Zero issues controlling where the foam goes. Easy as can be IME.
I gotta write up my wash technique some time...I know, I`ve been saying that for years
-Rinse (preferably pressure wash) vehicle
-Spray foamgun output on vehicle
-Spray foamgun output on wash medium that`s already soaked with shampoo solution
-Touch wash medium *very lightly* against vehicle
-Move wash medium a short distance across paint using an interrupted "jiggling" motion while spraying foamgun output at/directly ahead of the point of medium-to-vehicle contact. Yes, it takes a little acclimation (I got pretty dialed-in after maybe three dozen washes, though I`m always refining it even after all these years)
-Rinse area and wash medium, inspect, repeat..if done correctly it`ll be so gentle that one pass will *NOT* get most things perfectly clean
Notes:
-Replace foamgun`s pistol grip with something easily operable with thumb (I use a full-flow shutoff)
-Mix up gallon(s) of foamgun solution and (re)fill foamgun with that (I use ~7oz. shampoo : ~121oz water = ~1gallon)
-DO NOT expect foamgun to completely eliminate need to rinse out wash media, though it *might* work that way with a BHB depending on your water pressure
-I find that the "rinse" setting on the foamgun is less effective than rinsing with the hose (hence one hose for foamgun; one hose for rinsing)
-I do the initial passes (absolutely plural!) with the BHB and then switch to mitts after everything *appears* clean; each area gets washed numerous times, each one being so gentle that marring isn`t an issue (and/but it doesn`t get clean right away either)
-Mitts are filled with foamgun output and held shut at the cuff while being gently whisked across the vehicle; rinse/refill when all the shampoo mix has seeped out (at the latest)
While I`d *NEVER* wash without a foamgun, and credit its use with my vehicles remaining (virtually) marring-free for ages, I`ll readily admit that those who`ve watched me wash all say something like "No way am I doing that, I`d rather have swirlmarks".
