Rendering a concrete block wall is a satisfying DIY project, but having the right tools makes the difference between a professional-looking finish and a patchy, cracking mess. Below is a comprehensive guide to the tools you'll need, how they're used, and a few important NZ-specific considerations before you start.
Essential Tools for Rendering a Concrete Block Wall
Rendering is typically done in one or two coats — a scratch coat (base coat) and a finish coat. Each stage benefits from specific tools.
Mixing Tools
- Bucket or mixing trough – A sturdy 20–40 litre plastic trough is ideal for mixing render by hand or with a mixer.
- Paddle mixer / drill mixer – Attach a mixing paddle to a heavy-duty drill (at least 850W) to blend render to a smooth, lump-free consistency. This saves significant time and effort compared to hand mixing.
- Measuring bucket – Consistent water-to-mix ratios are critical. Use a marked bucket to measure water accurately every batch.
Application Tools
- Plasterer's hawk – A flat aluminium or plastic board with a handle underneath. You hold the hawk in one hand to carry a working load of render while you apply it with the other.
- Steel trowel (laying-on trowel) – The main tool for pressing render onto the wall. A rectangular stainless-steel trowel (typically 280–330 mm) is standard. Keep it clean and slightly damp to prevent drag.
- Margin trowel – A smaller trowel for scooping render from the bucket onto the hawk, and for working into corners and tight spots.
- Notched trowel – Useful if you're applying a polymer-modified base coat that requires a keyed surface for a second coat to bond to.
Levelling and Screeding Tools
- Aluminium straight edge (screed rail / darby) – A long, straight aluminium bar (1.2–1.8 m) used to rule off and flatten the render between grounds (depth guides). This is essential for achieving a flat, even surface.
- Spirit level – Use a 1.2 m or longer level to set your grounds accurately before you start screeding.
- Feather edge / floating rule – A slightly shorter, lighter version of the straight edge, useful for smaller sections.
Finishing Tools
- Wooden or sponge float – Used after the render has started to firm up (the "green" stage) to compact and texture the surface. A sponge float gives a smoother, finer finish; a wooden float gives a more textured, sand finish.
- Plastic float – A good all-rounder for finishing coats, especially with bagged render mixes.
- Wet brush or spray bottle – Lightly misting the surface during floating helps achieve a consistent finish and prevents the render drying too fast, which can cause cracking — especially important in hot, windy NZ summers.
Preparation and Sundry Tools
- Wire brush / angle grinder with wire cup – Clean loose material, dust, and efflorescence off the block surface before you start. Good surface prep is the single biggest factor in render adhesion.
- PVA bonding agent or block primer – Not a tool, but essential. Products from Ardex, Sika, or Mapei are widely used to prime concrete block and improve adhesion. Apply with a brush or roller.
- Paintbrush (100–150 mm) – For applying bonding agent and for dampening the wall before applying render.
- Masking tape and plastic sheeting – Protect windows, doors, and adjacent surfaces from splatter.
- Render grounds / screeding beads – Metal or timber strips fixed to the wall at the desired render thickness (typically 10–15 mm for a single coat on block) to guide your straight edge.
- Safety glasses and gloves – Render is alkaline and can irritate skin and eyes. Always wear PPE. See WorkSafe NZ for guidance on working safely with cement-based products.
Handy Tool Comparison Table
| Tool | Stage | Why You Need It |
|---|---|---|
| Paddle mixer + drill | Mixing | Consistent, lump-free render |
| Hawk + steel trowel | Application | Carry and press render onto wall |
| Aluminium straight edge | Levelling | Flat, even surface between grounds |
| Sponge / wooden float | Finishing | Texture and compact the surface |
| Wire brush | Prep | Remove dust and loose material |
| Bonding agent + brush | Prep | Improve adhesion to block |
Where to Buy Tools in NZ
Most of these tools are available from Bunnings, Mitre 10, and PlaceMakers. PlaceMakers and trade merchants often stock a wider range of professional plastering tools and bagged render products.
NZ Building Code Considerations
If you're rendering an exterior wall as part of a weathertightness system, be aware that the NZ Building Code Clause E2 (External Moisture) sets performance requirements for cladding systems. Render on concrete block is generally straightforward, but if you're rendering as part of a new cladding system or making significant changes, check with your local council whether a building consent is required. For guidance on consent exemptions under Schedule 1, visit MBIE Building Performance. BRANZ also publishes useful technical guidance on render systems.
When to Call a Professional
Rendering looks simple but takes practice to get right — particularly achieving a flat, crack-free finish over large areas. Consider hiring a qualified renderer if:
- The wall is large (over 20–30 m²) or highly visible
- You need to match existing render texture or colour
- The wall has significant cracks, movement joints, or moisture issues that need diagnosing first
- The render is part of a consented weathertight cladding system
A skilled renderer will have the tools, technique, and product knowledge to get the job done efficiently. You can find qualified local renderers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
