Concrete efflorescence is a white powder that is is found on the concrete surface. It is caused by the water from underneath the concrete migrating up the slab, once it reaches the top, the water will evaporate and leave salt particles on the surface. The white efflorescence powder will be soft at first but eventually will turn hard.
If the efflorescence is left on the concrete for long periods of time it will eventually start to eat into the concrete leaving the concrete with a lot of divots and pits as you can see in the photo below. The concrete will then have to be repaired.
There are two types of sealers we have used that have stopped efflorescence. One type is an epoxy vapor solve product that will basically seal off the concrete completely not allowing the water to escape. This product is best used if you are going to be putting another type of flooring on-top of the concrete that is not breathable such as laminate flooring, VCT, or wood. The epoxy coating can also be used if you want to clean up the look of the concrete if it is going to be left alone. Applying concrete coatings is best left to the professionals because of the proper surface profile needed for the coating to bond properly.
The other type of sealer we have used is a cost affective DIY alternative to the epoxy vapor solve product. It is a penetrating sealer that will not change the look of the concrete and will still allow the water to pass through the slab. It is not used if you are trying to completely eliminate the moisture coming through the slab. This type of sealer will only stop the efflorescence from forming. It can be used on concrete and bricks. The concrete will need to be cleaned and all of the efflorescence removed from the surface before applying the sealer.
The pictures above are of a garage floor that had serious moisture problems. Water was seeping through the concrete pooling in the middle of the garage. Efflorescence was starting to form causing the concrete to pit. We were called to restore the concrete; we prepped the surface and then applied a tinted vapor solve epoxy system followed by a top coat of polyurethane.