Stucco is a durable material but without a protective layer of paint, it will surely fail and cause problems...
In this article I want to dive a little bit into the different coats that are found in hard coat stucco systems to give you an idea of what to expect and try to tie in some expectations and comparisons that will make it clearer. This article is regarding 3 coat and 1 coat (2 coat) stucco systems, not EIFS.
Can Stucco Be Left Unpainted?
The short answer is... yes, stucco can be left unpainted for a short period of time or forever! Most stucco systems (not EIFS) use cement based products in their base coats and in some cases in the finish coat too (traditional finishes) which are proven to last long periods of time.
Just compare unpainted stucco to concrete, cinder blocks or mortar joints between bricks, as they are essentially using the same (base) materials and these tend to last a long time and are exceptionally resistant to the elements.
Vulnerable Parts Of The Stucco Process...
There are certain parts of the stucco process that are vulnerable and need some sort of protection and these are... the stucco paper (water resistive barrier) for the 3 coat systems and the foam that is used on the 1 coat (2 coat systems).
Those are the only parts of hard coat stucco systems that need to be covered up in a shorter amount of time (1-4 weeks is ideal). The sooner the better though!
The other coats can all be left forever if you choose to go that route or for longer periods of time because they consist of sand, cement, lime and water and are the same base materials that make up concrete (minus the gravel).
Do You Have A Finish Coat?
If you have a finish coat applied to the base coat(s) of your stucco and it is uncolored, then these too will also last just as long as if the stucco finish had color added to it, the only difference is that the color will be either white or a grayish-white, that's it!
This is true for stucco finishes that are an acrylic/synthetic and for traditional cement based finishes! Basically, all stucco finishes.
Stucco Base Coats:
Stucco base coats are made up of cement, sand, lime and water and the cement that is used is typically the Plastic cement because it has lime already added to it. The color is a dark gray when it is wet and it dries to a lighter gray, similar to cured concrete.
Typically a base coat is covered by a finish coat that is colored (color added) or painted but the base coat can be left alone and used as a finished product, in theory.
Stucco Finish Coats:
Stucco finish coats are typically white in color or a grayish-white color in their natural form so you can add color to them and tint the color. Even if no color was used, the natural white or gray-white would be just fine and would not need to be painted.