Yes, you can use adhesive mortar to reattach a single fallen garden brick, and for a small, non-structural repair it's often the most practical DIY option. The key is choosing the right product, preparing the surfaces properly, and understanding when a simple fix is enough versus when a professional bricklayer should take a look.
Is Adhesive Mortar the Right Product?
Adhesive mortar (sometimes called construction adhesive or brick adhesive) is a ready-to-use or mix-yourself product designed to bond masonry surfaces together. It differs from traditional sand-and-cement mortar in that it typically contains polymers or other binders that give it stronger initial grab and some flexibility — useful in garden environments where bricks are exposed to NZ's variable weather, frost in colder regions, and ground movement.
For a single fallen garden brick in a non-structural setting — think a garden edging course, a low decorative wall, or a garden step — adhesive mortar is a perfectly reasonable choice. Brands like Sika and Ardex offer masonry adhesive products widely available at Bunnings and Mitre 10. Always read the product datasheet to confirm it's rated for outdoor and below-ground-level use if needed.
If the brick is part of a structural or load-bearing wall, stop here and call a licensed bricklayer — adhesive mortar alone is not a substitute for properly mixed and jointed mortar in structural applications.
Assessing Why the Brick Fell
Before reaching for the adhesive, take a moment to understand why the brick came loose in the first place:
- Failed mortar joint — the surrounding mortar may be old, crumbling, or was never properly mixed.
- Ground movement or subsidence — common in clay-heavy NZ soils, especially after a dry summer followed by wet winter.
- Frost damage — in colder parts of NZ (Central Otago, Canterbury high country), freeze-thaw cycles can crack mortar and dislodge bricks.
- Water ingress — poor drainage behind a garden wall can build up hydrostatic pressure.
If you notice multiple loose bricks, cracking, or the wall leaning, a single-brick fix won't solve the underlying problem. Check with a qualified bricklayer or, for retaining walls above certain heights, consult your local council — retaining walls above certain heights may require a building consent under the NZ Building Code (the threshold depends on height, soil conditions, and proximity to boundaries; check with your local council). MBIE Building Performance has guidance on when consent is needed.
What You'll Need
- Stiff brush or old paintbrush
- Cold chisel and hammer (to remove old mortar)
- Adhesive mortar (outdoor/masonry rated)
- Notched trowel or margin trowel
- Bucket of water and sponge
- Safety glasses and gloves
Step-by-Step: Reattaching the Brick
1. Clean the surfaces
Chip away all loose or crumbling mortar from both the brick and the cavity it came from using a cold chisel and hammer. Brush away all dust and debris. Both surfaces must be clean and free of loose material for the adhesive to bond properly.
2. Dampen the surfaces
Lightly dampen the back of the brick and the bed it sits on with clean water. This prevents the substrate from drawing moisture out of the adhesive too quickly, which can weaken the bond. Don't soak — just a light mist or wipe.
3. Apply the adhesive mortar
Follow the manufacturer's instructions exactly. Generally, you'll apply the adhesive mortar to the back of the brick and/or the bed using a trowel, ensuring full coverage with no voids. Some products are applied with a notched trowel for better contact.
4. Press and align the brick
Firmly press the brick into position, giving it a slight twisting motion to bed it in. Check it's flush and level with the surrounding brickwork. Remove any squeeze-out from the joints with a damp sponge before it sets.
5. Allow to cure
Keep foot traffic and load off the repair for the time specified on the product — typically 24 hours minimum, longer in cold or damp conditions. Avoid working in temperatures below 5°C, as most adhesive mortars won't cure properly in the cold.
Finishing the Joints
Adhesive mortar may not be ideal for pointing (filling the visible mortar joints around the brick). Once the brick is set, you may want to use a matching ready-mix mortar or jointing compound to neatly fill and finish the surrounding joints. Try to match the colour and profile of the existing mortar as closely as possible — this takes a bit of trial and error, especially on older brickwork.
Tips for a Long-Lasting Repair
- Match your mortar strength to the brick. Older, softer bricks need a softer mortar mix — too hard a mortar can cause the brick face to spall.
- Check drainage. Make sure water can drain away from the base of the wall so the repair isn't undermined again.
- Seal if appropriate. In exposed or high-moisture areas, a masonry sealer can help protect the repair. Resene and Wattyl both offer masonry sealers suitable for outdoor use.
- Work in mild conditions. Aim for temperatures between 10°C and 25°C for best results.
When to Call a Professional
Call a qualified bricklayer if:
- More than one or two bricks are loose or the mortar is failing across a wider area.
- The wall shows cracking, bulging, or leaning — these are signs of structural movement.
- The wall is a retaining wall holding back soil — these are subject to NZ Building Code requirements and may need engineering input.
- You're unsure whether the wall needs a building consent — always check with your local council before doing more than minor repairs.
- The brickwork is heritage or decorative and you want to preserve its appearance.
You can find experienced, local bricklayers on tradedirectory.co.nz who can assess the job and give you a proper quote.
Licensed Building Practitioner (LBP)
