50 Shades of Glue

Adhesive Color Explanation by Adhesive Type

Anaerobic Adhesive Colors

Maintenance Engineers often leave a trail of oil and grease around the job site 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 see the grade reference or part number on the bottle. However, most adhesive manufacturers operate a color-coding system for anaerobic threadlockers, which is recognized 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 see if they are using the correct product for their application based on the adhesive color.

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 colors. Epoxy resin and hardeners have to be properly mixed in their stoichiometric ratios. Black and white seem to be most popular colors. 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 colored hardener (or vice versa) to achieve the desired result. Epoxies can be color matched to applications – e.g. a dark walnut automotive dash veneer may require a color-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 colors but favored in a dark shade of grey or silvery in color. 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.

Cyanoacrylates

Normally these are clear and colorless. There are rubber toughened grades that are black, but apart from these, cyanoacrylates don’t hold pigments in suspension well. So these adhesives do not come in different colors.

UV Curable Adhesive Color

These are generally clear as they need to maximize the UV light transmittance to facilitate cure.  Incorporating a color into the formulation could be a disaster if it absorbs UV light as it may prevent any depth cure.  Colored 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 adhesive color matching requirements, please contact Permabond.