If you want smooth then it has to be really, really smooth. And really, really perfect. "Pretty smooth" will show every imperfection. I'd put at least orange peel or sand texturing on it before the primer. I just put knockdown in one room and it's a bit strong for my taste.

We had popcorn ceilings removed from our 1500 square foot house in 1991 when we bought it and before we moved in. It was a very messy job, but it was done right. We have smooth ceilings and, with the exception just a few inconspicuous areas, no patching had to be done.

If your popcorn removal left a smooth celing that's got a lot of cracks and bumps, you will need to patch it up. It can be done DIY, but it's very hard a tedious. The alternative is to hire a professional plasterer, which can be expensive. A less expensive alternative is to hire a handyman who can do a reasonably good job of it, it you're lucky enough to find such a person.

One consideration is how visible are the imperfections. That depends to some extent on the shininess of the paint. Flat paint will show imperfections a lot less than shiny paint. But for a bathroom, you'll probably want semi-gloss.

What is knockdown? A guy in the paint dept showed me 2 products, a sand texture paint and popcorn texture paint. He said they can both be colored to whatever I want. He put some on a stick and the popcorn wasn't as thick as the stuff on my ceiling, it did look more like orange peel. I wonder if anyone has used these products.

We are still working on removing popcorn from our ceiling and there is no way that I will put another texture on. If you're getting rid of it why replace with another type of texture? That was the argument I got when I came here to ask and I thank the person who asked me that!

Fortunately, I do have someone who makes my ceiling so smooth, it's almost as good as a baby's :-)

Mari

..and I'm hoping all of you had the ceilings tested for asbestos before you started your projects...

Here is a link that might be useful: Proper removal