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Weber - Saint-Gobain

Rendering inappropriate surfaces

Render finishes are often the final and most important element in the building process as they define the overall aesthetics of the structure. All too often they are considered as a cover-up for other construction bad practice and poor alignment. Sometimes renders are required to be applied over inappropriate surfaces.

Problem

1. Painted or coated substrates

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Painted or coated substrates offer low suction and often poor key for render finishes. Additionally, the bond strength of the coating to the substrate is usually too low to carry the weight of a render coat.

2. Substrates out of plane

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Construction tolerances or dimensional accuracy of blockwork and concrete is often at odds with the accuracy needed for good rendering. Steps in the surface or excessively thick areas of render can give rise to potential cracking or shading problems.

3. Dissimilar substrate materials

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Existing cracking or the potential for differential movement arising from dissimilar substrate materials can transfer stress into a new render, resulting in cracking.

4. Weak substrates

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Renders applied to substrates that are too weak or to those with weak surfaces are likely to fail along the plane of the interface as the surface of the substrate itself fails.

Solution

Treat surface and finish with EWI system

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A detailed assessment of the condition and flatness of the substrate surface must be made by the specifier. The assessment should consider whether the surface will allow for direct application of render or if additional mechanically‑fixed render carriers are required. Sometimes the surface will require dubbing out (making level) before rendering can proceed.

Solution with the following Weber products

Solution 1

webertherm FT - FrameTec System

An extruded aluminium spanning rail to provide a cavity when using External Wall Insulation with single skin or frame construction

webertherm XM - Multi Layer System

Our traditional multi-layer render system which incorporates an extensive range of versatile and attractive finishes.

webertherm XP - XPress System

Our unique XPress system incorporating a through-coloured render which can be applied by pump for speed and simplicity.

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