It is always a good idea to do your research when buying a concrete sealer. However, you will be taken back by the multitude of information available online about concrete sealers. One brand will claim to do this, another brand will claim to do that but keep in mind every sealer is different for every consumer. Some projects will require a penetrating sealer while other projects will require a coating or an epoxy system. Other factors include location (temperature, weather and condition of the slab.) The proper application will vary depending on the different project parameter.
To put it simply, we can break concrete sealers down into two categories: penetrating sealers, or concrete coatings. Concrete coatings, also known as acrylics, epoxies and urethanes, are solutions that are made up of larger sealing particles. These large particles will not fit through the tiny pores or penetrate through the surface of concrete. Instead, they will remain on the surface, acting like a raincoat for the concrete to help resist water. Of course, like a raincoat they will not keep water out indefinitely; they are simply water resistant, not waterproof.
Penetrating sealers on the other hand consists of silicates, siliconates, silane/siloxanes, or a blend of the above. These sealers are densifiers, hardeners, water repellents and help to reduce mold, mildew and efflorescence. With the smaller particle size these sealers are able to penetrate and chemically react with the concrete forming calcium silciate hydrate or a hydrophobic barrier preventing the passage of water. All the hairline cracks, voids and pores of the concrete are sealed creating a stronger, denser concrete slab.