Surface finishing for bonding preparation

A bond that looked right on the line can still fail in service if the surface underneath was not properly prepared.

Wet blasting removes the resinous or oxidised surface layer cleanly and consistently, as well as creating a highly reactive surface and profile to which adhesives and coatings can grip. The controlled slurry cushions the abrasive at the point of impact, which means the surface is keyed without being torn - especially important when bonding composites as incorrect surface preparation will damage fibres and consequently weaken the structure. The result is repeatable across an entire batch, not dependent on operator pressure or dry conditions.

Glue being applied to a surface in an industrial process
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How wet blasting surface finishing for bonding works in practice

The slurry carries abrasive particles to the surface in a column of water, which simultaneously cleans and profiles in a single cycle. Water dampens the impact energy, preventing the micro-fractures and embedded contamination that undermine bond strength. Pressure, abrasive grade, and gun angle can each be adjusted independently, giving you precise control over the surface profile you achieve.

Typical setup: surface finishing for bonding preparation

  • Abrasive: Coarse aluminium oxide, 46 to 120 mesh. Note: composites generally require 120 mesh.
  • Pressure: 3 to 5 bar (44 to 73 psi)
  • Guns: Component dependent, manual or automatic
  • Minimum recommended control: Basic process control sufficient for entry-level machines; continuous automatic machines recommended for high-volume or tight-tolerance work
  • Variables: Harder materials require higher pressure and coarser abrasive. In automatic processes, gun positioning is adjusted to ensure full surface coverage on complex geometry.

How Vapormatt controls the wet blasting process

Bonding preparation capability: what wet blasting achieves

The parameters below are indicative and confirmed for the component types listed. Results for other geometries and materials may vary.

Component typeTypical size or weightProcess modeAchievable outcomeMinimum control
Aluminium rod (wire)Ø10 mmAutomatic3.5 to 7 µm Ra; good bond strengthContinuous automatic machine (Profelis)
Bonded studs and standoffsØ8 to 50 mm x 5 to 50 mm tallAutomatic3.2 to 6.3 µm RaBasic manual machine
Composite panels300 x 300 mmManualResinous surface layer fully removed; homogenous finish passing water break testBasic manual machine

In Vapormatt sample processing trials, composite panels for G1c fracture testing were processed on a Cougar machine using APA180/220 blast media at 2.5 to 4.0 bar. All panels achieved a homogenous finish that passed water break tests, with the resinous layer fully removed and samples confirmed ready for structural bond strength testing.

Bonding preparation requirements also arise across aerospace structural assemblies and composite structures, where surface consistency is directly linked to joint integrity. For applications in those sectors, see how wet blasting is used in aerospace MRO operations and across composites manufacture.

Surface angle diagram

Creation of a highly reactive surface

Wet blasting creates a highly reactive surface - a surface with a particularly high surface energy. This can be defined with a 'contact angle' as shown in the diagram opposite.

The contact angle is directly related to the difference between the surface activity of the solid, and the surface tension of the liquid. A high surface reactivity gives a low contact angle, helping paints and coatings to spread out easily across the surface instead of beading.

How is the measurement made? A Goniometer is used to measure the contact angle and determine how wettable the surface is.

'Our Vapormate has without doubt stood the test of time and saves us a lot of man hours. It is also very consistent and reliable'

Josh Rowland - Carbon Art 45

Vapormatt's wet blasting machine, installed at the National Composites Centre in Bristol, is transforming composite bonding performance by delivering clean, precision-abraded surfaces on materials like carbon fibre and GRP - without causing fibre damage.

National Composites Centre - Bristol, UK
Vapormatt Sabre automatic wet blasting machine

The right machine for your bonding preparation application

Vapormate or Puma handles a wide range of component types at low throughput with entry-level control.

Puma+ suits small parts at medium production volume.

Sabre is configured for medium-sized parts where higher process control is required.

Contact us

Find out what Vapormatt machine is best suited to your bonding preparation

Talk to a wet blasting expert

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FAQs

How consistent is the surface profile across a batch?

In automatic processes, gun positioning is set to ensure full coverage, and pressure is held within the specified range throughout the run. Batch-to-batch variation is controlled by the machine parameters, not by the operator. For critical applications, basic process logging is sufficient to demonstrate consistency.

Will wet blasting damage composite fibre structure?

At correctly set pressures, no. In Vapormatt sample processing trials on composite panels, the working range was established at 2.5 to 4.0 bar using APA180/220 media. Fibre damage was observed only when pressure exceeded 4.5 bar, which sits outside the recommended range for composite substrates.

What surface roughness can I expect for metallic components?

For aluminium and steel fastener-type components, confirmed results from sample processing trials show Ra values in the range of 3.2 to 7 µm, depending on the abrasive grade and pressure applied.

How do I verify that the surface is ready for bonding before I apply adhesive?

A water break test is the standard in-process check. A correctly prepared surface holds a continuous water film without beading. This test takes under a minute and requires no specialist equipment. For more accuracy measure the contact angle via a Gonometer.

Can wet blasting handle both metal and composite components on the same machine?

Yes. The recipe is adjusted by changing abrasive grade and pressure. Metal and composite components require different parameter sets, but the same machine can run both with a recipe change between batches.