Welding a steel letterbox post is one of the more approachable DIY welding projects a homeowner can tackle. It doesn't involve any restricted or licensed work, there's no building consent required, and the materials are inexpensive and easy to source from your local hardware store. That said, welding does carry real safety risks, so good preparation is essential before you strike an arc.
Is This a DIY-Friendly Job?
Absolutely — welding a letterbox post is low-stakes compared to structural or pressure welding. You're typically joining mild steel sections (such as RHS — rectangular hollow section — or round tube) to create a simple post-and-bracket assembly. No special certification is required for this kind of non-structural, decorative metalwork on your own property. However, if you've never welded before, this project is still a reasonable starting point, provided you take the time to practise on scrap steel first.
Equipment You'll Need
- Welder: A small MIG (GMAW) welder is the most beginner-friendly option for mild steel. Entry-level MIG welders are available at Bunnings and Mitre 10. Stick (MMA) welders also work well outdoors. TIG is overkill for this job.
- Welding wire or rods: For MIG, use ER70S-6 wire (0.6 mm or 0.8 mm) with mild steel. For stick, E6013 rods are forgiving for beginners.
- Shielding gas: MIG welding requires a CO₂/Argon mix (commonly C25 — 75% Argon, 25% CO₂). You can hire or buy gas bottles from welding suppliers.
- Angle grinder: For cleaning welds, cutting steel to length, and grinding back any rough beads.
- Steel: Mild steel RHS or CHS (circular hollow section) from a steel merchant or PlaceMakers. A typical post might be 40×40 mm or 50×50 mm RHS.
- Clamps and a welding table or flat surface: To hold pieces square while you tack-weld.
- Measuring and marking tools: Square, tape measure, soapstone or marker.
Personal Protective Equipment (PPE)
Safety is non-negotiable. WorkSafe NZ sets out clear expectations around hazardous work, and welding produces UV radiation, fumes, spatter, and intense heat.
- Auto-darkening welding helmet (minimum shade 10 for MIG)
- Welding gloves — leather, gauntlet-style
- Flame-resistant clothing — no synthetics; wool or cotton is best
- Steel-capped boots
- Welding fume respirator if working in an enclosed space
- Fire extinguisher nearby
Always weld in a well-ventilated area. Outdoors is ideal for a small job like this. Keep flammable materials well clear of your work area.
Step-by-Step: Welding Your Letterbox Post
1. Plan and Cut Your Steel
Decide on your post height (typically 900–1,100 mm above ground for a standard letterbox), cut your steel to length with an angle grinder or drop saw, and deburr the ends.
2. Clean the Steel
Weld quality depends heavily on clean metal. Remove mill scale, rust, paint, or galvanising from the weld area using an angle grinder with a flap disc. Never weld galvanised steel without removing the zinc coating first — zinc fumes are toxic.
3. Fit Up and Tack Weld
Clamp your pieces in position and check for square with a combination square. Place small tack welds at two or three points to hold the assembly before running full beads.
4. Run Your Welds
For a letterbox post bracket, a single-pass fillet weld around the joint is typically sufficient. Aim for consistent travel speed and keep your torch angle at roughly 10–15° from vertical (for MIG). Let each weld cool before moving on.
5. Clean and Inspect
Chip slag (if stick welding), then grind or wire-brush the weld. Look for obvious defects like porosity or undercut. For a letterbox post, cosmetic welds are fine — this isn't a structural application.
6. Rust Protection and Finishing
Mild steel will rust quickly in the NZ climate, especially in coastal areas. After welding, apply a zinc-rich primer followed by a topcoat. Resene and Wattyl both offer suitable metal primers and topcoats. Alternatively, have the post powder-coated by a local finisher for a durable, professional result.
7. Installation
Set the post in concrete at least 300–450 mm deep, depending on soil conditions. Check it's plumb before the concrete sets.
A Note on Galvanised Steel
If your letterbox post or bracket is galvanised, do not weld it without grinding back the zinc coating in and around the weld zone. Zinc fumes cause metal fume fever and can be seriously harmful. If you must weld near galvanised sections, use a P2 respirator rated for metal fumes and work outdoors.
When to Call a Professional
While this is a DIY-friendly project, there are situations where it's worth calling a qualified welder:
- You have no welding experience and don't want to invest in equipment for a one-off job
- The design involves more complex fabrication (e.g., decorative ironwork, multiple brackets)
- You want a high-quality finish that will last decades without maintenance
- You're working with stainless steel or aluminium, which require different processes and more skill
A professional welder can often knock out a simple letterbox post in an hour or two. You can find qualified local welders on tradedirectory.co.nz.
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