How To Do Lime Rendering?

Lime rendering is a time-honoured technique that has been used for centuries to protect and beautify the exterior walls of buildings. Whether you’re restoring a historic structure or simply want to add a touch of timeless elegance to your home, lime rendering can be a fantastic choice. In this guide, we’ll walk you through the essential steps and techniques involved in lime rendering.

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Preparation of the Wall Surface

Before you start to apply lime render, it’s crucial to prepare the wall surface properly. The success of your lime rendering project depends on the condition of the underlying wall. Here are some key considerations:

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Clean and Contaminant-Free: Ensure that the wall surface is clean and free from vegetation, contaminants, and loose debris. Remove any existing paint or coatings. 

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Structural Soundness: The wall should be structurally sound, with no significant cracks or damage. Any missing or damaged masonry should be repaired before rendering.

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Suction Control: Check the degree of suction in the background. Poor or excessive suction can result in weak bonding with the substrate. Dampen the surface as needed to achieve the right level of suction.

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Salt Contamination: If you’re working on masonry that’s salt-contaminated, allow it to dry fully before rendering. Excessive salt may require specialised poulticing techniques.

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Techniques of Hydraulic Lime Plastering

Lime plastering is typically applied in three coats, but you may encounter two-coat or single-coat work in older structures. Here’s a breakdown of the three-coat method.

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First Coat (Scratch Coat)

Apply a 10mm-thick scratch coat using a trowel. Key or scratch the surface to create a bond for the following coats. Allow this coat to firm up and then let it dry for at least 72 hours. Fill any shrinkage cracks that may appear. 

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Second Coat (Floating Coats)

The floating coat is straightened to create a flat and even surface. Scour the surface with a timber or polyurethane float to complacent the plaster and counteract shrinkage. Repeat this process at least twice and fill any small holes. Allow the coat to dry and harden for 72 hours.

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Third Coat (Setting Coat)

Dampen the floating coat and apply the setting coat in two layers with a trowel. This coat can be left with a textured finish or polished smooth with a steel trowel.

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Mix Guide

The choice of lime and sand mic is crucial for achieving the desired finish and performance. Here’s a general mix guide:

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Backing Coats (1st and 2nd) - Mix 1 part NHL2 or NHL3.5 with 2.5 parts sharp-washed sand. It’s recommended to include fibre or hair in these coats for added strength.

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Finish Coat - Mix 1 part NHL2 or NHL3.5 with 2.5 parts sharp-washed sand. It’s not necessary to add fibre or hair in the finish coat.

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Lime rendering is a craft that requires patience and attention to detail. By following these steps and techniques, you can achieve a beautiful and durable lime-rendered finish that stands the test of time. Remember that each project may have unique requirements, so don’t hesitate to seek specialist advice when needed. With practice and dedication, you can master the art of lime rendering and transform your walls into works of art that last for generations.

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