Cracks and Plaster
Bare walls are not very smooth. Cracks will be found here and there as a natural occurrence from the drying of cement. Regardless how good the concrete was packed and laid, the final result will be riddled with small gaps. Unless those imperfections are patched up with plaster, they will be as visible as they are even with a layer of paint.
Blue is not going to be the blue described in the paint book if only one layer will be applied. There needs to be a primer which will negate the colour of concrete and plaster from affecting the paint. This is usually colour white and makes the wall a big canvass.
The Paint Itself
After the wall has been turned into a conducive painting platform, the layers of colour will then be placed, though, it does not get any simpler despite the preparations. There are rules for proper execution that will ensure the best output. This includes following a single stroke and laying a thin layer one after the other. It is a time consuming process and not everybody is going to be up for the task.
A painter’s job is nowhere easy. It is a long and tedious process that requires a lot of skill and experience. Unless quality is not an issue, then a person can paint the wall himself. Though, with the likely output, the wall would be better off without the paint.