Common Mistakes to Avoid When Installing Insulation Fixings
Using the wrong anchor length, over-driving fixings, or placing them in the wrong spot can undo all your hard work. This guide walks you through the most common errors and how to get it right first time.
Using the Wrong Anchor Length
This is one of the most common errors on site. The anchor must be long enough to pass through the full thickness of the insulation board and still embed correctly into the base material beneath.
If the anchor is too short, it will not reach the masonry, concrete, or blockwork. The fixing will have little or no grip in the substrate. The board may feel secure at first, but it will not hold under load or over time.
If the anchor is too long, the sleeve can protrude out from the face of the board. This creates a hard point that can crack the render finish or prevent a flat surface on the insulation layer.
If you are fixing through multiple layers such as insulation plus a render base coat or an air gap membrane, include each layer in your total length calculation. A single layer calculation is the most common cause of under-length anchor orders.
Drilling to the Wrong Depth
The drill hole must be deep enough for the anchor to sit correctly. Too shallow and the fixing cannot be driven to the correct position. Too deep and the hole may not grip the anchor expansion zone properly.
A common rule is to drill the hole at least 10mm deeper than the required embedment depth in the substrate. This gives room for drilling dust at the bottom of the hole. Dust left in the hole reduces the grip of the anchor in the base material.
After drilling, remove all drilling dust from the hole before inserting the anchor. Dust acts as a buffer between the anchor and the substrate wall. It reduces pull-out resistance significantly. Use a brush, blow pump, or vacuum attachment to clean the hole before every fixing.
In aerated concrete (aircrete blocks), the drill must be used in rotary mode only. Using hammer action in aerated concrete damages the material around the hole. This reduces the pull-out strength of the anchor and can cause cracking in the block.
In hollow or perforated materials such as cavity brickwork, the hole depth and the anchor type must suit the hollow section. Standard solid-wall anchors will not expand correctly in hollow materials. Check the product specification matches your substrate category.
Many insulation anchors have a minimum embed depth marker moulded into the sleeve. Use this as a visual guide during installation. When the marker is flush with the face of the insulation, the anchor is at the correct depth.
Over-Driving or Under-Driving Fixings
Getting the drive depth right is just as important as getting the anchor length right. Both over-driving and under-driving cause problems.
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Over-driving When a fixing is driven too far, the large head disc cuts into the surface of the insulation board. This compresses the material around the fixing point. It creates a dip or depression in the board face. In rigid boards such as EPS or PIR, this can crack or split the surface. The damaged area then has reduced insulation value at that point, creating a localised weak spot.
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Under-driving When a fixing is not driven fully home, the head disc sits proud of the insulation surface. This means the disc is not making full contact with the board. The clamping effect is reduced. The board is not held flat against the substrate. In an external wall insulation system, a proud fixing head will also create a bump under the render finish.
The head disc should sit flat and flush with the surface of the insulation board. It should not be recessed below the surface, and it should not protrude above it. Drive the fixing until the disc makes contact with the board face and lies flat across the full disc diameter.
For hammer-in anchors, use a clean, flat-faced hammer or rubber mallet. Aim for even strikes. Avoid sharp, angled blows that can tip the anchor and cause an uneven disc contact. For screw-in anchors, use a torque-setting driver if available to prevent over-driving.
Using Too Few Fixings Per Board
Under-fixing is one of the hardest mistakes to spot and one of the most damaging over time. A board fixed with too few anchors may look secure on the day. Over months and years, it can shift, bow, or detach.
The number of fixings needed per square metre depends on several factors. These include the board type, the board weight, the height of the installation on the building, and the wind load for the location. Buildings in exposed locations or above a certain height require more fixings per square metre than sheltered low-rise walls.
| Location on Building | Typical Fixings per m² | Why More May Be Needed |
|---|---|---|
| General field (centre of wall) | 5 to 6 per m² | Standard wind load in sheltered positions |
| Perimeter zones (edges of wall) | 6 to 8 per m² | Higher suction and wind pressure at wall edges |
| Corner zones | 8 or more per m² | Maximum wind load concentration at building corners |
| Above 8m height | Refer to engineer or ETA specification | Increased wind load at height requires engineering assessment |
Always check the fixing density stated in the system specification or the anchor manufacturer's European Technical Assessment (ETA). These documents give the minimum number of fixings per m² for different substrate and exposure categories. Do not estimate from a general rule if a specification exists for the product.
