Wet Sponge Test

Last updated: November 17, 2016

What Does Wet Sponge Test Mean?

A wet sponge test is a testing technique used to locate discontinuities in coating film. It is suitable for finding pinholes through a non-conductive coating and a conductive substrate.

This testing technique is economical and easy to perform in the field and causes no damage to the coating surface. This testing method is also considered non-destructive. This technique is ideal for measuring insulating coatings less than 500µm (20mils) on conductive substrate. A low voltage wet sponge test is mostly popular in the coating industry. The low voltage sponge method is also ideal for powder coatings and other coatings where the user does not wish to damage the coating.


Corrosionpedia Explains Wet Sponge Test

Wet sponge technique is a technique for locating pinholes or cracks on the coating surface by applying low voltage to a moist sponge. In this technique, the sponge moves over a coating flaw, liquid penetrates to the coating substrate and low voltage completes an electrical circuit, sending a signal to the detector and sounding an alarm. A sponge is moistened with a wetting agent and is supplied with a low voltage. Tap water can be used to moisten the sponge because it contains electrolytes that keep its electrical conductivity relatively high.

The wet sponge technique provides a procedure for electrical detection of minute discontinuities in non-conductive coating systems. Discontinuities in a coating are frequently very tiny and normally not visible with the naked eye. The wet sponge technique is able to detect pinholes, cracks and damaged areas on non-conductive coatings on conductive substrates. If these flaws are not addressed, they will eventually lead to corrosion and premature failure of the coating.

There are two types of wet sponge test:

  • Low-Voltage Wet Sponge Test: This is generally used for evaluating the existence of discontinuities in coating films with a total thickness of 0.5 mm (20 mil) or less.
  • High-Voltage Spark Test: This is used for determining the existences of discontinuities in coating films with a total thickness of greater than 0.5 mm (20 mil).

If high-voltage spark testing equipment is used to determine coating discontinuities at a thickness of less than 0.5 mm (20 mil), it may damage the coatings as well as equipment.


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