I spent the last week of nice days spraying wood cleaner on 500 pickets (often with a one-year-old on my back). I used a different cleaner on the last third of the pickets and it discolored the wood a little. It doesn't matter since I'm using a solid stain. The point of the cleaning is to remove the the mill glaze (or scale) and open the pores so that the wood absorbs the stain.
