Sand blasting is the process of roughening and cleaning the surface of old and set concrete (or in any corroded steel surface) by means of coarse sand and air applied under pressure of 90 to 100 pounds per square inch (6.33 to 7.03 kilogram per square centimeter) through a nozzle, so as to erode the laitance and grout from the old and fresh concretes monolithic.
Sand blasting of rock is also done so that concrete may be placed on or against a clean surface as required according to specifications.
There are two types of sand blasting, namely “wet sand blasting” and “dry sand blasting“. In wet sand blasting water is also used along with sand and air under pressure, while in the latter, only sand and air under pressure are used. Normally the concrete and rock surface etc., are wet sand blasted to keep down the dust.
The percentage of different sizes of sand particles for efficient sand blasting shall be as follows:
8 mesh per inch (25.40 mm)
16 mesh per inch (25.40 mm)
30 mesh per inch (25.40 mm)
50 mesh per inch (25.40 mm)
For effective sand blasting it is essential that pressure of air should be between 90 to 100 pounds per square inch (6.33 to 7.03 kilograms per square centimeter). If pressure falls below 90 pounds per square inch (6.33 kilograms per square centimeter), sand blasting becomes in effective. If sand having large percentage of fines is used, it will not provide the requisite cutting power and the whole effort goes waste. A good quality well graded “sand-blast-sand” is needed for achieving the objective of sand blasting.