How Do I Lay a Simple Garden or Retaining Brick Wall?

Laying a brick wall can be a satisfying weekend project — whether you're building a tidy garden border or a low retaining wall to hold back a sloped garden bed. With the right preparation, materials, and a bit of patience, many Kiwi homeowners can tackle a simple single-skin wall up to about 600–700 mm high. Anything taller, or any wall holding back significant soil loads, is a different matter entirely and will likely need professional input.

Understanding NZ Rules Before You Start

Before you mix a single batch of mortar, check whether your project needs a building consent. Under the NZ Building Code, retaining walls that retain more than 1.5 metres of ground generally require a building consent. Some councils have lower thresholds, so always check with your local council first. Garden walls that are purely decorative and freestanding are usually exempt, but it pays to confirm. The MBIE Building Performance website has clear guidance on exempt building work.

Planning Your Wall

Good planning saves headaches later. Consider:

• Purpose — Is it decorative, a garden border, or a retaining wall? Retaining walls carry soil loads and need more robust foundations and drainage.
• Height and length — Keep DIY retaining walls to under 600–700 mm for safety and simplicity.
• Location — Check for underground services (water, gas, electrical) before digging. Call Before U Dig (0800 248 344) — it's free and essential.
• Drainage — Retaining walls must have drainage behind them to prevent water build-up and wall failure. Plan for agricultural drain pipe and gravel backfill.
• Brick type — Use engineering bricks or concrete blocks for retaining walls (they're denser and more moisture-resistant). Standard clay facing bricks suit decorative garden walls.

Tools and Materials You'll Need

• Bricks or concrete blocks
• Cement, sand, and lime (or pre-mixed mortar)
• Spade and wheelbarrow
• Bricklaying trowel and jointing tool
• Spirit level and string line
• Rubber mallet
• Tape measure and builder's square
• Compactable gravel or crushed rock for the foundation
• Agricultural drain pipe and drainage gravel (for retaining walls)

You'll find most of these at Bunnings, Mitre 10, or PlaceMakers.

Step 1 — Dig and Prepare Your Foundation

A solid foundation is the most important part of any wall. Skipping this step is the number one reason DIY walls crack and lean.

• Dig a trench at least 200–300 mm deep (deeper in soft or clay-heavy soils, which are common in many NZ regions).
• The trench should be wider than your wall — roughly 1.5 times the wall's width.
• Fill with compactable gravel and compact it firmly, or pour a concrete footing (recommended for retaining walls and anything over 3–4 courses high).
• Allow concrete footings to cure for at least 24–48 hours before laying bricks.

Step 2 — Set Out Your String Line

• Use timber pegs and a string line to mark the face of your wall along its full length.
• Check it's level using a spirit level or laser level.
• This line guides every course of bricks and keeps your wall straight and true.

Step 3 — Mix Your Mortar

A standard mortar mix for garden walls is roughly 1 part cement : 1 part lime : 6 parts sand (by volume). Lime makes the mortar workable and slightly flexible, which helps in NZ's variable climate. Pre-mixed mortar bags are convenient for small jobs.

• Mix to a smooth, peanut-butter consistency — not too wet, not too stiff.
• Only mix what you can use in about 30–45 minutes.

Step 4 — Lay Your First Course

• Spread a bed of mortar about 10–12 mm thick on your footing.
• Press your first brick firmly into place, checking it's level in both directions.
• Butter the end of each subsequent brick with mortar before placing it (this is the perpend joint).
• Use a rubber mallet to tap bricks into alignment. Check level constantly.
• Stagger your joints — each course should offset by half a brick from the one below (this is called running bond and gives the wall strength).

Step 5 — Build Up the Courses

• Work up course by course, keeping your string line raised to each new level.
• Keep mortar joints consistent at around 10 mm.
• Check for plumb (vertical) regularly with your spirit level.
• Rake or tool your joints while the mortar is still slightly soft for a neat, weather-resistant finish.

Step 6 — Drainage and Backfilling (Retaining Walls)

For retaining walls, drainage is non-negotiable:

• Place agricultural drain pipe along the base of the wall behind it.
• Backfill with free-draining gravel (not clay soil) for at least 300 mm behind the wall.
• Leave weep holes (gaps in mortar joints near the base) every 1–1.5 metres to allow water to escape.

BRANZ has excellent technical resources on retaining wall construction and drainage best practice.

Mortar vs Dry-Stack: A Quick Comparison

When to Call a Professional

Some wall projects are firmly in tradesperson territory. Call a qualified bricklayer if:

• Your retaining wall will be over 600–700 mm high, or retains more than 1.5 m of soil.
• The site has poor or unstable ground conditions.
• You need a building consent — a licensed professional can ensure the work meets the NZ Building Code.
• The wall is near a boundary, structure, or underground services.
• You're unsure about any aspect of the design or drainage.

A licensed bricklayer will also know local council requirements and can produce compliant work. You can find qualified, reviewed bricklayers in your area at tradedirectory.co.nz.

Safety Notes

• Always call Before U Dig before digging.
• Wear gloves — wet mortar is caustic and can irritate skin.
• Lift bricks safely — they're heavy. Use your legs, not your back.
• Ensure any retaining wall is structurally sound before backfilling.

Sources & Further Reading

• MBIE Building Performance — Exempt Building Work
• BRANZ — Technical Resources for Homeowners
• Bunnings NZ — Bricklaying Supplies
• Mitre 10 NZ — Building Materials
• PlaceMakers NZ — Masonry Products
• WorkSafe NZ — DIY Safety