The leveling coat creates the form of the wall, with variations in the plane being defined in the UBC and the International Code docs as being anywhere from 1/4″ in 5 feet to 1/8″ in 10 feet with a 10′ rod measured in any direction. Pleasing to the eye always works, so lumps and major voids should be avoided. It should be flat. It should be hard, and prepared or floated so as to be able to accept the finish coat.
Plaster Rods and darbys and slickers are used to create a flat wall, with slickers and darbys closing the pores of the material and rods opening the material up. Closing the pores of the material keeps moisture in the panel, opening up the pores allows air to start the process of setting the panel. All this before a plasterer with a float, either wood shingle, hard rubber or green foam float densifies and knocks clinkers off the wall.
The other way of creating a really flat wall is to rod the wall. Which is to let it get firm, then skim a leveling coat of material like drybond or stucco finish over the firm brown coat. This process really flattens the minor variations in the wall and seals the open pores of the cement plaster so the wall gets very hard. With the drybond material it get incredibly hard and is a perfect base for an Acrylic finish.
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