The waterblasting process delivers water as an abrasive material under high pressure. By using an ordinary pressure washer (Alto Dynamic X-tra, Kew Technology, Type P406) with adjustable water pressure up to 150 bars, surfaces of uncemented and weakly cemented sedimentary carbonates are cleaned rapidly with outstanding results. Different nozzles can be mounted onto the pressure washer. Some nozzles fan out the water to cover a wide area resulting in a gentle cutting action. The angle of spray should be kept at 90 degrees to avoid grooves within the sediment surface. By moving the nozzle back and forth over a surface, matrix is removed and macrofossils may be exposed in situ.
Other nozzles have tight spray patterns suitable for deep cutting. Prolonged cleaning of the samples can result in a complete disintegration of the sediment, so the fossil remains can be extracted for study without any evidence of abrasion. Cutting by the pressure washer can be varied by adjusting the water pressure, thus raising or lowering the velocity of the water stream, or by changing nozzles, thus altering the spray pattern of water emitted.
Subtle cleaning of macrofossils may require lower water pressure than provided by the ordinary pressure washers. This type of cleaning may be facilitated by using a hand-held watergun (Wagner Model W 400 SE) with adjustable water pressure up to 180 bars at 10 mm from its orifice. For even more delicate cleaning, the Paasche airbrush (Model VL #3) is useful because of its smaller size when delivering a water stream at about 8 bars. By adding carborundum powder (1000 grit) to the water, the effect of blasting may be increased by a factor 10 to 20. Adding a few drops of detergent may ease the suspension of the powder. Because the suspended powder is covered by a water film, the technique is much less abrasive than sandblasting. The water film functions like a cushion around the powder grains.
Safety notice: never point the blasting equipment toward people. Safety glasses and gloves must be worn. The sample should be secured tightly before blasting.