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Industrial Flooring Problems Part 9: Yellowing and Cloudiness

  • Industrial Flooring Problems Part 9- Yellowing and Cloudiness

Industrial Flooring Problems Part 9: Yellowing and Cloudiness

Sometimes an epoxy topcoat will develop an unwanted yellow hue. This is a problem that can affect epoxies regardless of whether it is a clear system or not and will typically be because of one of the following reasons:

Causes of Yellowing in Resin Floors

  • Direct sunlight is usually the most common cause of a floor yellowing and losing its gloss, as the yellowing process is accelerated by exposure to UV light.
  • Using resin flooring material that is past its expiration date.
  • Improper storage of the product. Resins and hardeners need to be stored in a cool, dry place away from sunlight and with a stable temperature.
  • Epoxy yellows after curing when exposed to water, moisture, excessive heat or the sun.

Once yellowing has occurred it is very difficult to repair and in most cases the floor area will need to be completely recoated.

Preventing Yellowing in Resin Floors

Consider putting down a clear, UV resistant and non-yellowing sealer over the epoxy floor, as this will make it much easier to clean, will resist stains and will protect against fading and discoloration.

Often epoxies are top-coated with a clear aliphatic (non-yellowing) urethane sealer, which is a two-part polymer that hardens just like epoxy and when used as a sealer will help to retain the epoxy floor’s colour and attractive gloss.

One other way to minimise the impact of yellowing is to select pigmented epoxy colours that are dark or that contain a lot of yellow (such as green) to begin with.

Causes of Cloudiness in Resin Floors

One other undesirable type of discoloration is when an epoxy coating appears white or cloudy immediately after installation or curing.

This is usually caused by the resin floor being exposed to water prior to it completly curing. Moisture in the concrete substrate or high levels of humidity can both result in sufficient amounts of water being present to affect a resin finish in this way. This can result in a “milky” or “greasy” film, which is sometimes referred to as a “blush” or “amine blush”.

A milky or cloudy appearance can also be the result of the product being applied too thick and will be more noticeable if the coating is clear.

Preventing Cloudiness in Resin Floors

It’s important to monitor the moisture levels in the substrate as well as the humidity levels before applying a coating. Be sure to check the Product Data Sheet for the system in question to find out the maximum amount of relative humidity (RH) that can be present in the substrate as well as the recommended material thickness.

If cloudiness does occur it may be possible to repair the affected area by diamond grinding the compromised coating, reapplying according to the Product Data Sheet’s recommendations and if the surface appears greasy wipe it with Denatured Alcohol.

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Dan Ash

Daniel Ash is the PR & Media Manager at the global resin flooring manufacturer Flowcrete Group Ltd. Dan's role includes creating press releases, blogs, white papers and case studies on Flowcrete products and projects as well as educational content for construction industry professionals.

4 thoughts on “Industrial Flooring Problems Part 9: Yellowing and Cloudiness”

  1. kelly feetenby says:

    Hi i have laid a epoxy white metallic resin floor and applied a UV sealer but the floor yellowed almost straight after, no direct sunlight can hit the floor and i had a gazebo against the window when installing, the floor is yellowing more and more each day, can you give me some advise to why this may happen?
    many thanks kelly

    1. Dan Ash says:

      Hi Kelly
      It sounds like it could be a blooming issue (if moisture has got into the resin while the floor was curing) which can cause rapid yellowing. We’ve got a few posts that go into more detail on this ( and and this PCI article is also quite informative on the issue ( Unfortunately if it is blooming then there’s only a few options available to fix it (the second blog post I’ve linked to goes into more detail on these options).

  2. alex astor says:

    I epoxy coated 2000′. Immediately it looked great…. for days actually. Now almost a week after the coating, it is turning very cloudy.
    I took some soap and water and scrubbed about 10 sq feet. It instantly came back to the brilliant blue. However as soon as it dried, it went back to the hazy milky color.
    I used 4 separate 5 gallon kits. 2 of the kits are still great. 2 are milky.
    Floor was prepped for 3 days with a diamond grinder. Blown off many times before I applied the epoxy. Humidity was below 80%.
    A) What caused it
    B) I guess I need to sand and then apply clear coat?
    Thank you

    1. Dan Ash says:

      Hi Alex
      This does sound like it could be an amine blush issues. However it may not necessarily be a humidity issue, can you contact the manufacturer to see if they have retained batch samples that can be tested? As this could help to determine if there was a problem with the batch itself. It might be possible to restore the colour with a metalized polish (such as with Enhance acrylic polish) applied in 2 to 3 applications and then maintained using this metalized polish. You could go down the route of applying a clear gloss sealer coat, however this needs to be suitably trialled in an inconspicuous area first to check its compatibility, with an additional bond test using a bond tester.
      Hope this helps.

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