The Ultimate Guide to External Wall Insulation and Render Removal

Improving your home’s insulation is one of the best investments you can make—not only to boost energy efficiency but also to eliminate damp and mould issues. In this blog, we take you behind the scenes of a real-life render removal and external wall insulation project. Whether you’re a DIY enthusiast or looking to hire a professional, this step-by-step breakdown offers valuable insights, tools, and tips to get the job done right.

Why External Wall Insulation Matters

External wall insulation (EWI) is a game changer, especially for older homes. Not only does it improve the aesthetic of the property, but it also dramatically boosts thermal performance and tackles issues like moisture ingress and mould.

In this particular project, the client was struggling with severe damp and mould problems. Our mission? To remove the failing render and wrap the property in 100mm EPS (expanded polystyrene) insulation, ultimately creating a warm, watertight, and visually appealing home.

Step 1: Site Preparation and Assessment

Before lifting a single tool, we start by assessing the entire working area:

Checking the condition of existing render: Cracks, crumbling, and visible damage indicated total removal was necessary.
Protecting surrounding features: Windows were shielded using a combination of ply or correx, depending on the roof overhang.
Organizing the workspace: Tools, materials, and protection barriers were prepared for maximum efficiency.

Step 2: Render Removal – More Than Just Hammer Work

Contrary to popular belief, render removal is not just about bashing away with a demolition hammer. Here’s what you really need:

Tools Used:

Three types of hammer drills (small, medium, and large)
Chisel heads: 4-inch heads proved more efficient than 6-inch ones for this brittle render
Brushes and vacuums: Essential for dust control and surface preparation

Key Challenges:

Poor render condition: Although crumbly, it was stubborn and came off in awkward chunks.
Heavy lifting: The hammer drill alone weighed over 7kg—physical strength and technique are crucial.
Battery life: Lightweight drills like the Milwaukee tear through batteries quickly.

Safety Note:

Always wear protective gear—dust masks, gloves, and goggles are essential.

Step 3: Cleaning and Priming the Surface

After render removal:

Brush down the surface: Use stiff-bristled brushes to remove all loose particles.
Optional rinse: Hosing down the wall helps eliminate lingering dust.
Apply primer: We used a universal red primer to ensure proper adhesion of adhesives or render.

Why it matters? Without this step, dust can cause adhesives to detach, ruining the entire insulation process.

Step 4: Installing the Starter Track and Plinth

The starter track is a crucial element that supports the insulation boards and ensures water resistance at the base:

Decorative plinth: Added for enhanced aesthetics and damp-proofing
Waterproof silicone: Used beneath the starter track for additional sealing
Track positioning: Runs consistently around the perimeter at damp-proof course height

Step 5: Cutting EPS Insulation – The Right Way

One standout moment in the project was using a hot knife to cut 100mm EPS insulation. Why?

Benefits of Using a Hot Knife:

Precision: Clean, accurate cuts without the mess of traditional saws
Efficiency: Reduces waste and speeds up the process
Minimal cleanup: Unlike saws, no bits of polystyrene flying everywhere

Pro Tip: If you’re new to cutting insulation, use a guide or wooden block to maintain straight lines.

Step 6: Preparing for Installation

Before mixing adhesive:

Pre-cut all boards: Have multiple pieces ready to go for continuous workflow
Use proper tools: A render pump helps apply adhesive evenly and quickly

Adhesive Application:

Coverage: Aim for about 40% adhesive coverage on the board
Installation: Press each board firmly into place for maximum contact with the wall

Note: While pumps aren’t mandatory, they save time and ensure better material usage.

Final Thoughts and Professional Tips

This project was not just about fixing a cosmetic issue; it was about restoring a home. Through careful render removal, detailed surface preparation, and precise insulation installation, we were able to transform a damp-ridden property into a warm and safe environment.

Key Takeaways:

Proper preparation is non-negotiable
Use the right tools for better results and less fatigue
Don’t skip priming and plinth installation—they’re critical for longevity
Hot knives are your best friend for cutting EPS insulation cleanly