Wet Sponge Testing is similar to High-Voltage ‘Spark’ Holiday Testing. It applies a direct current to a sponge probe and detects holidays on a coated or lined surface. This method is less intrusive than High Voltage Testing and is a good holiday detection method for items with lower dry film thickness coatings.  This method of holiday detection can only be carried out on non-conductive coatings.

Why is Sponge Testing Important?

Some coatings and linings can be sensitive to high voltage testing, furthermore, in some cases, high voltage testing is also unnecessary.  Wet sponge testing is a convenient and low-cost alternative for thinner film thicknesses and is a more than adequate alternative to dry spark holiday testing.

How does Low Voltage Holiday Testing Work?

The inspector places the sponge of a handheld, low voltage device (typically between 9V and 90V) in a surfactant/water mixture and squeezes excess moisture from the sponge.

The absorbed water mix contains electrolytes – minerals that allow an electrical circuit to form when they create a bridge between a conductive substrate and the end of the probe. As the sponge travels over the coating or lining film, the water penetrates any voids, pinholes or holidays, which is then detected by the low voltage device, sounding an audio or visual alarm.


  • Less intrusive than high voltage testing
  • Handheld, easy to operate device
  • Units run on standard AA batteries
  • Less likely to cause cosmetic and functional damage to the coating or lining
  • Safer to use than high voltage device


  • Not suitable for heavy-duty, thick coatings or linings

Next steps

At KUE Group, we carry out a range of surface treatment and preparation services for industrial clients across the UK and Europe. To discuss your requirements with one of our engineers, or to request a free quote, get in touch by phone on 01274 721188, or email