Spray Rendering Guide

Whether you are looking to refresh a tired 1930s semi or finish a new build, spray rendering provides a breathable, weather-resistant shield. It is particularly popular for through-colour renders like Monocouche, which eliminate the need for future painting.

What Does the Work Involve?

• Site Preparation: Setting up scaffolding and protecting windows, doors, and pathways with heavy-duty masking tape and plastic sheeting.
• Surface Prep: Removing old loose render, cleaning the substrate, and applying a fungicidal wash if algae is present.
• Beading: Installing stainless steel or PVC corner beads and drip beads to ensure sharp, straight lines and proper water shedding.
• Priming: Applying a "key coat" or primer to ensure the spray render adheres perfectly to the specific wall type (e.g., brick, block, or insulation).
• Machine Application: Spraying the render mix in a consistent layer using a diesel or electric render pump.
• Finishing: Leveling the render with a serrated straight edge (darby) and, once partially set, "scraping" it to achieve the final texture.

Typical Costs

Prices for spray rendering are typically calculated per square metre (m²). These figures include materials, labour, and VAT, though scaffolding is often quoted as a separate additional cost.

The total cost is heavily influenced by the condition of your existing walls. If the old render is "blown" (detached from the brickwork) and needs hacking off, expect to pay significantly more for the extra labour and waste disposal.

How Long Does It Take?

• Small Extension: 2–3 days (1 day prep, 1 day spraying/finishing).
• Average 3-Bed Semi: 4–6 days depending on weather conditions.
• Large Detached House: 7–10 days, accounting for multiple elevations and complex masking.

Pro Tip: Rendering is weather-dependent. It cannot be applied in heavy rain or when temperatures drop below 5°C, as the render will not cure correctly.

DIY or Professional?

Spray rendering is strictly a professional-only job. The equipment required—a specialist render pump—costs thousands of pounds to buy and requires significant skill to operate without causing blockages or uneven finishes.

Furthermore, a "bad" render job is incredibly expensive to fix, often requiring the entire surface to be hacked off. Professionals also understand the "open time" of the product, ensuring the finish is scraped at exactly the right moment to avoid colour patches or cracking.

Choosing the Right Tradesperson

• Experience: Ask to see a portfolio of recent spray-applied projects, specifically using the brand of render you want (e.g., K-Rend, Weber, or Parex).
• Accreditation: Look for manufacturers' "Approved Applicator" status, which often means the work can be backed by a product warranty.
• Equipment: Confirm they own or have a reliable hire source for a diesel or electric spray pump, rather than just hand-applying.

Questions to ask:

• "Will you be using a mesh reinforcement layer to prevent cracking?"
• "How do you handle waste and overspray on the property?"
• "What brand of render do you recommend for my specific wall type?"
• "Is scaffolding included in your quote, or is that a separate contract?"

UK Regulations

• Building Regulations (Part L): In the UK, if you are re-rendering more than 25% of a wall, you may be required to upgrade the thermal insulation of that wall to meet current standards.
• Conservation Areas: If your home is listed or in a conservation area, you may need planning permission to change the exterior finish or colour.
• Warranties: Most reputable installers provide a 10-year insurance-backed guarantee on the workmanship and materials.

Common Problems

• Ghosting: This is when the outline of the bricks or blocks shows through the render, usually caused by applying the render too thinly or without a proper base coat.
• Algae Growth: Common in damp UK climates on north-facing walls; choosing a silicone-based spray render can help repel water and prevent this.
• Cracking: Often caused by structural movement or failing to use alkaline-resistant mesh over "stress points" like the corners of windows and doors.
• Overspray: If a contractor is messy, render spray can drift onto cars, neighbours' houses, or garden furniture; ensure they use adequate masking.

Frequently Asked Questions

Does spray render need to be painted?

No. Most spray renders, such as Monocouche or Silicone thin-coat, are "through-colour," meaning the pigment is mixed throughout the material. This saves you the cost of painting every few years.

Can you spray render over existing old render?

It depends on the condition. If the old render is solid and well-adhered, a professional can often apply a "base and mesh" coat over it before spraying. If it is hollow or cracking, it must be removed first.

What is the difference between Monocouche and Silicone render?

Monocouche is a thick, one-coat cement-based render that is scraped for a stone-like finish. Silicone render is more flexible, thinner, and better at resisting cracks and dirt, but it usually requires a separate base coat.

How do I clean spray render?

Most modern renders can be cleaned with a low-pressure jet wash and a specialist fungicidal wash. Never use high pressure at close range, as this can damage the texture of the render.

Will it hide the unevenness of my walls?

To an extent, yes. Spray rendering is excellent for levelling out minor dips and bumps, but very wonky walls may require a thicker "levelling coat" before the final spray finish is applied.