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 External Natural Hydraulic Lime Render


Preparation of the Wall Surface

The successful application, bonding and correct hardening of hydraulic lime mortars, requires that the background should be clean, free from vegetation, free of containments and reasonably dry throughout the wall mass. The wall should be structurally sound and the masonry and bedding mortars in good condition.

Where natural weathering or incomplete repair works have previously been carried out, new repair work will be required to correct these defects. In masonry the natural weathering process can result in the loss of small stones, known as pinnings, which are traditionally placed into wide bed joints between larger stones, where these are missing their replacement should be carried out with any general repointing work which needs to be undertaken. (See repointing).

Wallfield House

Where walls are covered in vegetation, lichen or moss, these should be removed, by use of cutting stems, treatment with biocides and eventual cleaning down with brushes, any remaining biological growth can retain water and may in time grow back through the new lime coatings.

The application of various coats of hydraulic lime should not be seen as remedial repair works to the masonry background, the replacement of loose or defective mortar, replacing missing stone pinnings, repairing damaged brickwork or stonework are distinct separate operations and there eventual outcome should be to present a reasonably flat and even surface, which is structurally sound and clean ready for the rendering application.

Suction Control and Bonding

Before the application of any new lime coatings it is vitally important to check the degree of suction within the background. Poor or excessive suction can result in a weak bonding with the substrate caused by rapid de-maturing of the newly applied render. This will result in a weak and powdery interface which could lead to later failure and separation.

In situations where suction needs to be controlled, wetting down will be required. On dense blocks or near impervious masonry, simply dampening the surface with a mist spray may be all that is required...