Crumbling mortar joints between garden pavers are a very common issue in New Zealand, where freeze-thaw cycles in cooler regions, heavy rainfall, and UV exposure all take their toll over time. The good news is that repointing — the process of removing old, deteriorated mortar and replacing it with fresh mix — is a manageable DIY job for most homeowners, provided the pavers themselves are still sound and well-bedded.
What Causes Mortar Joints to Crumble?
Before you start repairs, it helps to understand why the mortar failed in the first place:
- Age and weathering – Mortar naturally degrades over many years, especially in exposed outdoor settings.
- Poor original mix – Too much sand, too little cement, or using the wrong type of mortar leads to weak joints.
- Water ingress – Water sitting in joints, particularly in shaded or low-lying areas, accelerates breakdown.
- Ground movement – Slight settling or heave (common on clay soils) can crack and dislodge mortar.
- Tree roots – Roots growing beneath or between pavers can push joints apart.
If you notice widespread cracking, sunken pavers, or significant ground movement, it may point to a deeper drainage or subbase issue worth investigating before you repoint.
Tools and Materials You'll Need
- Cold chisel and club hammer (or an angle grinder with a mortar-raking disc)
- Stiff brush and vacuum or blower
- Pointing trowel or margin trowel
- Bucket and mixing paddle (or a small drill attachment)
- Safety glasses and gloves
- Bagged mortar mix or separate cement and sand
- Water
For most garden paver repointing, a 3:1 sand-to-cement ratio (three parts coarse sand to one part Portland cement) is a standard starting point. Pre-mixed mortar bags are available from Bunnings or Mitre 10 and take the guesswork out of proportions. For areas with heavy foot traffic or vehicle access, a slightly richer mix (closer to 2.5:1) gives extra strength.
Note: Some modern paving systems use polymeric sand or flexible jointing compounds rather than rigid mortar. Check what was originally used — if your pavers were installed with a flexible system, repointing with rigid cement mortar may cause further cracking.
Step-by-Step: How to Repoint Paver Joints
1. Remove the Old Mortar
Using a cold chisel and club hammer, carefully rake out the crumbling mortar to a depth of at least 15–20 mm. Work along the joint without striking the paver edges too hard. An angle grinder with a mortar-raking disc speeds this up considerably but requires care — always wear safety glasses and a dust mask, as silica dust from mortar is a health hazard. Check WorkSafe NZ guidance on working safely with silica-containing materials.
2. Clean the Joints
Brush out all loose debris, dust, and old mortar fragments. A vacuum or leaf blower helps get the joints fully clear. Lightly dampen the joints with water before applying new mortar — this stops the dry substrate from drawing moisture out of the mix too quickly, which weakens the bond.
3. Mix Your Mortar
Mix to a firm, damp consistency — it should hold its shape when squeezed but not be sloppy or wet. A wet mix shrinks more as it cures and is more prone to cracking. Mix only as much as you can use in about 30–45 minutes.
4. Apply the Mortar
Pack mortar firmly into the joint using a pointing trowel, working it in layers if the joint is deep. Avoid smearing mortar across the paver face — if you do, wipe it off promptly with a damp sponge before it sets. Finish the joint slightly recessed or flush with the paver surface; a raised joint catches water and wears faster.
5. Cure and Protect
Keep the repointed area lightly misted with water for two to three days, especially in hot or windy weather. Avoid heavy foot traffic for at least 24–48 hours, and keep the area dry from rain for the first few hours if possible.
Choosing the Right Jointing Product
| Situation | Recommended Product |
|---|---|
| Standard garden pavers, foot traffic | 3:1 sand/cement mortar |
| Flexible or movement-prone areas | Polymeric jointing sand |
| Driveways or heavy loads | Richer mortar or specialist paving adhesive |
| Wet/shaded areas prone to moss | Mortar with added admixture or biocide |
For specialist products, Sika and Ardex both offer paving and jointing compounds suited to NZ conditions — check their product guides for the right choice.
Tips for a Long-Lasting Repair
- Address drainage first — if water pools near the pavers, repointing alone won't last. Improve falls or add a channel drain.
- Don't repoint in freezing conditions — mortar won't cure properly below about 5°C, which is relevant in southern NZ and at altitude.
- Seal the pavers after repointing if they're in a high-moisture area — this slows future deterioration.
- Check BRANZ for guidance on paving and outdoor surface best practice.
When to Call a Professional
Repointing a few joints is well within DIY reach, but consider calling a qualified landscaper if:
- Multiple pavers are sunken, rocking, or cracked — the subbase may need to be rebuilt.
- The problem keeps recurring — there may be an underlying drainage or ground movement issue.
- The area is large — professional equipment makes the job faster and neater.
- You're unsure what jointing system was originally used — using the wrong product can make things worse.
A skilled landscaper can also advise whether your paving layout complies with good practice for surface water drainage, which is relevant under the NZ Building Code for areas close to buildings. You can find experienced local landscapers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
