Old, strongly rusty steel bridge to be repainted. Please list the necessary steps in this regard
These steps are as follows::
1) grinding the steel structure with blast furnace slag;
2) painting with epoxy primer paint, with the addition of zinc dust;
3) covering paint with polyurethane varnish;
4) second painting covering with polyurethane varnish.

Already painted steel frames are to receive a new coating. The old coating turned out to be alkyd varnish. The plaster stained from rust at the joints of the door frame with plaster.
Such effects can be avoided in the future, by painting the door frames with glossy varnish. Please list the activities to be performed and justify them These activities consist in:
1) removing the plaster along the door frame, stained by rust;
2) washing off the old coating with a lye remover, and then rinse thoroughly with water;
3) cleaning the door frame from rust (also in previously plastered places) to obtain adequate cleanliness and thorough sanding of places previously covered with rust;
4) priming all accessible steel surfaces with lead-free alkyd anti-corrosion paint;
5) painting the door frame with alkyd varnish;
6) plastering the wall at the junction with the door frame;
7) painting with base alkyd varnish;
8) can be painted with a glossy alkyd lacquer.

Justification:
As stated, that approx. 35% the surface of the old coating has come off, this coating would be difficult to repair and must be removed completely. Because the old coating is made of alkyd varnishes, a lye remover is well suited for its removal. Alkyd varnishes are saponified by alkalis, and the saponification products can be washed off with water.
The rust stained the plaster, because the door frames were plastered without prior anti-corrosion protection. These steel surfaces need to be uncovered and primed. After rust removal and cleaning, a new anti-corrosion coating should be applied. Because the surface covered with alkyd varnish is prettier than the surface covered with dispersion varnish, alkyd products are preferable for this coating.