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50 Shades of Glue

Maintenance Engineers often leave a trail of oil and grease around the jobsite or workshop. This can become an issue if they are working with different strength threadlocking adhesives – once the label on the package is soiled, it can be difficult to visually see  the grade reference or part number  on the bottle. However, most adhesive manufacturers operate a colour-coding system for anaerobic threadlockers which is recognised throughout the industry:

PURPLE – Low strength, easy to disassemble
BLUE – Medium strength, can be disassembled with hand tools
GREEN-Retaining and Penetrating viscosity, High strength, Heat and hand tools are often required for disassembly.
RED – High strength permanent, Heat and hand tools are often required for disassembly

So, even if they have a lapse of concentration or a defaced label, the engineer can visibly see if they are using the correct product for their application.

Thread sealants for Pipes

Why are they normally white?  There are a couple of reasons

a) They look nice and clean and wholesome – especially when in contact with drinking water

b) They contain PTFE (like a liquid version of the tape we are all familiar with which happens to be white) to help lubricate the joint during assembly.

2-Part Epoxies

The majority of 2-component epoxies are two different colours. Epoxy resin and hardeners have to be properly mixed in their stoichiometric ratios. Black and white seem to be most popular, when mixed the adhesive should come out a dark shade of grey with no streaks.  The cross pigmentation makes it easy to see if the components are properly mixed or whether more stirring is required. It is important to use a good mixing technique, being too vigorous could entrap too much air.

Some applications require entirely white or entirely black epoxy so it is possible to use a clear resin in combination with a coloured hardener (or vice versa) to achieve the desired result. Epoxies can be colour matched to applications – e.g. a dark walnut automotive dash veneer may require a colour matched epoxy to bond it or a Caesar stone workbench may need a matching epoxy joint.

Heat Cure Epoxies

Available in a wide range of colours but favoured in a dark shade of grey or silvery in colour. This is because these high performance products are often used in place of welding, soldering or brazing. Despite adhesive often being stronger than welding or brazing it is often viewed as a recipe for disaster by non-engineers that suffer flashbacks of failed mug-handle or spectacle arm bonding mishaps. For this reason the adhesive joint has to look rugged like it is properly welded. The added benefit of using the correct adhesive instead of welding is better stress distribution, no damage to the substrate material, plus a 100% seal.


Normally these are clear and colourless. There are rubber toughened grades which are black but apart from these, cyanoacrylates don’t hold pigments in suspension well so do not come in different colours.

UV Curable Adhesives

These are generally clear as they need to maximise the UV light transmittance to facilitate cure.  Incorporating a colour into the formulation could be a disaster if it absorbs UV light as it may prevent any depth cure.  Coloured UVs normally have a secondary cure mechanism (such as anaerobic) to allow curing in shadow areas that UV light can’t penetrate.

For further assistance or help with selecting a suitable adhesive or to discuss your colour matching requirements, please contact Permabond.