Sealant Varieties: Solvent or Acrylic Based
There are many varieties of sealants currently on the market. Some are solvent based (petroleum based), while others are acrylic based (water based). Some are clear, while others are colored. You have many to choose from.
Some sealants penetrate into the concrete, while others merely create a film on the surface. The penetrating sealers generally perform much better. Try to use a penetrating sealant, if at all possible.
Some sealants have compounds in them which virtually prohibits water from being absorbed by the concrete. In certain instances, these sealants also inhibit the passage of water vapor from the slab to the air above the slab. These sealants are often referred to as non-breathable. This property can be detrimental depending upon the climate. Sealants containing compounds which do not breathe should be avoided in climates where temperatures drop below freezing (32 F) for extended periods.
The reason for this is quite simple. Concrete slabs can absorb water from two directions. They can absorb water from rainfall or surface runoff on top of the surface, or they can absorb water from the soil beneath the slab. The water from beneath the slab is actually drawn to the surface as water vapor. Without a sealant, this water can evaporate from the surface.
However, if you seal the concrete with a non-breathable sealant, a barrier is created which the water vapor cannot easily penetrate. During cold weather, this water vapor can freeze and cause the surface of the concrete to flake. There are sealants which contain compounds which allow them to breathe. Often these sealants are clearly labeled as to whether or not they do, in fact, breathe. Consider using these if you live in a cold climate.
Before Using a Sealant
When using sealants, it is EXTREMELY IMPORTANT to follow the manufacturer's directions and instructions. I can't emphasize this enough. Read the directions carefully before opening the product. Pay attention to the air temperature. When the manufacturer says the concrete should be clean and dry, they mean it. If in doubt, clean the concrete with soap and water using a stiff push broom. Thoroughly rinse the surface to remove dirt, soap, etc. Let the slab dry, possibly for a day or two, to ensure that it is totally dry. Generally, the best time to do this type of work is during the summer months. This way you can let the hot sun dry the slab quickly and thoroughly.
Also, WEAR PROTECTIVE CLOTHING and/or EYE WEAR when dealing with these sealants. They can harm your skin and eyes. Avoid using petroleum based sealants indoors, due to the possibility of fire or explosion hazards. These products generate flammable and/or explosive fumes as they dry. BE CAREFUL!