Yeah what he said!

Basically that is it, some folks do it after decaling I have had some bad reactions so I do not, just some post weathering after decaling to blend stuff together. Also it can be a bit of a crap shoot I have seen some go bad so that the whole kit will need to be repainted. So typically I will do it after base coat.

For me I am trying to get that grimy look planes get on carriers due salt, cramped quarters etc for this am using very very very thinned mixture of well thinner, Tamiya Smoke, Gunze Soot and the darkest grey that I used on the plane.

As for the salt application I just airbrush tap water over it and apply salt with a salt shaker, I put it on pretty thick (remember to put it back or the wife will start asking questions about how much sodium you are taking in). After all is dry I either rinse off in the sink or with the aribrush

The other this I typically at least 2 rounds of this to ensure things are randomized. 

Rob