under thermal expansion and burns through within one to two seasons, while 4.0mm plate delivers optimal longevity and heat retention without excessive weight.
Do you need to drill drain holes in a backyard fire pit?: Yes, you must drill at least three to four 10mm to 12mm drain holes in the base plate. Drainage holes prevent pooled rainwater from mixing with accumulated wood ash. Wet ash forms highly corrosive potassium hydroxide (potash lye), which rapidly rots mild steel base plates from the inside out.
What welding wire should you use for a mild steel fire pit?: Use 0.8mm or 0.9mm ER70S-6 solid MIG wire shielded with an Argon-CO2 mix (such as Argoshield 54), or 0.9mm E71T-11 gasless flux-core wire. For stick welding, run 2.6mm or 3.2mm E6013 general-purpose rutile electrodes or E7016 low-hydrogen rods on AS/NZS 3678 Grade 250 plate.
Can you weld Corten weathering steel to regular mild steel?: Yes, Corten weathering steel can be welded to standard AS/NZS 3678 Grade 250 mild steel using standard ER70S-6 wire or E7018 electrodes. However, the weld bead will lack Corten's atmospheric weathering properties and may rust faster unless capped with an AWS ER80S-G low-alloy filler wire.

Written by Welder, the Welding & Fabrication specialist at VIC.Tools.