Render is a mix of cement, lime and sand applied to external walls either to make them more waterproof or to cover up less attractive materials. If cracks appear in the render of your house (which can happen during the normal movement of your house) rainwater is allowed behind the render, which can cause large patches of the surface to crumble away. Before undertaking any repairs to render, you should treat the exposed bricks with a PVA adhesive.
Applying a Scratch coat
Once you have mixed your mortar place some on a hawk and hold this next to the wall. Use a float to push the mortar into the damaged area, repeating until the hole is filled very slightly below the surface of the wall. Leave the mortar to harden slightly and then scratch a crisscross pattern into the render to provide a key for the finishing coat.
Applying a Finishing coat
Choose a finishing coat that closely matches the rest of the wall and then spread it over the now hardened render until it is slightly proud of the surrounding area. While it is still wet use a straight piece of wood, dragged across the surface, to remove any surplus mortar. Leave this for about an hour, dampen and smooth off with a float.
Painting Exterior Render
Applying a good masonry paint to rendered surfaces will not only look better but also increase its resistance to water. Exterior emulsion paints provide only a decorative finish and should not be used as waterproofing.
