How to level sloped concrete ceiling, and is it worth it?

Question

I want to remove popcorn ceiling in a 7' by 14' room and turn it into a smooth ceiling. I have just built this room. The walls are not yet painted, so now is a good time to do the ceiling.

I know how to remove popcorn by spraying it wet and scraping.

The question is what to do after the ceiling has been scraped. It is poured concrete, with some visible depressions, hard to say how deep, probably 1/2". The ceiling also has a tilt to it. It is most pronounced along the shorter 7' wall with about 2" drop.

Now if I were to go for a level ceiling, that would require a lot of compound to fill that slope. Just to estimate (assuming the slope does not run the entire length of 14' but only half), 7' x 7' x 1" = 49 sq ft. x 1" = 4 cubic ft = 30 gallons of mud. That is a sizable amount of mud to buy, mix, and apply.

Is it actually worth being a perfectionist here? Can I get away with simply smoothing out the ceiling, hiding most noticeable blemishes and leaving the slope as-is?

Either way, what compound should I use, and what is the recommended way of applying and smoothing it?

Edit: Thank you for your answers. Both provide great info, I just wish I could mark both as "the answer". Quick update: scraped popcorn last night. It was quite easy (not nearly as difficult as some DIY articles lead me to believe). After hearing opinions here, definitely not going to level the ceiling. I bought this type of compound for the job.

I have an assortment of drywall knives. Which knife should I use? What primer should I use? Once sanded smooth, should I paint the ceiling -- if so, what type of paint should I use?

Answer 1

If you want it level, cut furring strips and put up drywall.

If the precise shape of the ceiling is going to bother you, that might be worth the agony and is a heck of a lot easier than trying to get that much mud onto the ceiling, much less on the ceiling and actually level. I wouldn't bother with it, personally. The slight angle would not offend my sensibilities, and is also better acoustically than a dead-flat ceiling.

For smooth, drywall compound or actual plaster will do. I'd lean towards plaster for concrete, but I'm not sure there's anything to my bias, there, other than my bias. Grab a big ol' knife (or trowel) and go. If using mud, probably the 90-minute setting (aka "hot mix") compound, unless someone else has a better reason than my bias in support of my bias.

Then again, USG (and probably others) has a compound specifically for concrete.

COVER COAT® Compound is a premium mixture ideally used for filling and smoothing above-grade, monolithic interior concrete ceilings and columns, embedding paper drywall tape or acting as the first fill coat on bead, trim and fasteners. The compound dries white for a quick, easy finish.

Further reading:

Gypsum Plaster over concrete and Portland cement "plaster" (stucco) over concrete

Answer 2

I don't think you should worry about level, as long as the surface is relatively flat. After you get all the popcorn completely off, you can use a setting type joint compound to fill any gaps. This is the compound that is sold as powder in bags. Get the 'easy sand' compound, available in big box stores so you can sand away imperfections. You can apply to impressions and other imperfections with a drywall knife. Anticipate that at least three coats will be needed.

For a perfect finish:

1. Sand away any compound that isn't perfectly feather-edged to the ceiling. A flashlight and a pair of stilts would help alot.
2. Prime the ceiling.
3. Then apply a skim coat of compound with a 14" flat trowel (not a drywall trowel).
4. Lightly sand and follow with primer again.

It's best to prime before the skim coat, because without it, the ceiling with take water away from the compound unevenly, making it difficult to get a smooth finish.