In an old building like this the walls suffer from presence of salt crystals. Salt is dissolved in rainwater and in groundwater and the brick walls have the characteristic to soak up the water because of capilair effects. After a while the water evaporates and salt crystals merge to the surcae of the bricks and morter and this results in a white vague shine on the walls. It is not bad but it does not look very nice so we removed it. Check out for yourselves!

white salt on the walls

and more salt....

scaffolding and just brush !

and the result...clean walls without salt.