1. Confirm surface bonding is suitable for your application

Before selecting an adhesive, consider whether surface bonding is the right installation method for your application, production workflows and service environments.

General suitability

Surface-bonded bigHead fasteners are typically appropriate when:

• Drilling through the substrate is undesirable or impossible.
• The substrate has sufficient surface integrity (not friable, powdery, or oil rich) to support the expected loading.
• Production and service environments are compatible with polymeric adhesives.

Surface bonding installation may be unsuitable if:

• The fastening must endure sustained high axial loads.
• The substrate is significantly more flexible than the fastener.
• Adhesive bonding workflows conflict with production processes.
• Long-term exposure to high temperature, aggressive chemicals, or UV is unavoidable.

If adhesive bonding is unsuitable, consider an embedded bigHead installation instead.

Load case sensitivity

Early understanding of the expected load cases will help you select the correct adhesive.

Adhesive bonded bigHead fasteners respond differently depending on how they are loaded:

• Shear loads distribute stresses across the bond area, rather than perpendicularly (flatwise). This is generally the most efficient way for bonded fasteners to carry load.
• Axial pull-off loads are common and valid – but highly sensitive to surface prep, adhesive choice, and curing conditions.
• Peel loads depend on the Head type, substrate stiffness, adhesive toughness, and local geometry.

Use pull-off performance as an indicator of bond quality and process robustness, not as a sole suitability criteria for bonding.

Consider how service loads are applied and distributed in service conditions. To manage high axial loads, combine:

• Correct bigHead product selection
• Appropriate adhesive
• Robust surface preparation

For sustained high axial loads, seek specialist advice from your adhesive supplier. Always validate your selection through application testing.

We can help you select the correct Head type for your adhesive bonding application – get in touch.

For more information on how to assess performance under different loading conditions, see our guide to evaluating fastener installation strength.

2. Understand the substrate surface

Adhesive performance depends on the nature of the surface you are bonding to, not just the structural material composition.

Adhesive manufacturers provide material compatibility information. Treat this as a starting point, not a final answer.

You may see these polymeric material classifications used to indicate generic adhesive suitability:

• Thermoset composites (GRP, CFRP – epoxy, polyester or vinyl-ester)
• Thermoplastics (ABS, PA, PC, PE, PP)
• Filled or reinforced polymers (PUR, PA66 30% CF)

However, it’s important to consider the surface condition, not just the polymer or matrix-polymer type.

Check these surface-related factors:

• Surface energy: PE and PP have very low surface energy.
  For adhesives marketed as ‘suitable for bonding low surface energy materials’, verify that this also delivers adequate mechanical performance for the expected fastening loads.
• Material composition at the bondline: If bonding to coatings, surfacing films or gel coats, the adhesive must be compatible with those layers, not the underlying material.
  You may need to test whether the layers are able to sustain fastening loads without detaching from the structural material.
• Surface topography at the bondline: Peel plies create distinct surface topographies that influence fastener bonding performance.
  If bonding to peel-ply textures, don’t rely on data based on smooth surfaces of the same material. Verify adhesive performance on your actual surface finish.
• Moisture, oils or release agents: Adhesives vary in their ability to disperse moisture and oils, and in their sensitivity to release agents.
  Always check adhesive sensitivity and the practicability of any prescribed surface preparation.

These factors don’t prevent successful bonding, but they do influence adhesive choice, surface preparation, and the need for testing.

3. Define what the adhesive must do

Adhesives for surface-bonded bigHead fasteners typically perform multiple roles. Some adhesives perform one role very well, with a trade-off against others.

Assess which of these roles matter most for performance in your application.

Load transfer

The adhesive carries any axial, shear, and rotational load from the fastener into the substrate. These loads can occur both during assembly fastening and during service.

Be aware of loads created during assembly operations, which can include:

• Axial loads created by operatives using the fastening to ‘pull’ assembly components into their final position.
• Rotational forces created during torque-tightening of the fastening.

Adhesives may respond differently to these load-cases than in a standard shear or peel test.

Gap filling

The adhesive must accommodate any surface waviness or flatness variation across the bondline.

Some adhesives have bondline thickness limitations, which limits the amount of gap filling they can support.

