I have slump block walls that were covered in stucco at some point and now in places it's falling off. I know I need to power wash the wall and then use some kind of bonding agent so the new stucco will stick to the old wall but how do I apply the stucco? I feel like going from the skip trowel stucco look to the adobe look but that's a lot of walls to cover just to avoid learning how to do it the skip trowel way. Suggestions?
Preparation is all important for this kind of work.
You need to make sure you remove all of the loose stucco because if you don't it will affect the finish and durability of the repair. My approach would be to use a wide cold chisel and lump hammer to go beyond the loose areas into the area that's still sound a little way.
If you get a good stable surface then there shouldn't be a problem getting the stucco to stick.
One point to consider - if you call a professional they'll have all the right tools and the experience, whereas this will be a learning experience for you and to do a good job you might end up spending almost as much on the tools (though they can be hired).
The best thing you can do is remove all the stucco, then fasten a metal lath over the full area, then apply your base coat or base coats, then apply the finish coat.
You could just remove the loose stucco, clean the bare wall, then apply Weldbond (white glue) mixed with water at a 10 to 1 ratio: apply the bonding agent, let it dry, then reapply the bonding agent, then apply your coating.
But you might find that down the road, the work you have done is fine but other areas might just peel. Metal lath is the way to go, because it will never peel.