Protective Coatings / Concrete Sealing
Although concrete is known for it's strength and durability, it doesn't last forever. Maintaining a coat of sealer will significantly increase it's lifespan and keep it looking good. Sealers protect against the elements, especially in harsh climates where there are many freeze and thaw cycles throughout the year. When water penetrates the surface and freezes, it expands and breaks apart the concrete resulting in scaling and spalling. Sealer also protects the surface from any chemicals, especially acids, that may be spilled and makes cleanup easy. Think of your concrete as low maintenance but not maintenance free.
Exterior Surfaces
For almost all exterior surfaces,(patios, porches, driveways, sidewalks,garages,etc.) solvent-based acrylic concrete sealers are usually your best bet. These work well in both commerical and residential applications and will provide protection against the elements, most chemical spills, and stains. They will also give the surface a shiny look, which is desirable in most cases, and can really enhance the colors of decorative concrete.
Interior Surfaces
Acrylic concrete sealers are also the usual choice for interior floors as well. For homes that are finished or being lived in, I highly recommend using a water-based acrylic sealer. Solvent-based sealers give off alot of unpleasant and sometimes harmful odors which can really stink up the house and can be difficult to get rid of. Water-based acrylics, however, are almost odorless and much less toxic. Water-based acrylics will also create a glossy appearance which, again, is usually desirable. Keeping a coat of wax on top of the sealer will prevent the need of resealing in the future.
Deteriorating Surfaces
For surfaces that are showing signs of deterioration, such as scaling or spalling, penetrating concrete sealers are recommended. This type of sealer will work it's way down into the pores and capillaries and fill them in with a cement-like material. This almost completely seals the concrete from water or any foreign substance penetrating from the surface or the underside. Penetrating sealers will actually strengthen the concrete itself and greatly reduce the rate of deterioration. Also, penetrating sealers won't leave a shine on the surface which makes them a good choice if a glossy appearance isn't desirabale.
Decorative Concrete
Solvent-based acrylic sealers are the most suitable for decorative concrete finishes whether it's stamped, colored, stained, etc. They can really bring out the colors and textures when applied. This is especially true of acid stained surfaces. The difference is almost night and day between sealed and unsealed acid stains. Acrylic sealers can restore the look of decorative concrete to almost new.