Laying bricks on a sloped surface is more challenging than working on flat ground, but it is achievable for a capable DIYer tackling smaller projects like garden edging, retaining borders, or a sloped pathway. However, for anything structural — retaining walls of significant height, foundations, or load-bearing work — you should seriously consider engaging a qualified bricklayer. NZ building consent requirements and the NZ Building Code may also apply depending on the scope of your project.
Understanding the Challenge of Sloped Surfaces
The main difficulty with a sloped surface is keeping your mortar joints level and consistent while the substrate beneath you is not. Gravity works against fresh mortar, causing it to slump or slide before it sets. Bricks can shift out of alignment, and if the base isn't properly prepared, the whole structure can become unstable over time — especially in NZ's variable climate with freeze-thaw cycles in colder regions and heavy rainfall in others.
Before you pick up a trowel, ask yourself:
- Is this a structural or decorative project?
- How steep is the slope?
- What is the finished height of the brickwork?
- Is drainage a consideration?
NZ Building Code and Consent Considerations
Not all brickwork requires a building consent, but some does. Under Schedule 1 of the Building Act 2004, certain low-risk work is exempt — but the exemptions have conditions. For example, a garden wall or decorative edging under a certain height may be exempt, while a retaining wall holding back significant soil may require consent or specific engineering input.
Always check with your local council before starting, as rules vary by region and site conditions (such as proximity to boundaries, slopes, or unstable ground). You can find general guidance at MBIE Building Performance.
Preparing the Base on a Slope
A solid, stable base is even more critical on a slope than on flat ground. Skipping this step is the most common DIY mistake.
- Excavate a level footing trench — even on a slope, your foundation should be stepped or levelled in sections (called a stepped footing).
- Use compacted hardcore or concrete as a base. For most garden brickwork, a concrete footing at least 100 mm deep is recommended.
- Ensure adequate drainage behind or beneath the brickwork to prevent hydrostatic pressure building up, which can push walls over. NZ's wet winters make this especially important — refer to BRANZ for guidance on drainage best practice.
- Check that the ground is stable and not prone to movement or erosion.
Stepping Your Courses on a Slope
The standard technique for bricklaying on a slope is to step the courses rather than trying to follow the angle of the ground.
How Stepped Footings Work
- Divide the slope into horizontal sections.
- Each section (or "step") should be level, with the step height equal to a whole number of brick courses (typically one or two courses per step).
- Overlap bricks at each step by at least half a brick length to maintain bond strength.
- Use a spirit level constantly — both horizontally and vertically.
This approach keeps mortar joints consistent and the structure stable. Trying to lay bricks at an angle to follow the slope is not standard practice and will result in weak, uneven work.
Mortar Mix and Application Tips
On a slope, mortar consistency is critical. Too wet and it will slump; too dry and it won't bond properly.
- A standard mix for general brickwork is 1 part cement : 1 part lime : 6 parts sand (by volume), though this varies by application.
- Work in smaller sections so mortar doesn't dry out or slump before you lay each brick.
- Butter each brick generously and press firmly, checking level after each placement.
- In hot or windy conditions (common in many NZ regions), dampen bricks slightly before laying to prevent the mortar drying too fast.
- Products from suppliers like Sika or Ardex include mortar additives and admixtures that can improve workability and adhesion.
You can source materials including cement, sand, and bricklaying tools from Bunnings, Mitre 10, or PlaceMakers.
Safety on Sloped Sites
Working on a slope introduces real safety risks. Unstable ground, heavy materials, and working at height (even modest heights) can cause serious injury. Keep these points in mind:
- Wear steel-capped boots and gloves — bricks and mortar are heavy and caustic.
- Ensure your working platform is stable. Don't balance on loose soil or uneven ground.
- Wet mortar is alkaline and can cause skin burns — wash off immediately if contact occurs.
- For any work involving excavation near boundaries or services, contact your local council and check for underground utilities.
Refer to WorkSafe NZ for general construction safety guidance.
When to Call a Professional
Some brickwork on a slope is firmly in professional territory. You should engage a qualified bricklayer if:
- The retaining wall will be over 1.5 metres in height (likely requires consent and possibly engineering sign-off).
- The slope is steep or the ground is unstable or clay-heavy.
- The brickwork is structural — part of a building, foundation, or load-bearing element.
- You're unsure about drainage, footings, or compliance with the NZ Building Code.
- The project is near a boundary, watercourse, or on a designated hazard-prone site.
Bricklaying is a skilled trade, and poor work on a slope can fail dangerously. A licensed bricklayer will also be familiar with Licensed Building Practitioners requirements for restricted building work. You can find qualified local bricklayers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
