I bought a 2003 Kawasaki ATV that would get hot quickly, and found the radiator 80%+ completely full of the "cement" described when water and dust mix. It's not the end of the world, but is a huge PITA--and part of the deal with ATV's--water and dust mix on most recreational rides. I had to get access to the front and back of the screen, and began with compressed air from the back out. Might of got 1/3 opened, but still caked in corners and harder access areas. When air wouldn't budge anything else, it got the garden hose, and more came out, but on inspection--still very much obstructed. After water, compressed air got minimally more out.
Long story short, I decided to clean the radiator on the other ATV (nowhere near as bad) so I'd be forced to allow radiator#1 soak with a simple green detergent solution. I then alternated from one radiator to the next, allowing the detergent to work on one grill while I went at the other. Soak, rinse, blow out, repeat until water and air come through clean, and the radiator passes visual inspection. It took 4-5 applications, soaks, rinses, and blasts from the compressor before I got to open aluminum in all areas.
Compressed air #1, garden hose #2, garden sprayer & detergent #3. I'd get debris out using the water hose, but also got a surprising amount out with just the pressurized detergent from the sprayer. The narrow stream seemed to get into spaces the water hose would fill and protect with turbulence from the cascade of water coming down instead of going through.
I had never seen a radiator so bad--as far as coating the fins with a hydrophobic compound--I don't believe debris is homogenous enough to repel it with a charged or uncharged surface when its getting blasted into, over, and through the fins. Don't know you want to cover your heat exchanger with anything that could impede transfer either.
Do be careful--air and water can both damage a radiator with very little pressure.
Once you've opened it up, compressed air from behind should be all you need for PM.