Taking the pressure off: how to glue non-porous surface materials
In manufacturing, the bonding process has a few variables that affect success. When it comes to gluing non-porous materials, such as aluminium, brass and copper, pressure becomes the critical variable. Non-porous surfaces don’t absorb glue, so too much clamping pressure can displace glue from the bond line, leaving insufficient glue to form a durable, high-integrity bond. On the production line, a failed bond can halt operations, trigger rework, and lead to scrapped components. Failure post-assembly or in the field can have wider consequences.
In this blog we’ll explore why reducing pressure is key, and how to get consistent, high-quality results when working with non-porous materials.Â
The challenges of bonding non-porous surfaces
It’s natural to assume that the harder two surfaces are clamped together, the better the bond, but this approach is counterproductive for non-porous materials. When gluing a non-porous surface material, such as metal or ‘plastic’, to porous substrates like MDF, chipboard or plywood, excessive pressure can displace adhesive, leaving insufficient bonding material behind. Applying the right amount of controlled, uniform pressure is essential to maintaining optimal adhesive thickness when working with non-porous surfaces.
The signs of too much pressure
Obvious signs of too much pressure being applied are glue oozing out of the sides and immediate bond failure – but not all issues are so easy to spot. In some cases, a product may appear to have bonded at glue stage, only to fail later during CNC machining, handling or end-use. These delayed failures can disrupt downstream processes, lead to costly rework, or cause reputational damage. Furthermore, glue displacement isn’t always obvious – adhesive can soak into open grain at the edges of a porous substrate, masking the fact that the glue didn’t stay where it was needed to provide a reliable bond.
How much pressure is too much?
To put it simply, the pressure typically needs to be reduced much more than most operators imagine. While traditional wood bonding may call for clamping pressures of 100-120 bar, non-porous surfaces require a significant reduction, with optimal results often achieved at just 20-40 bar or less. The objective is to apply just enough pressure to bring the surfaces into uniform contact without displacing any adhesive. As always, material-specific testing is essential to fine-tune the process. Proper surface preparation can also further enhance bond performance and consistency.
Proper material preparation
Successful bonding, especially when using non-porous materials, can be significantly enhanced by thorough surface preparation.
·   Dust and machine residue, including any surface treatment, must be removed as these contaminants can compromise adhesion integrity.
·   Mechanical keying, such as abrasion or scoring, can be used to create texture and increase glue retention for better adhesion.
·   In some cases, acid-etch formulations can be used to chemically activate a metal surface, priming it for better bonding.
·     Both surfaces should be flat with pressure applied evenly across the bond line to ensure uniform contact.
When these preparation steps are executed correctly and combined with controlled pressure, they provide the best conditions for forming a durable bond.
Adhesive types used for bonding non-porous surfaces
Selecting the right glue for a non-porous facing is critical, as different formulations offer distinct characteristics and application methods:
· MS polymers require oxygen to cure and are typically applied in bead patterns to retain air within the bond layer. Pressure control is essential to avoid squeezing out the oxygen.
· Polyurethane (PU) glues vary in performance, with foaming PUs performing better than non-foaming ones on non-porous materials, as the foaming effect helps to prevent glue migration.
· Epoxy resins undergo an exothermic reaction during curing, which can cause the glue to thin. Under excess pressure, this thinner glue squeezes out more easily, compromising adhesion.
· Hotmelt PUR adhesives offer a fast curing, clean-edge solution with thin application, making them ideal for precision work where speed and neatness are priorities.
Understanding the differences between adhesives can help you tailor your bonding process to individual materials and application methods, particularly when working with tricky non-porous surfaces. Above all, the key factor is recognising that pressure is the strategic variable and will normally need to be drastically reduced.
If you’re experiencing issues with bonding non-porous surfaces, we can help.
Contact one of our experts today – we’ll be happy to share our expertise.
