How to Install External Insulation for Walls Yourself

Many homeowners want to install external wall insulation to reduce energy costs and enhance home comfort. However, it can seem daunting without proper guidance and know-how.

This article provides step-by-step instructions for installing external wall insulation. Roll up your sleeves and be ready to make your home more energy-efficient and comfortable.

  1.  Prepare Walls for External Insulation

Carefully inspect all areas of the walls you plan to insulate. Look for any cracks, holes, deterioration, or damage that needs to be repaired first. Even small defects can prevent the insulation from adhering properly.

Check for any protruding surface attachments like nails, hooks, or debris that could affect the flatness of the insulation install. Remove these obstructions.

Once repaired, the existing walls must be thoroughly cleaned to remove any dirt, dust, oils, paints, efflorescence or other contaminants that could inhibit adhesion. Use the necessary degreasers, detergents or chemical cleaners to ensure a clean and dry substrate.

For previously painted surfaces, it’s recommended to remove glossy paint or use a slicker coating to enable sufficient adhesion of the insulation.

  1. Gather Essential Materials and Tools

After preparing the walls, you need to gather the essential material and tools such as: 

Materials:

  • Rigid insulation boards – You’ll need rigid insulation boards made for exterior use, such as expanded polystyrene (EPS) or mineral wool boards. EPS is a popular affordable option that is lightweight yet durable.
  • Adhesive – A cementitious adhesive mortar formulated for bonding insulation to walls is required. Choose one suited for your wall material like brick, concrete, etc.
  • Reinforcing mesh to go over the insulation – Glass fiber mesh provides impact resistance when embedded into the insulation system with a base coat.
  • Base coat – This polymer-modified base coat secures the reinforcing mesh over the insulation boards before the finish coat goes on.
  • Top coat/render for the final weatherproof finish – The final weatherproof top coat can be a polymer render, acrylic finish or other decorative exterior coating of your choice.

You’ll also want these basic tools:

  • Trowels and putty knives
  • Utility knife for cutting boards
  • Drill for mixing coatings
  • Safety gear like gloves, goggles, dust mask

Having all your materials ready makes the DIY project easier. Don’t try to cut corners!

  1. Measure and Cut Insulation Boards

Take precise measurements of the wall surface area you plan to insulate. Break it down into sections and measure the height and width of each section. Having accurate measurements is crucial for cutting the boards to fit properly.

Use a laser measure or roll out a long tape measure to get the dimensions right. Make sure to account for any obstacles like windows, doors, vents etc. that the insulation needs to wrap around.

Once you have all your measurements, transfer them to the insulation boards and use a straight edge to mark your cut lines. A speed square can help ensure nice 90 degree corners.

An insulation utility knife with a sharp blade works best for cutting through the rigid foam boards cleanly. Apply steady, firm pressure and make multiple passes along the cut line if needed.

For curved cuts around windows or other obstacles, score the line first before snapping off the excess. Specialty insulation saws or hot knives can also be used.

Try to minimize the number of joints between boards as much as possible. Staggering the joints in a staggered/brick pattern can enhance the structural integrity of the insulation system.

Take your time measuring and cutting accurately. Precisely fitting the boards together on your walls with no gaps is crucial for optimal insulation performance and durability. Getting this prep step right ensures a smooth installation.

  1. Apply Adhesive and Insulation Boards

After getting the right measurement and cuts, you’re ready to start applying them to the walls using the adhesive mortar.

Mixing the Adhesive

Follow the manufacturer’s instructions for properly mixing the adhesive mortar. You’ll typically need to combine the dry mortar mix with the specified amount of water or polymer additive.

Use a drill fitted with a mixing paddle to thoroughly blend the adhesive until it reaches a smooth, lump-free consistency. Avoid over-mixing which can cause air entrainment.

Let the adhesive slake (rest) for around 5-10 minutes, then give it a brief remixing before use. This allows the adhesive to reach its optimal workability.

