Surface preparation is an important part of the coating inspection process, but visual assessment of a prepared surface does not necessarily provide information about soluble salt contamination. Soluble salts can be present on a substrate following exposure to marine, industrial or other environments, and their presence may need to be considered as part of the overall surface assessment. For this reason, salt contamination testing can form part of an inspection programme alongside other checks such as surface cleanliness, surface profile and climatic conditions. The appropriate test method and acceptance criteria will depend on the project specification and applicable requirements. Where quantitative measurement of soluble salts is required, the Elcometer 130 Salt Contamination Meter provides a method for measuring soluble salt levels on a surface using conductivity measurement.

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Soluble salts are ionic contaminants that can be present on a surface and can originate from a number of environmental or process-related sources. Coastal and marine environments, industrial atmospheres, contamination during handling, and residues associated with surface preparation can all be considerations depending on the substrate and working environment. The important point for an inspector is that surface appearance alone may not indicate the presence or level of soluble salt contamination. Testing provides a way of obtaining a measurement that can be compared with the requirements established for the particular project. A soluble salt measurement system such as the Elcometer 130 can be used to quantify surface contamination through conductivity measurement, providing an additional measurement alongside the inspector's wider surface preparation assessment.

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A common approach is to extract soluble contaminants from a defined area of the surface using a wetted test medium and then measure the resulting solution. The conductivity of the solution can be related to the amount of soluble ionic contamination present. With the Elcometer 130 procedure, high-purity filter paper is wetted with distilled water and placed against the test surface using a magnetic disc. The paper remains in contact with the surface for a defined sampling period before being transferred to the gauge for measurement. The instrument then provides the resulting reading. The Elcometer 130 incorporates the sampling process into its measurement workflow and includes a two-minute timer to help manage the sampling period. Its pressure plate is designed to provide consistent pressure between the paper and measurement contacts.

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The measurement is dependent not only on the instrument but also on how the sample is collected. Factors such as the area being tested, the test medium, the contact between the test paper and surface, the amount of water used, and the sampling time can all form part of the test procedure. A consistent sampling approach is therefore important when measurements are being taken across different areas or when results need to be compared. Inspectors should follow the relevant test method and project requirements rather than treating the instrument reading independently of the sampling procedure. The Elcometer 130 uses a defined 110 mm diameter sampling area, high-purity test papers and a 1.6 ml water sample. Its supplied magnetic disc helps position the test paper against the surface, while the gauge includes a two-minute sampling timer.

Conductivity is a measurement of a solution's ability to conduct an electrical current and is influenced by the concentration of dissolved ions. In a soluble salt test, the contaminants extracted from the surface contribute to the conductivity of the test solution. Depending on the instrument and test method, results may therefore be presented in different units. Understanding which unit is being used is important when comparing readings against a project specification or inspection requirement. The Elcometer 130 Model T can display measurements in several formats, including μg/cm², mg/m², μS/cm, mS/cm, ppm and percentage salinity. This gives inspectors the option of working with the measurement units relevant to their reporting or inspection requirements.

Consistency in surface contamination testing involves controlling as many parts of the measurement process as practical. Using the same sampling approach, defined test area and appropriate test materials can help make measurements more comparable between different locations. Environmental factors can also be relevant. Temperature, for example, can influence conductivity measurements, so compensation may be required as part of the measurement process. Inspectors should also consider calibration and verification requirements when establishing their inspection procedure. The Elcometer 130 incorporates automatic temperature compensation and is supplied with calibration verification tiles. The instrument also uses a pressure plate to provide consistent pressure on the test paper during measurement.

There is no universal number of test locations that applies to every coating project. The appropriate sampling plan will depend on factors such as the size and condition of the surface, the environment in which the substrate has been exposed, the project specification and the applicable inspection standard or procedure. An inspector may therefore need to consider whether testing should be distributed across different areas of the substrate rather than relying on a single measurement. Where conditions may vary across a structure, a suitable sampling strategy can provide a more representative set of inspection data. For inspectors carrying out multiple measurements, the Elcometer 130 can store readings in batches, with the Model T capable of storing up to 100,000 readings across up to 1,000 alphanumeric batches. This provides a way to organise measurements according to the inspector's chosen recording structure.

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Inspection records need to provide enough information for the results to be understood in the context of the work being inspected. Depending on the project, this may include the test location, reading, date and time, test method and any relevant observations. Electronic recording can also be useful where numerous measurements are being collected across a structure or project. Organising readings into identifiable batches can make it easier to distinguish measurements from different areas, stages or inspection activities. The Elcometer 130 stores individual and batch readings with date and time stamps. On the Model T, readings can also be transferred via USB or Bluetooth to compatible devices and ElcoMaster software, supporting integration with digital inspection records.

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The standard or test method used for soluble salt contamination should be established from the requirements applicable to the project. Specifications can identify particular standards, measurement methods, units or acceptance criteria, so inspectors should refer to the relevant documentation before carrying out testing. It is also important to distinguish between the capability of an instrument and the requirements of a particular inspection procedure. An instrument may support a specified measurement method, but the inspector still needs to follow the applicable procedure and project requirements when collecting and interpreting results. The Elcometer 130 is listed by Elcometer for use in accordance with national and international standards and specifically references SSPC Guide 15. The product documentation provides further information on its measurement capabilities and intended use.

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Instrument selection is only one part of establishing a suitable salt contamination testing process. Inspectors may need to consider the measurement range, resolution, sampling method, calibration and verification, data storage, reporting requirements and the practical conditions in which the equipment will be used. Field conditions can also influence the choice of instrument. A portable design, controls that can be operated while wearing gloves, resistance to dust and water, and the ability to store or transfer measurements may all be relevant considerations for inspectors working across different sites. For inspectors assessing these requirements, the Elcometer 130 Salt Contamination Meter combines soluble salt and conductivity measurement in one handheld gauge. The Model T offers additional measurement units, larger data storage capacity, USB and Bluetooth connectivity, and compatibility with ElcoMaster software and the ElcoMaster Mobile App.

Read more: Explore the Elcometer 130 Salt Contamination Meter

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