Vibration damping

The correct adhesive can mitigate the stress concentrations transmitted into substrates by repeated cyclic loading of the fastener.

Their ability to do this depends on the formulation and cured physical properties.

Environmental sealing

Moisture ingress at the bondline can become trapped and cause corrosion on the fastener.

If your bonded fastener will be exposed to high humidity or routinely immersed in water, assess the adhesive’s resistance to moisture wicking.

4. Choose an adhesive family

Three chemistry types – or families – are relevant for most applications with bigHead fasteners:

• Epoxy
• MMA (methyl methacrylate)
• Polyurethane

Hybrids exist that combine benefits of different types. But they generally align with one of these three families in terms of suitability.

Use the lists of pros and cons below to spot any strong fit or misalignment with your application.

Treat this as quick guidance and not an exhaustive list. There are options for mitigating limitations, but there are too many to include here!

Epoxy adhesives

What they do well:

• High stiffness and strength
• Jigged/fixtured bonding
• Bonding to advanced composites

Known limitations:

• Lower elongation (typically ~5%)
• Brittle response to peel or impact loads
• Longer cure times unless heat-accelerated

MMA (methyl methacrylate) adhesives

What they do well:

• Multi-material, mixed substrate bonding
• Peel and impact resistance
• Faster fixture times

Known limitations:

• High elongation (>30%) and creep-failure under sustained high loads
• Strong odours and workplace fume restrictions
• Print-through on thin substrates

Polyurethane adhesives

What they do well:

• Highly flexible bonding that withstands dynamic load cycles
• Tolerate differences in thermal expansion across the bondline

Known limitations:

• Lower cohesive strength
• Creep under sustained load

If you’re unsure which family would work best, move on to step 5.

5. Match adhesives to real-world needs

Before engaging with specialists – or comparing adhesive products yourself – it’s helpful to map out and prioritise what you need from the adhesive. This information will help your adhesive supplier to recommend the most suitable product.

Consider the practical requirements of your installation and service environment. How do you need the adhesive to behave during production, fastener installation, and in-service loading?

Below are common real-word considerations for bigHead fastener bonding. Not all will apply to every application, but identifying the ones that matter in yours will help you make a reliable selection.

Flexibility or stiffness (not strength)

Rather than asking “how strong is the adhesive?”, consider how the adhesive bond will be loaded. Ask:

• Will the adhesive bond see static or cyclic loads?
• Is in-service failure more likely to occur through shear or axial overload?
• Is the substrate stiff enough to support a rigid adhesive?

A stiff adhesive on a flexible substrate (or vice‑versa) will change how loads are transferred into the structure, so the balance between stiffness and flexibility often matters more than peak strength.

Thixotropy and handling

For manual bonding (without fixtures to control position), choose a highly thixotropic adhesive that does not sag, slump or run after the bigHead is in place.

Adhesive handling behaviour is particularly important when bonding on slanted, vertical or overhead surfaces.

The ideal adhesive for bigHead fastener bonding:

• Flows like a liquid under the bigHead while pressing it into place.
• Quickly recovers to a thickened state once the fastener is in place.
• Holds the fastener securely until fixture strength develops.

Bondline thickness control

Some adhesives require a minimum or maximum bondline thickness to achieve consistent cure and mechanical performance. Manual placement can make thickness control difficult.

Adhesives containing beads or microspheres help ensure a uniform bondline across the fastener surfaces.

You can add beads or spheres yourself, but it’s usually more convenient to ask your adhesive supplier for products preformulated with bondline control technology.

Working, fixture and cure time

Adhesive cure can be split into three time periods, beginning when the adhesive is mixed and/or dispensed:

• Working time – the time available to apply the adhesive and position the fastener. This limits how many fasteners can be bonded in one operation, and how quickly they must be positioned after adhesive application.
• Fixture time – the point at which the bonded fastener reaches handling strength. This defines when bonded parts can be handled without risk of accidental detachment.
• Cure time – the point at which full mechanical performance is achieved. This defines the earliest point at which service or assembly loads should be applied to the bonded fastener.

Times vary between adhesive systems and are influenced by ambient conditions. Some adhesives gradually cure and strengthen, while others offer rapid ‘snap‑cure’ behaviour.

If you need a faster fixture time or cure time, you may be able to accelerate curing (for example, by applying heat). This depends on the adhesive system and your production constraints.

