After one day, fill the space between the guide strips with mortar 1:6 using a trowel. Make sure there is proper contact between the mortar and the underlying surface. The plaster should be slightly thicker than the guide strips. 7. Using a straight edge, screed the mortar to the same thickness as the strips. Use a float for the final smoothening as soon as a section has been plastered and levelled. 8. Plaster the entire wall the same day.