Patching and Plastering - Knock down finish

I found some threads indicating that a knock down finish is applied by spraying. My daughter is renovating a room and wants that finish on the walls.

She's never done any DW taping before, I helped her hang it but won't be around when she tapes/muds the joints. I'm sure she'll have some joints that won't be perfect. Right now her plan is to do the taping herself and hire some one to spray the knock down finish.

I have a couple of questions. Can the finish be applied over regular drywall or is blueboard required? How good is a knock down finish at hiding blemishes in the DW joints?

It will depend on what and where she's applying the drywall knockdown texture. What exactly is she looking for--an easy way to mud or a decorative finish? Knockdown textures aren't always sprayed, and many decorative knockdowns are hand-applied using different methods and tools. If she is learning to finish, I recommend the magic trowel--even a novice can mud seams, get near perfect skim coats and/or do a knock down with it.

Can the finish be applied over regular drywall or is blueboard required? How good is a knock down finish at hiding blemishes in the DW joints?

Knock down like most any texture can be applied over regular drywall. Blueboard is only used when you want an veneer plaster finish.

The heavier the texture, the better it will hide imperfections. It won't "fix" a bad finish job.

Drywall finishing isn't rocket science - it may take extra mud applications and extra sanding but most anyone is capable of doing a decent job.