Placing Fixings Too Close to Board Edges
Insulation boards can crack or split if a fixing is placed too close to the edge. The material around the hole is under stress when the anchor expands. Near an edge, there is not enough material on all sides to distribute that stress.
As a general guide, fixings should be placed no closer than 150mm from any board edge. This applies to all four sides of the board, not just the vertical or horizontal edges.
The same principle applies to the corners of each board. Corners are areas of concentration where cracks can start. Place fixings in from the corners, not directly at them.
Do not place fixings directly on the joint line between two boards. Fixings at a joint can cause the adjacent board edge to lift or pull away. Each board should be independently fixed with its own set of anchors. The joint between boards should be handled with adhesive and tight board contact, not with fixings that span across the joint.
For mineral wool boards and softer insulation materials, edge placement is even more important. Softer materials compress under load. A fixing too close to the edge of a mineral wool slab can cause the edge to deform or detach over time.
Ignoring the Substrate Type
Not all insulation anchors work in all base materials. Using an anchor rated for solid concrete in a lightweight blockwork wall is a common mistake. The pull-out performance in soft materials can be much lower than in dense concrete or brick.
Different substrates have different properties. Concrete, dense aggregate block, perforated brick, aerated concrete, and hollow block all require different anchor specifications. The anchor must be selected to suit the substrate it is going into, not just the insulation it is going through.
- In dense concrete and masonry, a standard plastic hammer anchor with an expansion nail performs well.
- In aerated concrete blocks, a longer embedment depth is often required to achieve the same pull-out resistance.
- In hollow or perforated brick, the anchor must be designed to expand inside the hollow section or use a different fixing mechanism.
- In timber frame construction, the anchors and disc type are different from masonry wall anchors.
- In older or unknown substrates, a pull-out test on site is the only reliable way to confirm the fixing performance before committing to a full installation.
If you are unsure about your substrate category, check the product datasheet or ETA document for the anchor you are using. These list the tested substrate types and the corresponding pull-out values. Choosing an anchor without checking substrate compatibility is one of the most avoidable mistakes on any EWI project.
Creating Thermal Bridges Through Fixings
Every metal component that passes through insulation creates a path for heat to travel. This is called a thermal bridge. The more conductive the material, the greater the heat loss at that point.
Metal insulation fixings have a higher thermal conductivity than plastic fixings. In applications where thermal performance is critical, using metal anchors without a thermal break can measurably reduce the energy efficiency of the wall build-up.
Plastic insulation anchors reduce this effect significantly. Polypropylene and polyamide have very low thermal conductivity. They carry very little heat from the warm inner wall to the cold outer surface. This is why plastic fixings with thermal heads are preferred in high-performance insulation systems.
Many insulation anchors available from JALFT use a large-diameter plastic disc head that sits on the face of the insulation. The low thermal conductivity of the disc material reduces heat transfer through the fixing point. When choosing between metal and plastic anchors, consider both the structural load requirement and the thermal performance target for the project.
Skipping Adhesive Alongside Mechanical Fixings
Mechanical fixings and adhesive bonding are designed to work together in most EWI systems. Using only one method without the other is a common shortcut that causes long-term problems.
Adhesive alone may not provide enough security in exposed locations or for heavier board materials. Over time, adhesive can lose bond strength due to moisture cycling and temperature change. Mechanical fixings provide the long-term structural hold that adhesive cannot guarantee on its own.
Mechanical fixings alone may not create full surface contact between the board and the substrate. Without adhesive, air pockets can form behind the board. These air pockets act as a path for moisture ingress and significantly reduce the thermal performance of the insulation system.
Apply adhesive to the back of the board or to the wall surface in the pattern specified for your system. Then fix the board to the wall using the correct number of mechanical anchors. Allow the adhesive to cure for the time specified before applying any render or basecoat layer. Never start drilling for fixings before the adhesive has achieved adequate initial bond strength. Many systems recommend waiting at least 24 hours after adhesive application before drilling.
If you are working on a ductwork or HVAC insulation project using self-adhesive stick pins rather than masonry anchors, the same principle applies in reverse. Stick pins provide the holding force, but the insulation blanket must also be correctly wrapped and overlapped to seal the joints. A fixing cannot compensate for poor joint sealing.
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