Dirty terra cotta porch
Terra-Cotta floor tiles are made with Adobe clay that is than heated to increase it's strength. It is a popular choice for a floor covering because of it's durability. But if not sealed properly can develop stains (mold, dirt, etc.) which are difficult to remove because of it's porosity. An analogy would be it's comparable to a dried sponge (but harder). Once the seal is worn away it will absorb any liquid on its surface. Power washing is one way to clean the tile, but the spray pattern must be very wide to avoid eroding the tile. And it must be kept moving for the same reason. If mold, fungus or algae are the problem first make a bleach solution in a five gallon bucket (1 cup bleach and 4 gallons water). Mop the solution liberally onto the floor and scrub vigorously into the problem areas. Wait a few minutes and either power wash the surface or apply clean water and mop up as much as possible. A floor scrubber works well to, but not with an aggressive brush. The tiles must dry completely. The drying time can be sped up with fans and/or heaters. And depending on your climate should dry in 2 (+/-) days. With a paint roller and brush apply an exterior Terra-Cotta floor sealer according to the manufacturer's directions'. It should be ready for foot traffic between 12 - 24 hrs.