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 Natural Hydraulic Lime Harling Wet Dash

 

Introduction

The lime coating known as harling or wet dash is the most commonly applied external finish to be found on vernacular architecture in Ireland. The harling material is a combination of aggregates and lime, mixed into a slurry consistency and applied in a fluid state. Historically the harling was applied directly onto the masonry walls which had previously been evened out by pointing the wall flush and filling small holes with stone pinnings and mortar. Towards the end of the nineteenth century it became commonplace to apply one or two towelled undercoats to flatten the background before casting on the lime harling.

An extension of this practice became known as dry dashing or pebble dashing, where dry shingle is cast into a wet adhesive coat. However, in traditional harling the finish coat is applied directly to the masonry background.

Cottage

Preparation of the Masonry Background

Successful application of lime harling depends greatly on the amount of preparation that is carried out on the masonry background. External lime coatings are generally applied in relatively thin coats, therefore any masonry defects in the form of hollows or missing pointing must be corrected before the application of the harling coat. The correction of these defects should be carried out during masonry preparation and not rectified through coats of “dubbing out”. Areas of varying thickness are prone to shrinkage, carbonation and curing problems. Careful background preparation plays a vital part in the weather resistance capability of the wall.

Materials to be used in background preparation, should, wherever possible, be matched to the existing fabric. In doing so, the repair will be compatible and produce a similar performance pattern. Where previous remedial work has taken place with unsuitable materials, (i.e. dense cement mortars), these should be removed and repaired with matching mortars or stone.

The background must be free from dirt, grease and vegetation. These elements should be removed several weeks before repairs are underway. The removal of biological growths should be thoroughly carried out, as any remaining lichen, algae, etc, will grow back and attack the bonding between lime finishes and the background...