Which of the following is NOT a type of water-blasting technique?

Water-blasting techniques are primarily focused on using high-pressure water to remove contaminants from surfaces. Options such as grit blasting with a shroud, sand injected water blast, and slurry blast with a grit/water mix all involve the use of water as a medium to enhance the blasting process, whether by using additional materials like grit or sand in combination with water.

Air-jet blasting, on the other hand, involves the use of compressed air to propel abrasive materials towards a surface. This method does not incorporate water in its operation, which distinguishes it from the other techniques mentioned. Therefore, it does not fit within the realm of water-blasting techniques, making it the correct answer to the question regarding which option is not a type of water-blasting technique.