How can a wall be "untexturized"?

There are different options. One of them is add a filler material to the texture, in such way that the surface is leveled and the finish is smoother, but this option can generate problems of adhesion due to the quantity of material.  Another option is to sand until leveling, which produces a large quantity of dust.  Whatever the method you choice, make sure to apply a sealer before apply the final finish to obtain a uniform finish. 

Which it is the most efficient method to paint surfaces with lime? 

Surfaces with lime have little or no binder and then tend to be chalky.  To paint a surface with lime, first clean the surface with a domestic cleaner to remove as much lime as you can. Then, rinse perfectly. Apply a primer or sealer that secures the adhesion on the chalky surface.  Subsequently, paint with at least two layers of the paint you choice for the final finish.

Is it possible to apply a water base paint over a surface that already has a solvent base paint? 

Yes it is possible.  There are two options to paint.  The first one is to wash the surface. Then sand the surface and withdraw the dust from the sanding process. Once the surface is sanded and cleaned, you can apply the water base paint over the surface that already has the solvent base paint.  This procedure is valid not only for surfaces in interior but also for surfaces in exteriors. Other option is to wash the surface, allow it to dry and apply a coat of primer. Once the primer has dried and hardener, apply the final finish paint. 

Is it possible to apply a water base paint over gloss, solvent base paint? Is it necessary a preparatory work in the surface to ensure good adhesion?

Yes, to both questions. But, in order to ensure a good adhesion to shin surfaces, it is necessary first to wash and, subsequently, to sand the surface. This process guarantees the new paint “grips” to the surface. Solvent base paints with gloss finish tend to be chalky, especially when the paint has a lot of time since it is applied.  That’s why it is necessary to clean the surface before applying the finish paint ensuring its adhesion and long-term durability. 

Why it is necessary to use a primer instead of applying only two coats of final finish paint?

Primer has a lot of benefits, because it helps to generate a uniform surface and promotes a good adhesion of the final finish paint. Primer is also useful to seal porous surfaces, improving the yielding and stain resistance of the paint. The use of printer, in most of the cases, depends on the characteristics of the surface to paint. 

Is it possible to apply solvent base paints directly over aluminum metal?

Solvent base paint should not be applied directly on aluminum because, as happens in galvanized surfaces, the resin of the paint reacts with the metal, generating potential flaking. Wash Primer type product must be applied previous to the application of solvent base paints over aluminum metal. 

What causes small cracks on a recently painted wall? 

The problem of cracks is called commonly “alligatoring”.  The most common cause of alligatoring is the application of a paint film with relative high thickness. The surface of the paint film dries first, while the rest of the film requires more time to dry.  Once all the paint film has already dried, this one contracts and shrinks. This problem can be prevented applying the paint at the recommended film thickness and dilution rate established by the manufacturer. Conversely, alligatoring phenomenon can be generated, in smaller proportion, by the application of the paint in a surface contaminated by greasy materials, silicone, greasy bodies, etc., which can be prevented by prior surface cleaning before painting. 

Which it is the best method to clean a new galvanized surface before it is painted?

The new galvanized surface must be cleaned with a chemical solvent to remove contaminants and greasy materials applied by the manufacturer (to prevent the oxidation of the zinc in the galvanizing process). Complement the cleaning with water based degreasing agent, applied with a sponge or piece of cloth.  Once the cleaning process is carried out, rinse perfectly the surface and let it to dry completely before painting.