What does acid etching do to concrete?
Etching a concrete disolves the lime in the concrete! The bubbles on a surface when an acid is introduced demonstrate that the lime is being attacked. Lime is the Bond for aggregates in the concrete that bind the concrete together. Most acid etching calls for a diluted mixture that only harms the surface. The sand that is visible on a surface after an acid wash is nothing more than the fines in the mix that came un bonded from the concrete.
It is said, to Open the capillary/gel-pore structure allowing for a better bond? Paint & Coating people like it because they feel it will make their products adhere to a concrete better. Which it does for a limited time! Failures of a coating after application to an etched surface are usually caused by chemicals that migrate Out of that Opened capillary system to collect under the coating, causing it to blister, loose the bond and peel off. Along with,this "Mechanical Adhesion" method, comes the side effect of enhancing chemical migration out to a surface, that causes even more long term problems. If the intent is to offer a rough textured profile for adhesion purposes, a Much better solution is sand blasting to mechanically abrade a surface.
After sand blasting, application of a penetrating sealer is recommended. StableCrete is a product that penetrates Into the capillary/gel-pore structure, waterproofing the concrete, providing a superior bond of any coating or mastic. http://www.StableCrete.com provides answers to prevent moisture transfer in or out of a concrete. Once Waterproofed, internal chemistry does not migrate out causing problems. A Waterproofed concrete also does not allow moisture and contaminates to enter, creating corrosion cells on embedded steel members [Re-Bar].
Acid Etching is commonly used because it is less expensive than other methods, however it comes with a price! It certainly, is Not Green and can be a very dangerous proposition for you and your concrete!