Renders are subject to cracking, degrading and debonding over time due to normal weathering, impact and freeze-thaw attack. We recommend that your render is still ok after the harsh winter of 2009/2010.
Hollow or debonded render can be found by tapping the render: if it makes a ‘hollow’ sound then it may be coming away from the wall and thus needs repairing.
The cement used for this type of job would be Ordinary Portland Castle Cement. The strength requirements of renders are widely varied and Ordinary Portland Castle Cement is designed to be adaptable in performance to accommodate the requirements of the application.
Cement is suitable for use in all types of renders. Care should be taken to ensure that the surface to be rendered is clean and free from dust. Mixes for successive coats should neither be stronger nor thicker than the previous coat. Each coat should be allowed to cure for several days before a subsequent coat is applied.
Ordinary Portland Castle Cement is a cement which enhances sustainability through the use of carefully selected recycled raw materials, reducing the carbon footprint of the cement.
What you will need for this job:
1. External bonding agent
2. Cement: sharp sand mix: Ordinary Portland Castle Cement
To repair a debonded render:
- Remove the hollow debonded render from the wall- correct preparation of the background surface is essential.
- The surface must provide a good key. It should be clean and sound; an external bonding agent is recommended.
- The patch repair should be of a similar mix proportions to the original render and would typically be a 1:4 or 1:5 (cement: sharp sand volume) mix.
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