Rendering a wall is the act of applying a layer of material such a sand & cement (lime can also be used) to a brick or masonry wall to render it smooth. The wall may then be painted if desired.
Things you’ll need: Wire brush, Plastic or wooden float, Wire scratcher, Steel trowel, Wooden battens, Straightedge, Spray bottle
Preparation is the key: Make sure your wall to be rendered is really clean and etched so you get maximum keying and suction between render and masonry. Chip away any old render or loose mortar. Brush off any organic growth or material. If the bricks have a smooth surface texture, chip away at the front of the bricks to create a key for the render.
Fix vertical battens to the wall about 10mm thick, and about every 900mm, packing them out where necessary to take up undulations in the wall.
When fixing the first batten to a corner or the wall, make sure it is straight and upright even if the wall is not. Each space between these screeding battens will be filled separately. This method is the easiest way to keep the render flat and even. Before you start, spray the wall lightly to make damp…this will help to achieve good suction.
Render Mix: 1 part cement….6 parts clean sharp sand (tip..try and use plastering sand)
Add the correct amount of clean water to get the best trowelable mix, too wet and it will slump and too dry and you won’t be able to apply it (it will crumble). Also add a waterproofing plasticizer to the mix..this helps to stop water penetrating the finished render and improves flexibility
Application: Starting at the top, load the hawk and then pick up the mortar on the trowel. Pushing upwards in a slight arc and keeping a firm pressure, build up the render on the wall between the battens. Level this undercoat off by “see-sawing” the straightedge upwards along the battens. When each bay is filled scratch the surface using a wire scratcher. Allow to dry before removing the battens and filling with the same mortar mix.
The render coat can be built of up to two or three layers, first a rough keying scratch coat 5-10mm, a second body coat of 10-15mm with scratching and then a final coat 5-8mm (the thickness can vary depending on the state of the wall..i.e. a “straight” or “plumb” wall should only require the two coat system.
In hot conditions outside you may need to control excessive drying, shrinkage and cracking by keeping the render moist with a sprayer (though not dripping wet)
Finishing: To achieve a matt slightly rough finish, rub over with a plastic or wood float, or a steel float for a smooth paintable finish.