A leaking balcony doesn't always mean ripping up tiles and starting from scratch. In many cases, you can inject or apply waterproofing products through existing grout lines, reseal flashings and penetrations, and restore a watertight surface — saving significant time and money. That said, the success of this approach depends on how badly the underlying waterproofing membrane has failed, so an honest assessment first is essential.
Why Balconies Leak in the First Place
Most NZ balconies leak for one or more of these reasons:
- Failed or cracked grout allowing water to penetrate to the substrate
- Deteriorated sealant at junctions — where tiles meet walls, balustrades, or drains
- Cracked or delaminated waterproofing membrane beneath the tiles
- Blocked or poorly detailed drains causing ponding water
- Inadequate falls (slope) so water doesn't drain away properly
- Flashing failures at the balcony-to-wall junction
Under the NZ Building Code, balconies must comply with Clause E2 (External Moisture) and E3 (Internal Moisture). A balcony over a habitable space is a high-risk area, and the waterproofing system must perform accordingly.
Step 1 — Diagnose Before You Act
Before spending money on products, find out where the water is actually getting in.
- Hose test: Wet one section at a time and watch inside or below for where water appears.
- Check grout and sealant: Look for cracked, missing, or discoloured grout. Tap tiles — a hollow sound suggests delamination or water damage beneath.
- Inspect all junctions: Run your finger along sealant at walls, drains, and balustrade posts. If it's hard, cracked, or peeling, it has failed.
- Check the drain: Make sure it's clear and that tiles slope toward it (minimum 1:100 fall is generally recommended).
If tiles are hollow in large areas or the substrate feels soft, the damage underneath may be too extensive for an over-the-top fix — at that point, tile removal is likely unavoidable.
Step 2 — Regrout and Reseal Joints
This is the most common DIY-accessible repair and works well when the membrane itself is still largely intact.
- Remove old grout to a depth of at least 5–6 mm using an oscillating tool or grout rake. Be careful not to crack tiles.
- Clean thoroughly — remove all dust, mould, and old sealant residue.
- Apply new grout using a flexible, waterproof grout suitable for wet areas. Products from Ardex or Mapei are widely used by NZ waterproofing trades.
- Reseal all movement joints — anywhere two surfaces meet (tile-to-wall, tile-to-drain, around posts) must be sealed with a flexible polyurethane or silicone sealant, not rigid grout. Sika makes a range of suitable sealants for exterior wet areas.
- Allow full cure time before exposing to rain — check the manufacturer's datasheet.
Step 3 — Apply a Trafficable Waterproofing Coating Over Tiles
If grout repairs alone aren't enough, you can apply a liquid-applied waterproofing membrane directly over the existing tiled surface. This is sometimes called an over-tile waterproofing system.
- Products such as those in the Ardex or Mapei ranges include trafficable membranes designed to bridge minor cracks and bond to existing tiles.
- The surface must be clean, sound, and free of any loose material.
- Apply in the number of coats specified by the manufacturer — typically two or more.
- Reinforce all junctions and cracks with fibreglass mesh tape embedded in the first coat.
- Once cured, the surface can be left as-is (if the product is UV-stable and trafficable) or re-tiled over the top.
Important: Always read the technical data sheet and confirm the product is rated for exterior, trafficable, and wet-area use. Not all waterproofing membranes are suitable for foot traffic or NZ UV exposure.
Step 4 — Address Flashings and Penetrations
Even a perfect membrane repair will fail if flashings aren't right.
- Wall-to-balcony junction: There should be a continuous upstand of waterproofing membrane running up the wall behind cladding — at least 75 mm above the tile surface is a common minimum. If this has failed, a bead of flexible sealant is a temporary fix, but a proper flashing repair may require a licensed tradesperson.
- Drain collar: The drain flange must be bonded into the waterproofing layer. Apply sealant around the drain collar and ensure it's not cracked.
- Balustrade posts: Each post penetration is a potential leak point. Seal thoroughly with a flexible exterior sealant.
What You Can and Can't Do Yourself
| Task | DIY OK? | Notes |
|---|---|---|
| Regrout tiles | Yes | Use correct wet-area grout |
| Reseal junctions with silicone | Yes | Clean surface thoroughly first |
| Apply over-tile membrane coating | Yes (with care) | Follow manufacturer instructions exactly |
| Repair or install flashings | Sometimes | Complex flashing work may need an LBP |
| Structural repairs to balcony deck | No | Requires Licensed Building Practitioner |
| Plumbing to drain | No | Restricted work — PGDB licensed tradesperson required |
When to Call a Professional
Call a qualified waterproofer or Licensed Building Practitioner if:
- Water is getting into the structure below (ceiling stains, rotting timber, mould inside)
- Large areas of tile are hollow or the substrate feels soft or spongy
- The balcony is over a habitable room and leaks are significant
- You're unsure whether a building consent is required — always check with your local council before undertaking significant waterproofing repairs, as some work may not qualify as a Schedule 1 exemption
- The original waterproofing system has completely failed
A professional waterproofer can also carry out a proper flood test to confirm the repair has worked. You can find qualified local waterproofing tradespeople on tradedirectory.co.nz.
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