Rendering over a wall that previously had exterior tiles may be achievable as a DIY project for small areas, but note that some aspects of exterior cladding work may constitute restricted building work under the Building Act, requiring a Licensed Building Practitioner (LBP). Check with your local council or MBIE before proceeding, but the preparation work is where most of the effort — and most of the risk of failure — lies. Get the substrate right and your render will bond well and last for years; skip steps and you'll likely see cracking, delamination, or moisture problems down the track.
Understand What You're Working With
Before you pick up a hammer, identify your substrate (the wall material behind the tiles). Common exterior substrates in NZ include:
- Fibre cement sheet (e.g. James Hardie products)
- Concrete block or brick
- Lightweight concrete or AAC block
- Timber-framed walls with a building wrap and mesh
The substrate dictates which render system you use, how you prepare the surface, and whether a building consent is required. If you're unsure what's behind your tiles, consult a qualified renderer or builder before proceeding. You can find experienced local renderers on tradedirectory.co.nz.
Check for Building Consent Requirements
In most cases, removing tiles and re-rendering an existing exterior wall falls under Schedule 1 exemptions to the NZ Building Act — meaning no building consent is required, provided the work is like-for-like and doesn't affect the structural or weathertight performance of the building. However, rules can vary, and you should always confirm with your local council before starting. Check MBIE Building Performance for general guidance on what requires consent.
Step 1 — Remove the Old Tiles Safely
Use a cold chisel and club hammer, or a rotary hammer with a chisel bit, to carefully remove tiles. Work from the top down and keep the chisel angle low to avoid gouging the substrate.
Safety note: Old tile adhesive or grout may contain asbestos if the wall was tiled before the mid-1980s. If you suspect asbestos, stop work immediately and contact a licensed asbestos assessor. WorkSafe NZ has guidance on identifying and managing asbestos safely — do not sand, grind, or break suspect materials.
- Wear safety glasses, gloves, and a dust mask (P2 minimum) throughout removal
- Dispose of tile waste responsibly at a licensed facility
Step 2 — Remove Old Adhesive and Prepare the Surface
Once tiles are off, you'll likely have residual tile adhesive bonded to the substrate. This must be removed or keyed back thoroughly — render will not bond reliably to a smooth, contaminated surface.
- Grind or scrape off adhesive high spots with an angle grinder or scraper
- Check for damage: look for cracked, soft, or delaminating substrate and repair or replace affected sections before rendering
- Wash the wall with a stiff brush and clean water to remove dust, salts, and loose material; allow to dry fully
- If the substrate is very smooth (e.g. dense concrete), apply a bonding agent or scratch coat to improve adhesion — products from Sika or Ardex are well regarded in NZ for this purpose
Step 3 — Check Weathertightness Details
Exterior rendering is part of your home's weathertight envelope. Before applying render, inspect:
- Flashings around windows, doors, and penetrations — ensure they're intact and correctly lapped
- Control joints — plan where expansion/control joints will go to manage cracking (typically every 3–4 m and at changes in substrate)
- Drainage at the base of the wall — render should stop above ground level with a proper drip edge
NZ Building Code Clause E2 (External Moisture) sets the performance requirements for exterior claddings. BRANZ publishes excellent guidance on weathertight detailing for rendered walls.
Step 4 — Apply a Bonding Coat or Scratch Coat
For most substrates, apply a scratch coat (a thin, stiff mix of render scratched with a comb float before it sets) to create a mechanical key for subsequent coats. Allow this to cure for at least 24 hours — longer in cool or humid conditions.
If using a fibre cement substrate such as James Hardie products, follow the manufacturer's specific render system recommendations, as some products require a primer or bonding agent rather than a traditional scratch coat.
Step 5 — Apply the Base Coat
Mix your render to a firm, workable consistency — not too wet, or it will slump and crack as it dries. Apply with a steel trowel or render float to an even thickness, typically 10–15 mm for a base coat on masonry, or as specified by your render system.
- Work in manageable sections to maintain a wet edge
- Avoid rendering in direct hot sun, strong wind, or when rain is forecast — these conditions cause the render to dry too fast and crack
- Scratch the surface lightly before it fully sets if applying a finish coat on top
Step 6 — Apply the Finish Coat
Once the base coat has cured (typically 24–48 hours minimum, depending on conditions), apply your finish coat. Options include:
| Finish Type | Appearance | Notes |
|---|---|---|
| Sand finish | Smooth to fine texture | Trowelled flat, popular for modern homes |
| Texture/roughcast | Coarse, rustic | Good for hiding substrate imperfections |
| Acrylic render | Flexible, coloured | Reduces cracking, often used as a top coat |
For colour, acrylic top coats from brands like Resene or Dulux can be applied over cured render, or you can use a pre-coloured acrylic finish coat.
When to Call a Professional
While an experienced DIYer can tackle small render patches, consider hiring a licensed renderer or plasterer for:
- Large wall areas or full house re-cladding
- Any work involving suspected asbestos
- Weathertight repairs where moisture damage is present
- Fibre cement or proprietary cladding systems with specific warranty requirements
- Any situation where you're unsure about the substrate condition
A qualified tradesperson will also ensure the work meets NZ Building Code requirements. Find local renderers and plasterers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
