1. Gear up
Prepare your tools and materials. You’ll need a dust mask, safety glasses, and protective gloves. You obviously need sand and cement (or a pre-mix) to make the mortar. You’ll also need a mixing drill, a few buckets, and a spirit level, a long screed, a plastering hawk and a trowel.
2. Prepare the surface
Use a wire brush or industrial broom to remove any excess dust and scrap off any extra mortar coming out from the concrete blocks installation. Lightly spray the surface with water to help adhesion. As a guide to the plastering thickness, you can nail small pieces of wood at different areas of the wall.
3. Load the hawk with some mortar
Use the trowel to put a sufficient portion of mortar to work with and mix it to ensure you have a good consistency.
4. Apply the plaster (mortar) to the wall
Use the trowel to apply an even layer of plaster, starting from a top corner, going to the bottom. Work with a few blocks at a time, and try to maintain an even spread until you have covered the entire wall.
5. Screed the plastered surface
Mortar sets quickly, so once it is dry enough, apply pressure with the metal screed to achieve a smooth surface. Start from one side of the wall, keep even pressure, and work your way to the end of the wall. You’ll flatten the surface and get rid of any excess mortar.
6. Check levels and straighten the wall.
Check if the mortar is straight. A deviation of about 3 mm for every 2 meters is an accepted tolerance. Use the spirit level to remove any excess plaster if the wall level is not flat, until you achieve the desired level. Run the screed again to get a smooth surface.
7. Use the trowel for touch ups and corners.
Patch any areas that were missed using the screed, especially the corners of the wall and any areas were some irregularities in the wall existed. Smoothen the edges of the wall.