I've written an extensive article on architectural paint but all has been wiped off with the recent attack on nairaland and I have to open another moniker and start another thread.
I'm going to talk about different types of paints and properties and also post pictures of some projects I've been privileged to supplied by some nairalanders here. Its a pity that most of the comments are gone.

Painting is the last finishing on a building and when nice complementary colours are used, it adds beauty to the building.
However, painting has gone beyond just beautifying of a building, its also a protective coating that serves as the first line of defense against weathering of the building.

There are various types of paints used in building like ; emulsion, textured emulsion, matte emulsion, satin emulsion, eggshell, flex coat (patterned plaster), marble trowel, stucco paint, mineral silicate paint , gloss oil paint and so on.

Emulsion paint is the most used paint but for some reason, we have various grades of the emulsion paint in nigeria market.
The different grades are invariably dependent on the price.
We have some regular bulk produced low end paints that goes for N2800 here in lagos, standard grades that go for N5000-N6000 and premium grades that go for N9000 and above.
The prices are largely dependent on the amount of opacifying pigment and binder.
These determine how opaque the paint would be, how many coats of paint needed to cover the wall and how durable the paint would stay on the substrates. The remaining materials in the paint are mostly regular for all grades of paint.

The low end paint is ideal for interior painting where it won't be subjected to rain and sunlight so far its not the type that rubs off and stain when touched.
If this type of paint is used outside, it won't last for more than a couple years if not months during raining season depending on the type of binder used or how low the binder is.

The disadvantage of this type of paint is that once it fails, it becomes powdery and crumbly and subsequent paint applied would be on top of the loose surface instead of a firm and stable surface. And no matter how good the new paint is, it would be sitting ontop of an unstable surface and can easily come off.

The standard grade paint is ideal for interior and exterior and can last for 5 to 10 years before needing re-coating.
If one is particular about appearance of the building, low grade paint would have been applied more than twice that period not including the labour for painting.

The premium grades are basically matte or eggshell paint.
They are also durable and can last upwards of 10 years with the benefit of covering more that twice of the areas standard paints can cover due to their very high opacity.

Same thing goes for the low grade paint too. The regular grade is much more opaque and covers more area so.
So basically, its more like buying diluted or more concentrated paint. Its not about how thick a paint is, those are the fillers that gives the paint body and have nothing to do with opacity. Its all dependent on the base titanium dioxide pigment used before other colourants are added.

Therefore, its advisable to use standard or premium grade paints to get a lasting paint and save cost on the long term.
The quantity of paints needed also reduces with the quality of paint.