Applying Adhesive and Boards

Using a notched trowel, spread the adhesive onto the backside of the insulation board in a thick, enough layer to create good surface coverage when pressed to the wall.

For best adhesion, apply the adhesive in a ribbed pattern rather than a smooth layer. The notches create more bonding surface area.

Firmly press or “studs shoot” the board into position on the wall using a slight twisting motion. This collapses the adhesive ridges and maximizes contact.

Stagger the board joints in a brickwork pattern as you progress across the wall. Use plastic insulation fasteners, nails or screws every 16-24 inches around board edges and centers to temporarily secure boards while the adhesive cures.

Allow a 1/4-1/2 inch gap wherever insulation boards join together to allow for expansion/contraction.

Work in manageable sections and ensure boards are properly aligned and level as you go. Any adhesive that squeezes out can be tooled away for a neat appearance.

  1. Install Reinforcing Mesh and Base Coat

After the insulation boards have firmly adhered to the wall, the next step is embedding the reinforcing mesh into a polymer-modified base coat layer.

Mixing the Base Coat

As with the adhesive, follow the manufacturer’s manual guide precisely for mixing the dry base coat material with the specified amount of water and/or liquid polymer additives.

Use a drill fitted with a mixing paddle and blend thoroughly to a smooth, lump-free consistency. Avoid over-mixing. Let the mix slake for 5-10 minutes, then give it a final mixing before application.

Applying Base Coat and Mesh

Beginning at the bottom, use a trowel to apply the base coat mix directly onto the insulation board surface in a thick, generous coat.

Immediately after applying the base coat, embed the reinforcing mesh into the wet material by layering it onto the surface. Use a trowel to fully encapsulate the mesh, working the base coat through the mesh holes.

On corners and edges, wrap the mesh around the board and ensure it is fully encased in the base coat with no voids or mesh protruding.

Overlap adjoining sections of mesh by 2-4 inches depending on manufacturer guidance. Smooth out any wrinkles in the mesh before the base coat begins to set.

Once the entire area has mesh embedded in the first base layer, apply a second coat to fully cover the mesh so no mesh pattern shows through. Feather out this top layer to achieve a smooth, level surface.

Allow the base coat to fully cure per manufacturer dry times before proceeding. This creates a strong reinforced layer ready for the finish top coat.

  1. Apply Weatherproof Top Coat

Apply Top Finish Coat The top coat provides decoration, texture and crucially, weatherproofing for your exterior insulation system.

There are various options for the finish top coat, including polymer-based renders, 100% acrylic finishes, and other specially formulated weatherproof coatings.

Consider factors like climate, desired aesthetic, and maintenance needs when choosing the top coat. Some are more flexible, better able to bridge hairline cracks, more moisture resistant etc.

An acrylic-based top coat is a durable, breathable and commonly used option. It can provide a smooth, textured or aggregated finished appearance.

Mixing and Applying

As with the other layers, follow manufacturer recommendations for properly mixing the top coat materials to the correct consistency and workability.

Apply the top coat liberally over the cured base coat using a trowel, spray machine, or other recommended method in one or more coats as needed to achieve the desired thickness and texture.

On larger areas, consider installing stop beads to create visual breaks and control where the applicator starts and stops the texture pattern.

When the job is complete and the top coat has fully dried/cured, your exterior wall insulation system is officially installed and weatherproof!

The reinforced insulation along with the protective top coat now provides an exterior thermal blanket for enhanced energy efficiency.

Conclusion

Completing an external wall insulation project yourself is absolutely achievable for the diligent DIYer.  Don’t feel daunted by the number of steps involved. The key is having patience and paying close attention to the manufacturer instructions. 

Don’t try to rush through or take shortcuts. An exterior insulation system done right will improve your home’s comfort and energy performance for decades.

If you need help with your external wall insulation. Feel free to contact us. You deserve to have the best home of your dreams.

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