TECHNICALNOTESCOLOURFADING

WHATISCOLOURFADING?

“Fading”isdefinedinAS/NZS2310:2002Glossaryofpaintandpaintingterms”as“Thelossofcolourofoneormoreofthecolourpigmentswithinthepaintfilm”.Prematureand/orexcessivelighteningofthepaintcolouroftenoccursonsurfaceswithconsistentlyhighexposuretosunlight.Fadingorpoorcolourretentioncanalsobearesultofthe“chalking”processofthecoating.

Colourchangeduetofadingisanaturalandexpectedformofpaintdegradationhoweveritcanalsobeeasilyconfusedwithorexacerbatedbyotherissues,suchasenvironmentalcontaminationwhichwillalsocauseanoticeablechangeinappearance.

Overtime,mostcolourswillfadeorlosetheirintensitytoavaryingdegree,dependinguponhowmuchexposuretoharshatmosphericconditionstakesplaceduringthelifeofthecoatingsystem.

AsstatedinAS/NZS2311:2009,1.6.2.4(c),“Degradationofpaintisparticularlyrapidintropicalareasmakingtheexteriorgradelatexpaints,whichhavegreaterflexibilityandslowerchalkingrates,particularlysuitable.”Section2.1.3coveringDurabilitynotes“Darkcoloursinexteriorsituationsincreasetheabsorptionofheatandthismayhaveadeleteriouseffectonthepaintcoatingsandsubstratematerials.”

HOWDOESITOCCUR?

Factorsandconditionsbeyondthecontrolofthemanufacturerorapplicatorareknowntoacceleratesuchbehaviourinexteriorpaintsforexample:

1. Sunlightandultraviolent(UV)radiation:Fadingoccursmorequicklyinexteriorenvironmentswherethepaintedsurfaceisexposedtohighlevelsofsunlightoveranextendedperiod*.Radiationemittedbythesunintheultraviolet(UV)andnearinfrared(IR)regionsmaybeabsorbedbypigmentswithinthecoatingandstrongabsorptionofthesewavelengthrangescanappearvisuallyasfadingofthepaintfilm.

2. Hot/coldtemperaturecycling:Thegreatertheextremesoftemperature,thegreaterthestressonthecoatingsystemwhichcausesthepaintdegradationprocesstoaccelerate.

3. Applicationofdarkercolouredpaint:DarkercolourstendtoabsorbmoreheatandUVradiationtherebyputtinggreaterstressonpigmentspresentinthecoatingresultinginquickerpaintdegradation.

4. Coastalenvironments:Thecombinationofsaltandatmosphericmoisturecreatesacorrosiveenvironmentandconstantexposurewillcausecoatingtostartshowingsignsofdeterioration(e.g.fading)morequicklythanotherwiseexpected.

5. Correctfilmthickness:ProductapplicationatlowerthantherecommendedfilmthicknesscanacceleratetheageingprocessofthecoatingsystemallowingmoreUVtopenetratethroughthefilm,causingittodegrademorequicklyandchangecolour.

6. Over-tinting:Addingtinterstoawhitepaintthatisnotintendedfortintingorover-tintingalightordeepbasecantriggerfadingproblems.

7. Wrongproduct:Usingapaintthatisdesignedforinterioruseonly,foranexteriorapplicationisverylikelytoundergounwantedcolourchangeissues.

PREVENTION

Tominimisethe“colourfading”effect:

I. SpecifyandapplypaintproductsandcoatingsystemsthatareacknowledgedbythemanufacturertobeUVresistant.

II. SelectlightercoloursingeneralastheytendtoabsorblessheatandUVradiation.

III. Selectcoloursbasedoninorganicpigmentsand/oroxideswhicharegenerallymoreUVresistant.

IV. Establishedamaintenanceprogramfromthestarttoensurethatthepaintedsurfacesarewashedannuallyandrepaintedwithinapredeterminedtimeperiod.

Unfortunately,colourchangeduetothe“fading”effectisirreversibleonceitbeginstooccurandthecolourcanbeoftenquiteirregularorpatchyinappearance.Toeliminatetheeffecttheentiresurfacewillneedtobepressurewashedand/orscrubbedwithanon-metallicscouringpadtoremoveallsurfacecontaminantsandchalkingpriortorepaintingwithanapprovedcoatingsystem.Seekfurthertechnicaladvicewithregardstomorefaderesistantcolours.

REFERENCES

*AustralianStandardAS/NZS3730.20statesthattheexpectedlevelofperformanceis“moderate”discolourationafter24months(testedasperAS/NZS1580.481.1.2).