If cure acceleration is not feasible, ask your adhesive supplier about products with fast fixture or snap‑cure behaviour.

As a guide:

• Select a working time that allows for adhesive application and fastener placement.
• Confirm the adhesive can hold the bigHead in position until fixture strength develops.
• Ensure fixture and cure times align with your production and assembly throughput expectations.

Local availability

Adhesive availability can vary by region. When choosing an adhesive, make sure it’s readily available in all eventual production locations.

Familiarity

If you already use adhesives for composite or multi‑material bonding, you probably have an adhesive and supplier that meets your needs.

If you plan to use the same adhesive for bigHead fastener bonding, evaluate its performance in this specific application first, as performance cannot be assumed from other use cases.

6. Understand the impact of surface preparation

Surface preparation matters more than adhesive choice. It plays a vital role in adhesive bonding, and often delivers greater performance gains than any change of adhesive.

Most surface-bonded failures result from poor surface preparation. In cases of unexpected sub-optimal mechanical performance or durability, review the surface preparation before seeking an alternative adhesive.

For bigHead fastener bonding, consider the preparation of both the substrate and the fastener.

Substrate preparation

Four key steps for preparing polymer-composite surfaces:

1. Degrease (remove mould release, oils)
2. Abrade (create mechanical key)
3. Clean again
4. Apply primer (if required)

For more detail on the methods involved with each step, seek advice from your adhesive supplier.

For bonding bigHead fasteners onto a gelcoat:

The same steps apply, but you may need to use specific cleaning agents and abrasive materials to avoid compromising the gelcoat integrity. Seek advice from your composite materials supplier if needed.

For thermoplastic materials:

Thermoplastic materials often require specialist surface treatments before bonding. Your adhesive supplier should advise on techniques for your polymer and adhesive combination.

bigHead fastener preparation

Clean the bigHead fastener with a suitable solvent (for example, an isopropyl alcohol wipe) before bonding.

Do not abrade the bigHead fastener. Abrasion can remove protective finishes and create micro-pathways for moisture ingress, reducing corrosion resistance.

If you experience bonding issues even after careful cleaning, the adhesive may be incompatible with the fastener material. For example, some self-priming adhesives can etch the organic topcoat on zinc-plated (BZP) parts, exposing the zinc and inhibiting adhesive cure.

If this occurs, revisit your adhesive selection rather than abrading the fastener back to bare metal.

7. Evaluate special cases

Sandwich constructions and metallic substrates introduce extra considerations that influence adhesive selection for bigHead fastener bonding.

Sandwich constructions

The adhesive typically bonds to the skin material, not the core. As a result, the mechanical performance of the fastener is governed by skin composition, local stiffness and local thickness.

Check that the entire sandwich structure can sustain expected fastening loads without risking skin disbond.

On thin sandwich skins, avoid overly stiff adhesives, which can create local stress concentrations and increase the risk of disbonding.

Metallic substrates

Bonding to metals is well understood, but surface finishes and thermal behaviour can influence adhesive performance in bigHead applications.

• Different metals and finishes (e.g. aluminium, steel, powder coating, galvanising) require different bonding approaches.
• bigHead fasteners themselves vary by finish. For example, bright zinc-plated (BZP) parts have an organic topcoat, so an adhesive that bonds well to galvanised steel may not behave the same on a BZP fastener.
• Aluminium can act as a heat sink during cure. Adhesives that rely on exothermic reactions may struggle to reach full cure if the substrate draws heat away from the bondline.

For metallic substrates, evaluate adhesive suitability under the ambient conditions in which bonding will occur. Ensure compatibility with both the substrate finish and the fastener finish.

8. Test and validate your selection

Always validate your adhesive selection. Test with application-representative substrates and bonding process parameters. Don’t rely on data obtained in standardised laboratory conditions.

Adhesive bonding performance is sensitive to:

• Surface condition
• Cure process
• Temperature and ageing

When surface-bonded fastener performance is critical, it’s vital to evaluate mechanical performance. At a minimum, we recommend:

• Axial testing
• Shear testing
• Environmental conditioning (where relevant)

For more information, see our guide to evaluating mechanical performance of surface-bonded bigHead fasteners (coming soon), or get in touch.