One of the most common misconceptions about HoldTight 102 salt remover / flash rust inhibitor is that it can be “sprayed on” or otherwise applied like a coating.
Sure, it is physically possible to do so, but its effect on the surface if used that way will be of little value. And if it is “put on” this way at full strength (i.e., without at least a 50 to 1 dilution -- potable water to 102) it will not evaporate and will become a residue that will be a problem for some coatings.
The key to using 102 effectively is to dilute it properly AND to pressure wash the surface with the water + 102 fluid -- we say “treated water” -- the more pressure the better but the water volume need not be greater than 1 gallon per minute -- a common flow rate for pressure washers. Higher pressure improves performance, higher volume doesn’t help add much.
Most off-the-shelf (at Home Depot or Lowes, for example) can easily generate 1500 p.s.i of pressure with a flow rate of 1 gallon per minute. Industrial washers can go much higher, 5,000 p.s.i or above and they are more efficient. Heating the water will improve performance, but is not essential.
Why are pressure and flow important? Simply because 102 is a washing agent, a surfactant, like soap, but UNLIKE soap, it leaves no residue if allowed to evaporate with the water that contains it. Forcing the water with the 102 into the profile or pores of the surface results in more thorough cleaning. When the surface is dry, the 102 is gone. There is nothing to remove. You are ready to apply your primer or coating or you can wait several days without seeing flash rust.