If soluble chlorides are present at the substrate bondline they may accelerate the set of the overlayment near, or at, the bondline and have a negative effect on the bond strength. Etching solutions react with the calcium compounds in a process called neutralization which produce chloride salts. These must be completely removed in order to assure adhesion. It is important not to etch if the slab is less than 28 days old, doing so will expose an excessive amount of the aggregate, surface will be to rough, and the top layer of the concrete will be compromised and weakened. Scrub with push broom, rinse thoroughly, allow to dry, then PH test for neutralization.
Steel shot is propelled at the surface at high speeds.
The impact breaks down the surface. Shot and debris are suctioned up into an air stream chamber. Dust is drawn up by a vacuum and steel shot is reclaimed. Although it is best to hire a professional since using the wrong size shot can damage the substrate, many of the shot blast equipment manufacturers now lease,, or rent them out by the day and will guide you on their usage. Planers, milling machines, and rotating cutters are all classified as scarifiers.