A well-built retaining wall can last for decades — but only if it receives some basic ongoing care. The good news is that most routine maintenance is straightforward and something you can do yourself. Knowing what to look for, and when to call in a professional, will protect both your property and your investment.
Why Maintenance Matters
Retaining walls hold back significant volumes of soil and, in wet conditions, water-saturated ground can exert enormous pressure. In New Zealand, where we experience everything from heavy rainfall in the west to expansive clay soils in many suburban areas, neglected walls can fail — sometimes suddenly. A failing wall can damage fences, foundations, driveways, and neighbouring properties, and may create a safety hazard. Regular maintenance keeps small problems from becoming expensive ones.
Drainage: Your Most Important Check
Drainage is the single biggest factor in retaining wall longevity. Most walls are built with drainage aggregate and weep holes (small openings near the base) or a subsoil drain behind them to relieve hydrostatic pressure. If these become blocked, water builds up behind the wall and the pressure can cause bulging, cracking, or outright collapse.
What to do:
- After heavy rain, check that weep holes are flowing freely. If water isn't coming out during or after a downpour, they may be blocked.
- Clear any mud, moss, or debris from weep holes using a piece of wire or a garden hose.
- Make sure surface water around the top of the wall drains away from the retained soil, not towards it.
- Check that any surface drains or channels nearby are clear of leaves and silt.
BRANZ has useful guidance on drainage requirements for retaining structures if you'd like to understand the technical background.
Visual Inspections: What to Look For
Do a walk-around inspection at least twice a year — ideally in autumn before the wet season and again in spring. After any significant storm or earthquake, do an extra check.
Look for:
- Cracks in concrete, masonry, or timber — hairline cracks may be cosmetic, but horizontal cracks or cracks that are widening are a warning sign
- Bulging or leaning — any outward movement of the wall face needs professional assessment promptly
- Settlement at the base or behind the wall (sunken ground, tilting posts)
- Rust staining on concrete walls, which can indicate corroding reinforcing steel inside
- Rotting timber on timber-crib or sleeper walls — probe with a screwdriver; soft spots mean the timber is compromised
- Loose or missing mortar in block or stone walls
- Erosion of soil at the top or sides of the wall
If your wall is over 1.5 metres high, it likely required a building consent under the NZ Building Code, and the structure may have specific maintenance requirements noted in your consent documentation — worth checking.
Vegetation Management
Plants growing in or immediately behind a retaining wall can cause problems over time. Tree roots in particular can work into joints and drainage layers, displacing material and blocking drainage.
- Remove any self-seeded trees or large shrubs growing directly against or through the wall.
- Keep ground cover plants trimmed so you can still see the wall face clearly.
- Avoid planting large trees close to the wall — check with your retaining wall builder or a landscape professional for appropriate planting distances.
- Moss and lichen on the wall face are generally cosmetic but can hide cracks; clean them off periodically with a stiff brush or appropriate outdoor cleaner.
Timber Wall Specific Care
Timber retaining walls — whether railway sleepers, treated pine, or hardwood — have a finite lifespan. Even H5-treated timber (rated for ground contact) will eventually decay.
- Inspect the base of timber posts and planks annually for softness or discolouration.
- Ensure soil is not piled higher than the wall was designed for, as this accelerates decay at the soil line.
- Ask your builder what treatment level was used; this will give you an indication of expected lifespan.
Concrete and Block Wall Care
- Re-point any mortar joints that have cracked or fallen out, using a suitable exterior mortar mix available from Mitre 10 or Bunnings.
- Seal exposed concrete if recommended by the original builder, particularly in coastal areas where salt spray accelerates deterioration.
- Monitor any control joints (deliberate gaps) to ensure they remain clear and functional.
Keeping Records
Keep a simple maintenance log — even just photos taken from the same spot each year. This makes it much easier to spot gradual movement or deterioration that might not be obvious in a single inspection.
When to Call a Professional
Call a qualified retaining wall builder or structural engineer if you notice:
- Any leaning, bulging, or outward movement of the wall
- Horizontal cracking, especially mid-wall
- Sudden changes after a storm or earthquake
- Weep holes that remain dry even after prolonged heavy rain (may indicate drainage has failed internally)
- Significant timber rot affecting structural posts
- Uncertainty about whether your wall is safe
For walls over 1.5 metres, or walls retaining slopes above buildings or driveways, professional assessment is especially important — the consequences of failure are more serious. You can find qualified retaining wall builders in your area on tradedirectory.co.nz.
If your wall was built under a building consent, your local council may also have inspection records or as-built drawings that can help a professional assess the structure.
Licensed Building Practitioner (LBP)
