Is Rendering a Good Solution for Weathering and Rainwater Penetration

An aspect that is often discussed in terms of an advantage ofrendering a home is the enhanced weathering it delivers. However, there is the question of whether rendering provides waterproofing and if not how to make rendering waterproof to ensure the exterior of the house keeps looking dry and clean during wet weather.  

Exterior construction material whether it isrender(made of cement or lime) or brick, is naturally porous, this means that it has water-absorbing qualities rather than water-repelling qualities. Because you plan to render the exterior of your wall at a considerable cost it makes sense to ensure that it provides the important and additional benefit of weatherproofing/waterproofing apart from improving the look and feel of the home. The level of weatherproofing or waterproofing delivered by rendering depends on the formulation used and how it is used on the exterior surface. 

Rendering is also used as a quick fix to save walls from dampness. While rendering does prevent dampness from water absorbed through exposed brickwork or stonework it is important to assess if the dampness is caused by damaged guttering and leaking roofs, in which case the cause of the issue should be addressed first. The waterproofing that rendering provides is via a non-penetrable cover of the exterior walls where the render acts like a shield. It doesn’t provide a guard against other areas of the house through which water can permeate. Whether you are repairing your render or applying it for the first time, you need to add a layer of waterproof coating over the render to ensure the surface repels water.

The case for render to be waterproof: moisture is the number one reason for the structural deterioration in houses. Moisture also leaves unsightly dark patches on wet walls, mould, peeling paint and crumbling exteriors. Water can over time find its way inside to damage interior walls as well. Penetrating dampness is another problem. Water is absorbed by the rendering during heavy rains and will continue to make its way to damage interior walls. Moisture absorption through exterior walls hurtsboth the strength and structure of the wall as well as the appearance which should give homeowners enough reason to ensure the render that is chosen is water resistant. 

Silicone renders: there are a variety of renders in the market to choose from. The waterproofing/weatherproofing ability of the render depends on the mix of compounds in the render. Among them, silicone renders are on top of the list for waterproofing ability. Silicone renders are advanced renders that have silicone as a key ingredient to provide a highly water-resistant rendering material that also has high breathability. Renders that are lower down the scale on waterproofing ability have less breathability which traps the dampness preventing it from escaping and causing cracks in the render. The cons of applying a silicone render to your exterior are that it tends to discolour over time if not cleaned periodically and its high cost.

Anne Allison
the authorAnne Allison

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