you definetly need to prime new drywall with a good latex primer and 2 topcoats of either latex or oil top coat. Its really important to prime well or your top coat won't look good at all, and streaky. Lightly sand between coats and wipe dust off.

New drywall "drinks" primer. As primer is less costly than paint, I always do 2 coats of primer to make certain I have a uniform surface for the paint.

Oh good heavens! "Lightly sand between coats and wipe dust off" sounds like a heeeyuge undertaking. I'm not disputing if it needs to be done, just asking why? Very ignorant here..have never painted a room in my life, and right now I feel so overwhelmed by the 4 bedrooms, 4 baths, kitchen, halls, dining, living room, family room that ALL need to be painted in our new home.

My husband has knocked out the walls around the master closet, which was just your standard 2 sliding door type, and is going to frame and drywall it into a large walk-in type, so is he going to have to do this sanding/wipe off dust step for both the primer AND color?

Resurrecting this question to find out the answer:

You're supposed to sand (and dust!) the primer?!? AND sand (and dust!!!) the first coat?!? I'm not unwilling, but knowing "why" would maybe help me rally a bit.

You would only need to sand if the surface is rough. Usually if you use a good primer, the paper facing of the drywall does not raise that much to cause the surface to be rough. All it takes is a quick pole sanding...you hardly have to apply any pressure. People get all freaked out by hearing they have to sand...it's not a big deal, seriously. Get yourself a pole sander. You can buy them with the sanding pad attached already, or you can just buy the sanding head that screws onto any standard extension pole. Put some 150 grit on there and you are good to go. The first couple walls with the pole sander will be a bit tough going, but once you get that sheet of sandpaper broken in, you should be able to fly. Granted, some people have no coordination and can't pole sand....but just don't try to press too hard. Check your work with your hand as you go to get an idea how much pressure you need to apply. It shouldn't take much to get those walls perfectly smooth.

You should only dust if there is dust on the walls. Gravity usually takes care of the dust. It's minimal anyway when you are just sanding primer that is not that rough. The only time dust becomes a real issue is when you are sanding patching. The reason we may dust is because we want the topcoat to adhere to the primer. If you paint over a pile of dust, obviously that dust may impede that topcoat from sticking so later it will peel. You probably do not need to sand after the first coat. Generally, there is nothing that will make those walls rough again after your initial sanding unless you are painting with old paint that is all snotty or you are using a cheap roller cover that sheds all over. Then you would need to sand off the roller lint and snots. If your paint starts to get snotty, strain it. You can by strainers at the paint store or use some old nylons.

"...with old paint that is all snotty..."

Love that phrase. Describes well what that looks like.

By the way, thank you for all your patient hand-holding. You're right, people (okay, me) do freak out with the pole sanding thing. You're explanation makes it sound do-able. I'm still freaking out about all the dust everywhere, but it sounds like once we get the initial mess under control, this shouldn't be a big deal.

Why do you not recommend sanding the ceiling? Wouldn't the same principles apply?

Disregard the last sentence of my previous post. I mixed you up with someone else (christophern). Sorry.

Why do you not recommend sanding the ceiling?

If the ceiling is full of "snots" then by all means sand it. In my experience the ceiling is the last place most people look at( except painters)and rarely needs sanded.