Prior to washing down crack control joints should be installed at this stage. These should be cut with a circular diamond-edged blade. Cuts should be at least a quarter of the thickness of the slab deep, and there should be one every 20m2 dependent on shape.
During the summer washing down can usually be done after 24 hours, in the winter it is best left for 48 hours to ensure no damage is done to the finished surface.
The release powder has a waterproofing agent as part of its makeup, it also contains a colour pigment. This has the effect of either antiquing the colour or adding a variation to the base colour, most natural stone, slate etc have more than one colour, therefore, release agents add to the natural finished look.
Power washing is the most effective way of removing the powder and getting the waterproofing agent out without removing too much pigment. It is important that the waterproofing agent is removed as it would inhibit the sealer from getting into the surface of the concrete. Should too much pigment remain in the concrete after power washing, then specialist cleaning formulas such as a pre-wash can be used. A solution of ordinary patio cleaner in water can also be used, only a capful of patio cleaner to a bucket of water will do.
Note that some people will use washing up liquid, while this will also do the job, you must be careful as squirting it onto the concrete neat can stain the surface.