Analysing Paint Problems
When problems occur on site they can normally be associated with the following elements:
Specification employed, substrate conditions, weather/ internal environment, application methods, materials usage.
In the majority of cases most problems should be relatively straight forward to resolve. However, if they cannot then it may be necessary to seek a third party involvement.
Case History.
The last applied coating had after a relative short period began to show signs of cracking and flaking. The client would not accept the decorator’s opinion that he was not at fault.
Under the circumstances as a substantial monitory sum was involved both parties agreed to obtain the services of an independent consultant and both parties agreed to accept the findings and recommendations.
Site visit.
The first step was to carry out a site visit and assess the situation. At this time a visual examination of the problem was made and a sample of the defective paint film removed for examination.
Examination
When the dry paint flake was removed from surface it was brittle and the coating left on the surface was powdery/under bound in nature. (Distemper). This under bound coating was also attached to the rear of the paint flake.
The removed sample measured an overall film thickness of 708 micrometres and was recorded.
The under bound coating, firmly attached to the reverse side of the paint flake was easily removed when washed and taken back to a firm washable surface.
The film thickness was again measured and recorded as 427 micrometres resulting in 281 micrometres of the powdery material being removed.
35 micrometer is the average film thickness of modern paints. The cross section of the paint film removed shows the number of coats and the film thickness of each.
Conclusion
The problem encountered is due to the combined tensile strength and film weight of other coatings applied onto the original powdery/under bound material. The initial coat applied to the under bound surface has limited adhesion properties. Therefore this along with subsequent coatings has aged meaning that the overall tensile strength of the paint film is greater than the adhesion of the initial coat. Cracking, crazing and flaking has occurred.
Note: The difference in colour shown of the original sample taken off he wall and the other samples shown was due to the artificial lighting.
See specification/distemper.
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