Ahha,, know where you're coming from now Rusty. He's wet dashing. Ok,, you don't need waterproofer in the scratch coat for that. When it comes to the actual dashing, the wall is given a "light" dampen down, and then a thin coat of cement render is troweled onto the the scratch coat. This is the "wet" base for the actual wet dash to be cast onto. Wet dash is a slurry mix made up of sand, cement, lime, and small aggregate chips. It's similar to a small concrete. It is thrown onto the thin wet render coat, that is applied prior to dashing, with a harling/casting trowel. It is a harder job to do than dry dash, and if done incorrectly, (whipping), uneven application/spreading,, it will show up in the finished job.
For your information, waterproofer,, (a liquid render additive, mostly used in dry dash scratch coat, along with other cement finishes), holds the water in the render for longer, to allow the chips to be cast onto the wet rendered surface. If the surface dries out too quickly, the roughcast chips will bounce off of the render urface, rather than penetrate into the render itself.
With wet dash, you want/need suction (so no waterproofer) that way, the wet dash can be applied and draw in/absorb into the wall quicker, rather than staying overwet and becoming too heavy, and then slumping downwards/ splitting. Can be a tricky job to be honest, and not the most common of finishes nowadays, especially on new builds etc,,,, around here anyway,,, but keep us posted how you get on tomorrow.
