Rendering is popular because of its durability and its uniquely textured appearance, however, it is not immune to damage and can crack quite easily if, for example, the house foundation sinks unevenly or new framing members shift and shrink as they dry out.
As soon as you notice a crack in your rendering, however small, you should make a point of getting it fixed as quickly as possible. The smallest of cracks in the render will allow water to seep into the underlying structure and will eventually cause damage.
Overtime the build up of water and the cyclical temperature changes will cause those small cracks to turn into major problems which are both costly and difficult to fix.
It is ideal if you can patch large cracks and gaps in a rendered surface using the same rendering mix that was used on the walls initially. However, where this is not possible, you should use a rendering patching compound and refer to the package instructions for specific information for that product.
In the case of small cracks, they can be filled with all-acrylic or siliconized-acrylic sealants. If you spot large cracks but don't have time to make a thorough repair, at least seal the openings with a bead of silicone caulk to temporarily keep out water until you can get around to making permanent repairs. The caulk can be peeled away easily when you do.
It can be difficult to match the colour of rendering and so, for a surface that requires many patches, it may be far easier to just cover the whole surface, once patched, with a cement-based paint or acrylic exterior paint. You should ensure though that you let the rendering patches cure for at least 30 days before doing this.
When you come to paint the walls you should dampen it prior to applying the paint. Cement-based paint will need a primer coat to prevent blotches but this will not be necessary if you chose to use an acrylic paint.
Tools for the job
A poor workman may blame his tools but without the right tools a good workman may find themselves doing the same thing.
As is the same with any DIY job, you are far more likely to achieve good results if you do the job properly, with the right equipment. You are also far less likely to cause yourself an injury!
To repair the rendering on your external wall you will need the following:
• Work gloves
• Safety goggles (always wear goggles when breaking stone or cutting brick)
• Cold chisel
• Short-handled sledgehammer
• Premixed render or render patching compound
• A hawk for moving the mix to the job (you can buy one or make one by screwing a short length of dowel or broom handle to a square of plywood)
• Mason’s trowel
• Straight-edged board
Depending on the job, you may also need the following equipment:
• Ladder (depending on the height of the job, of course)
• Metal shears (depending on whether the render is reinforced with wiring)
• Steel mesh (depending on whether the render is reinforced with wiring)
• Galvanised Nails (depending on whether the render is reinforced with wiring)
• Finishing tool (if you wish to duplicate the texture of the surrounding render)
Getting on with the job
Step one: Removing the damaged render
Once you have donned your safety goggles and work gloves – and if necessary positioned your ladder securely on a level surface – you are ready to begin removing all of the damaged render with the cold chisel and the short-handled sledge hammer.
It is a simple case of chipping away at all of the damaged area until all of the weak/damaged render is removed.
Step two: Repairing any steel mesh reinforcement
It is likely that any steel mesh reinforcement will be damaged if the render on top is damaged. If this is the case then it must be repaired, this is a relatively simple process which involves cutting a new piece of mesh and attaching it to the wall with the galvanised nails.
Step three: Filling the hole
Now that all of the prep work is done it is time to apply your new render. Mix more than enough render or render patching compound to fill the hole and trowel it onto the mesh, pushing the render into the mesh. Use a hawk to hold your supply of render as you fill the hole, the patch should be thicker than the adjacent render.
Step four: Getting the right finish
Use the surrounding wall as a level guide, and smooth the patch surface by sliding a straight-edged board back and forth, achieving a level surface by drawing the straight edge across the wet render mix.
While render is still wet, try to duplicate the texture of the surrounding render by passing over the wet surface with a "finishing tool" such as a trowel, a board or whatever is appropriate for the particular effect.
Alternatively, if you don't want to do the job yourself, you can get no obligation quotes from up to 3 interested tradesmen from Rated People.