Blocks and bricks made excellent decorating and design choices, but if you are ready to cover the old block wall and move on, they can present a hassle in terms of remodelling. Remodelling options such as paint or wallpaper will not stick to the uneven, textured surfaces of blocks and therefore limit your choices of what you can do to your wall. To create a flat surface that will accept your remodelling efforts, render the wall, which involves adding a layer of render (similar to plaster) that fills in gaps and creates a smooth surface for your future work.
Remove any lighting fixtures, outlet covers or any other removable objects from the wall. Mask off all door frames, windows and fixtures that you cannot remove with protective plastic sheeting held in place by masking tape. Lay plastic sheeting under your work area as well to protect the floor or ground.
Clean the wall with a push broom or scrub brush dipped in white spirit or a similar solvent cleaner. These cleaners remove dirt, dust, oil, wax and grease. You must remove all of these contaminants to ensure the render will bond to the block surface.
Rinse the wall with a hose to remove residual cleaning solution. Allow the wall to dry before continuing.
Set metal bead strips on all corners, around frames and outlets and along the bottom of the wall ½ inch above the ground. These metal strips will prevent the render from spreading around corners or dripping down the wall and creating a mess. Attach the strips to the wall with construction adhesive to ensure it holds. If necessary, apply masking tape to the strips to help them stay in place while the adhesive dries. Make sure the strips are firmly in place before continuing.
Mix your render material in a bucket with an electric stirrer. Follow specific product instructions regarding mixing ratios or create your own render mix using 4 parts sand, 1 part cement and 1 part water. Stir until the material has a creamy texture with no lumps.
Spread the render onto the wall surface with a flat trowel, working from the bottom up. The goal is to make the final surface completely flat and sit ½ to 1 inch above the highest point of the block work. Because of the natural divots and bumps in the surface, some areas will require more render than others.
Work the render across the entire wall surface with the trowel. Make sure you cover the bead strips as well. When you have completely covered the wall once, scrape a screed or a flat piece of wood across the surface to level off any bumps or bulges. Allow the first coat to thumb dry (the render does not indent when you set your thumb against it) before continuing.
Scrape a notched trowel or wall scraper horizontally across the surface, creating shallow (1/8- to ¼-inch) notches in the render. This will help the second coat of render bond to the first. Allow the render to finish setting completely before continuing.
Scrape your trowel horizontally across the rendered surface to remove the bumps you created with the scraping. This will leave only the notches on the surface.
Lightly mist the surface with clean water and apply your second coat of render, just like you did the first. Allow the second to set for 60 to 90 minutes before continuing.
Gently run the flat side of a plastic float over the surface in figure eight and circular motions to flatten any bumps and eliminate any trowel lines left from application.
If you have to cut your bead strips to fit around frames, use tin snips to cut a straight line through.