Rendering an old, tired brick or concrete block wall is one of the most effective ways to transform your garden. A fresh render coat covers mismatched bricks, repairs eroded mortar lines, and creates a clean, modern backdrop for your plants. It also acts as a protective shield against rainwater and frost damage.
While rendering requires physical effort and patience, it is a highly satisfying project you can attempt yourself. In this step-by-step guide, we outline the tools and materials you need, the correct mixing ratios, the application process, and when to hire a professional plasterer on GetBuilder.
Tools and materials checklist
Before you begin, gather the following tools and materials:
- Materials: Rendering sand (sharp sand or a plastering sand mix), Portland cement, hydrated lime, clean water, and a liquid waterproofer/plasticizer additive.
- Tools: Plastering trowel, hawk, scratcher (or a scrap wood strip with nails), wooden float, sponge float, brick trowel, plastering corner beads, mixing tub (or concrete mixer), stiff brush, and spirit level.
1. Wall preparation: The key to adhesion
Render will not stick to a dusty, crumbling, or dirty wall. Prepare your brickwork with these steps:
- Clean the wall: Use a wire brush and bucket of water to scrub away moss, dirt, and loose paint. If mortar joints are crumbling, rake them out to a depth of 10mm to give the render a physical key to grip.
- Fix suction levels: Extremely dry brickwork will suck water out of your wet render too quickly, causing it to crack and fall off. Spray the wall down with a hose the evening before, and damp it down again right before applying the render. For high-suction bricks, apply a bonding agent (like water-diluted PVA or SBR bonding slurry).
- Install corner beads: Cut and fix metal or plastic render corner beads on any vertical edges using dabs of rapid-set mortar. This ensures your corners are perfectly straight and impact-resistant.
2. Mixing the render: Ratios and additives
For external walls exposed to UK rain and frost, we use a two-coat system. Lime is added to make the mix more workable and flexible, preventing hairline cracks:
- Scratch Coat (First Coat - Strength):
- Ratio: 4 parts sand to 1 part cement to 1 part lime.
- Additive: Include waterproofer/plasticizer in your mixing water according to manufacturer guidelines.
- Float Coat (Second Coat - Finish):
- Ratio: 5 parts sand to 1 part cement to 1 part lime (slightly weaker than the first coat to prevent cracking).
Note: Always mix the sand and cement thoroughly while dry before adding water to prevent lumps.
3. Applying the scratch coat (First Coat)
The scratch coat should be around 8mm to 10mm thick.
- Load the hawk: Use your brick trowel to place a scoop of wet render onto your hawk.
- Apply to the wall: Hold the hawk close to the wall, tilt it slightly, and use your plastering trowel to sweep the render upward onto the brickwork. Maintain a firm, even pressure to push the mix into the joints.
- Flatten the surface: Once the wall section is covered, use a straight edge or float to smooth the render to a consistent depth.
- Create the key: While the render is still soft but starting to set (usually 30-60 mins), run your scratcher gently across the surface in a cross-hatch pattern. These scratches provide a mechanical key for the second coat to bind to. Let the scratch coat cure for 24 hours.
4. Applying the float coat and finishing (Second Coat)
- Dampen the scratch coat: Lightly spray the cured scratch coat with water so it doesn't suck moisture from the new mix.
- Apply the second coat: Trowel on a slightly thinner layer of float coat (approx. 6mm to 8mm thick).
- Float and level: Once the second coat has started to firm up (usually 1-2 hours), rub a wooden or plastic float in circular motions over the render. This compresses the surface and removes any trowel marks.
- Sponge finish: For a smooth plaster finish, finish by gently rubbing a damp sponge float over the surface. This draws out the fine sand particles, leaving a uniform, professional texture. Let it dry completely for 48 hours before painting with exterior masonry paint.
When to hire a professional plasterer
Rendering long or high garden walls requires speed, as the render must be applied and floated before it dries. If render dries unevenly, it will show visible joints and patchiness.
If you prefer a flawless finish or have a large project, GetBuilder can connect you with qualified plasterers in your area:
- Post your plastering job: Outline the size of the wall, current condition, and location for free on GetBuilder.
- Check specialist profiles: Look for local plasterers checked for active insurance and reference portfolios of exterior rendering projects.
- Compare transparent quotes: Receive up to three competitive written estimates from local professionals with zero success fees.
