Rendering an external wall gives a fresh, clean finish to tired brickwork or blockwork, provides an extra layer of weather protection, and can dramatically improve your home’s kerb appeal. It’s a physically demanding job — you’re working overhead with heavy material — but the process itself is straightforward. If you can plaster a small area, you can render a wall.
Types of Render
| Type | Mix | Cost per m² | Durability | DIY Suitable? |
|---|---|---|---|---|
| Sand and cement | Cement, plastering sand, lime, water | £5–£10 | Good (20–30 years) | Yes — this guide |
| Monocouche (one-coat) | Pre-mixed bagged render | £10–£20 | Very good (30+ years) | Yes, but technique-sensitive |
| Silicone render | Pre-mixed, factory-coloured | £15–£25 | Excellent (30+ years), self-cleaning | Possible but expensive to DIY |
| Lime render | Lime putty, sand | £10–£15 | Good, breathable | Yes — essential for old buildings |
For most DIYers rendering a garden wall, garage, or extension, traditional sand and cement render is the most practical choice — materials are cheap, widely available, and the technique is well-established. For period properties (pre-1920s with solid walls), use lime render instead — cement render on old buildings traps moisture and causes serious damage. The Historic England guide explains why lime is essential for older buildings.
What You’ll Need
Materials
- Plastering sand (sharp sand, not building sand)
- Cement (OPC)
- Hydrated lime (improves workability and reduces cracking)
- Clean water
- PVA bonding agent (for non-porous surfaces) or SBR primer
- Render beads (corner beads and stop beads for clean edges)
- Stainless steel render mesh (if rendering over painted surfaces or mixed substrates)
Tools
- Plasterer’s trowel (280mm or larger)
- Hawk (for holding render)
- Darby or feather edge (for ruling off)
- Bucket trowel (for mixing and loading)
- Spirit level (1200mm+)
- Sponge float (for sponge finish)
- Scratch comb (for keying the scratch coat)
- Cement mixer or large mixing tub
- Scaffolding or tower scaffold (for anything above reach height)
Mix Ratios
| Coat | Cement | Lime | Sand | Thickness | Purpose |
|---|---|---|---|---|---|
| Scratch coat (first coat) | 1 | 0.5 | 4 | 10–12mm | Keys to the wall, provides flat base |
| Top coat (finish coat) | 1 | 1 | 6 | 6–8mm | Smooth finish coat — weaker mix to reduce cracking |
The top coat should always be weaker than the scratch coat. A strong top coat over a weaker base cracks. The lime in both coats improves workability, flexibility, and reduces the risk of shrinkage cracks.
Step-by-Step Rendering
Step 1: Prepare the Wall
- Remove any loose material, old render, flaking paint, or vegetation
- Rake out any open joints to about 10mm depth — this gives the render a mechanical key
- Brush the wall clean of dust
- Wet the wall thoroughly — a dry, porous wall sucks the moisture from the render before it can cure properly, causing it to crack and debond. Spray with a hose until the water stops being absorbed immediately
- For smooth or non-porous surfaces (engineering brick, painted block), apply PVA bonding agent or SBR primer. For seriously non-porous surfaces, fix stainless steel render mesh first
Step 2: Fix Render Beads
Render beads provide straight, clean edges at corners and stopping points. Fix them with dabs of render mix — check plumb with a spirit level and ensure they’re all at the same projection from the wall. External corner beads protect the render from chipping at corners.
Step 3: Apply the Scratch Coat
- Mix the scratch coat to a stiff but workable consistency — it should hold on the trowel without sliding off
- Load the hawk and apply render to the wall with firm upward strokes of the trowel, pressing hard to ensure a good bond
- Build up to 10–12mm thickness
- Rule off with a darby or straight edge — work upward from the bottom, resting the straight edge on the render beads and drawing it upward in a sawing motion. This cuts the render to a flat plane
- Fill any hollows, rule off again until flat
- While still wet, scratch the surface with a scratch comb (horizontal lines about 3mm deep). This provides a key for the top coat
- Allow to cure for at least 24 hours (ideally 3–5 days). Keep it damp by spraying with water if the weather is hot and dry — too-fast drying causes cracks
Step 4: Apply the Top Coat
- Dampen the scratch coat with water before applying the top coat
- Mix the top coat to a slightly creamier consistency than the scratch coat
- Apply at 6–8mm thickness and rule off as before
- Wait until the top coat has firmed up slightly (usually 2–4 hours depending on weather)
- Finish the surface using your chosen method (see below)
Finish Options
- Sponge finish — dampen a sponge float and work it in circular motions across the surface. Creates a slightly textured, uniform finish. The most common domestic finish
- Scraped finish — once the render has set firm, scrape the surface with the edge of a trowel or a purpose-made scraper. Reveals the aggregate and creates a rustic texture
- Smooth (float) finish — work the surface with a steel trowel for a smooth finish. Requires good trowelling skills — any imperfection shows. Prone to crazing (fine surface cracks)
- Roughcast/pebbledash — throw small pebbles at the wet top coat. Distinctive, very durable, hides imperfections. Our plastering guide covers interior finishing in detail
Common Mistakes
- Not wetting the wall — suction from dry masonry sucks moisture from the render, causing cracking and poor adhesion
- Top coat stronger than scratch coat — causes cracking. Always use a weaker mix for the top coat
- Rendering too thick in one coat — thick render slumps off the wall. Two thinner coats are always better than one thick one
- Rendering in direct sun or wind — causes rapid drying and cracking. Work in shade where possible, or dampen the surface and protect with sheeting
- Cement render on old buildings — traps moisture behind the render, causing damp and structural damage. Use lime render on any building with solid (non-cavity) walls
