Why do some sealants go yellow?

Some sealants go yellow because they don’t have sufficient UV protection incorporated into the formulation. UV light has the ability to turn people red and tan, but unfortunately, it also has the ability to turn white sealants yellow, and grey sealants green... 

There are actually three reasons why a sealant may go yellow: 

  1. Insufficient UV protection incorporated into the formulation
  2. Cured in the dark 
  3. UV protection has been chemically damaged or washed out 

Insufficient UV protection is normally only found at the very budget end of the adhesive market, the no frills own brand products that cost peanuts... you pay peanuts – you get monkeys, or a white sealant that turns yellow in sunlight. 

Yellowing Sealant from UV Light

Cured in the dark – Have you ever noticed with some gloss paints, they go yellow where they have been kept in the shade or in the dark. Some UV blockers actually need UV light to activate and protect the sealant. Two simple fixes here – Allow the light in or buy a better sealant. 

Yellowing on sealant from being cured in the dark

UV Protections has been chemically damaged or washed out – This is surprisingly common. So many adhesive suppliers try to assist their customers in getting a smooth seal on their products by offering degreasers, solvents or other harsh chemicals. This can damage the sealant in many ways, including washing out the UV blockers (hence it goes yellow), washing out the polymer (making it significantly weaker) and washing out any fungicides (these stop mould growth). Another problem caused by using these types of solvents and degreasers is it leaves a weak surface which is readily washed away exposing the fillers and other components. This then becomes a magnet for dirt entrapment at a microscopic level. 

UV Degradation on a sealant

Want to know the best and safest way to get a good finish on an MS polymer? See our article here: How to get a good smooth finish with an MS polymer