I was thinking recently about a product I was pitched by an Ace Hardware PR person last year–ceiling paint that changed color (from blue when wet to white when dry) to make coverage easier/drying more obvious. But this got me thinking–why is there a specific ceiling paint in the first place? Why is white wall paint not good enough?
Everyone I’ve asked has told me ceiling paint’s thicker. Ya know, so you won’t drip it on your head while you’re painting. Seems reasonable.
-Lil
Also, it splatters less and dries more quickly. The cost is durability – a coat of ceiling paint is easier to damage than wall paint. Happily, the kids don’t color on the ceiling and the annoying contractor/brother-in-law/dog doesn’t get his grubby paws all over it so it doesn’t need to be cleaned as often.
It dries too quickly in my opinion. I always get steaks and lap marks in ceiling paint, unless I use something like Flotrol to slow down the drying. I never have that problem on walls even without the additive.
If you are painting over a textured ceiling, you need to be aware thart some paints soften the plaster and the gravity can cause chunks to fall. I was warned about that by a professional house painter, but that’s all I can tell you.
As long as I’ve been doing remodeling work, I’ve used MAB flat white latex paint for ceilings unless the customer has a color/gloss preference. Even with an 18" roller, spatter is almost negligible.
Hey! I work at Ace Hardware! All of what you have said so far is true but there is one main reason for a special ceiling paint. Ceiling paint has a flatter finish than even a normal flat latex paint. This helps hide and imperfections in the ceiling. In general, the higher the gloss the more imperfections that are shown. Ace Hardware’s Ceiling Magic paint has a flat finish and a light blue color when wet to make sure you have hit all the spots.
And by the way, yes it works!
From a rheological pov, ceiling paint may have a higher concentration of **thixotropic ** additive.
Thixotropic means that when you stir the stuff it thins out and over time sets back into a gel. When the paint is applied with a roller it is exposed to a shear strain that temporarily breaks intermolecular bonds within the structure of the paint. With time these reform and the paint viscosity increases.
So the paint levels nicely on the ceiling before resetting into a gel. Also reduces splatter during application because the paint thins out.
Most paints are thixotropic to prevent separation of the components on standing (in the can) while allowing easy stirring and application.
This is why I love the Straight Dope! 
Um, it sticks real good, and dang if that dullness don’t hide the imperfeckshuns!
Gots to like dat there color change, cause when yer sniffin’ paint all day, ain’t no one gonna look up real good to see if you covered all that ceiling.
Serious question here. If you need the blue to see if you missed a spot, WHY on earth would you be painting the ceiling?
Years ago, GLIDDEN marketed a ceiling paint that was actually a powder-it would adhere to a roller, and stick quite wellto the ceiling. haven’t seen it in years…anybody know what happened to it?
I’ve found that when painting a ceiling it’s more difficult to see where you’ve already painted than when painting the walls. If you’re question is more along the lines of why someone who needs that sort of visual assistance doesn’t just hire a professional; the answer to that would be money. Pro painters are not cheap.
I think the question was “If the new paint looks that much like the old, then the old must look fine, so just leave that.” But it’s not that simple, because sometimes a surface as a whole can show imperfections, but when you zoom in it all looks the same.
This seems rather obvious, doesn’t it? But in practice it can be harder to catch miss spots than you’d suspect. And if color differences are subtle, it might be something that you don’t notice when painting but is obvious when the light is different. After you’re already put away the ladder and dropcloths. Argh!
When the sheen is gone, and the paint has cured, THEN you notice the subtle differences. Sublte is STILL annoying, lynxie.
Thanks, people. Shade got my question. (Sorry, typing is hard for me so detail gets lost.)
Makes a little more sense, now.