NHML Resources - Analytical Techniques for Paint & Coating System Failures

With the use of various chemical analytical techniques, we can identify paint and coating types such as epoxies, urethanes, acrylics and latexes. Causes of discoloration, contamination and degree of cure can also be studied. These analytical techniques and some common problems associated with coating system failures will be discussed here.

Gas Chromatography (GC)

GC is an analytical technique which separates and detects the individual components in a mixture according to their volatility (i.e. boiling point). Both cured and liquid samples can be analyzed by GC with appropriate sample preparation. By comparing chromatograms (plots of detected component vs. time) of an unknown or suspect sample with reference samples, identifications of materials can be made. This technique is useful in comparing paints and coatings with similar binder types such as acrylic oil based and acrylic water based paints or similar paints from different manufacturers.

Figure 1. Gas Chromatograms of two paints show major differences in their solvent systems - click to enlarge.

(Figure 1. Gas Chromatograms of two paints show major differences in their solvent systems - click image to enlarge.)

Fourier Transform Infrared Spectroscopy (FTIR)

FTIR can also be performed on either cured or liquid paint samples, and produces a chemical fingerprint which represents the interatomic vibrations of all molecules in a sample. Identification of paint or coating type can be made using this technique. Reference samples are not necessary if this is the only quality of interest.

Causes of staining or contamination can sometimes be identified by FTIR. In most cases, reference samples of uncontaminated paint and possible suspect materials are necessary.

Figure 2. FTIR spectra of an epoxy and an acrylic paint illustrate differences which allow identification - click to enlarge.

(Figure 2. FTIR spectra of an epoxy and an acrylic paint illustrate differences which allow identification - click image to enlarge.)

Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Spectroscopy (EDS) and Optical Microscopy (OM)

Using magnification, qualities such as coating layer thickness and porosity can be studied. SEM/EDS can also be instrumental in contaminant and pigment examinations in adhesion failure analyses.

Some causes of paint and coating failure are improper surface preparation, improper coating preparation, incorrect application and deleterious structural and environmental conditions. Using a combination of microscopy and analytical techniques, causative factors can often be identified in failed systems.

Some Examples of Cases Analyzed by Our Staff

Staining of an industrial paint was found to be due to an improper mix ratio of Part A and Part B in a two part epoxy system causing the excess amine curing agent to exude to the surface.

Application and performance problems with an industrial paint were found to be due to a vendor change in the solvent system.

A house paint proved to be the oil based paint specified by the homeowner.

Random samples from a concrete pier were tested for the presence of a surface waterproofing agent. It was concluded that the application was spotty and incomplete after analysis detected no water proofing agent on many of the samples.

Staining on treated decking was determined to be caused by dirt and biological growth, not iron filings left by a contractor as alleged by the homeowner.

Paints, specified as epoxies for a waterproof application, were identified as acrylics.

Blistering of a swimming pool coating was found to be due to a reaction of one of the coating ingredients with acidic water which produced an outgassing of carbon dioxide. The analysis proved the product and contractor at fault.

Leaking roof gutter caused poor adhesion of paint to siding.

Alkyd stain applied to new, moist, wood house siding caused an adhesion failure.

Shrubbery situated close to a house caused retained moisture which resulted in mildew formation and peeling paint.

The cause of peeling paint from galvanized steel was found to be incomplete aping of the metal surface before primer application.

To Obtain Samples

To insure collection of appropriate samples we recommend a phone call to our analytical chemist to discuss the problem, samples and analysis needs. If needed, sample containers will be sent to you since contamination from certain containers may be a problem in analysis.

For paint already applied to a surface, submit a sample of the coated substrate or chips of coating in question. Chips ranging from one eighth to one half inch in length or larger are needed.

For uncured paint, mix thoroughly before obtaining a sample unless the material of interest (i.e. the contaminant) is already separated out. Liquids from two part systems should be kept in separate containers.

V. Ridlon, W. Bartlett, 3/91

See our Industry Definitions for further insight.

 

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