Walling

Walling covers the use of Portland Stone on all walls except cladding (see external cladding section). Load bearing walling was the traditional building method of Portland Stone and covered most external buildings until the onset of cladding in the early twentieth century.

 

Types of Walling

·         Ashlar faced cavity wall

·         Split faced cavity wall

·         Ashlar faced solid wall

·         Split faced cavity wall

There can also be stone features incorporated into other facades, such as stone quoins, window surrounds or string or coping courses.

The Natural Stone Masonry in modern Scottish Construction, gives some useful background information on differing types for walling and construction and typical design details and sketches.  It is important to read this document together with any new guidance in the relevant British Standards. 

Ashlar Walling

Ashlar walling should be designed to carry its own load, but not normally any load from the building so the stones tend to be smaller and thicker than cladding.  Course heights are typically at 300mm and thickness 100mm.  The stones can be set sizes or random. 

Split Faced Walling

The split faced walling is typically 100mm thick and manufactured from off-cuts from the masonry operation so the sizes are random, have a very low carbon footprint and are competitively price but can be limited on the variation of sizes offered. 

The split faced stone can prepared in three different ways.

1.      Machine split

2.      Machine split and dressed (the edges manually removed to give a move random finish to the wall)

3.      Machine split and dressed (the stone are hand pitched back 10mm to give a convex face to the stones)

Cavity Wall

Designed like a typical cavity wall construction but with a stone rather than brick as the outer facing.  Appropriate insulation, cavity ventilation, movement joints and fixings will need to be incorporated into the design.   

Solid Wall

The stones are normally directly attached using appropriate fixings to the loadbearing structure or may form part of the loadbearing structure.  The wall should be constructed to ensure no staining can migrate from the structure into the stonework.  Care needs to be taken relating to control of moisture so we would recommend looking at tradition designs where the surface water is diverted from the façade with regular projections.  The incorporation of a suitable DPC should be carefully considered but waterproofing the face or the rear of the wall to stop moisture penetrating is normally not advised.    

Joints and pointing

The joint sizes will depend on the manufacturing tolerances for the stones and the design, ashlar may be between 5 to 10mm, whereas the split walling will typically be between 10 and 20mm.  The pointing mortar can be, 1: 2: 8 or 9, white cement, lime, and Portland Stone Dust.  Lime mortars may be appropriate in some applications. 

Quality

All Albion Stone’s production is certificated to the ISO 9001 kitemark, meaning the quality system is independently audited by the BSI representatives.  The ashlar and split faced walling are normally manufactured from offcuts, not a specific bed, so the Technical Data should be based on an average figure for all beds of Albion Stone’s Portland Stone. 

Storage and handling

The pallets containing 1 tonne of walling stone are wrapped in recyclable plastic to protect the stone during the transportation, unloading and limited site storage, not for prolonged external storage.

Maintenance

The stone will not require cleaning to safeguard its durability; cleaning is purely a cosmetic requirment.

The effects of algae growth and bird fouling can be limited with a regular cleaning regime using water with a soft bristled brush. For the removal of this, and more ingrained contamination call the Lithofin Technical Line for specific guidance on cleaning this type of surface.

Cleaning and surface repair of a larger façade should be carried out in accordance with BS 8221‑1 and BS 8221‑2 and the Stone Federation guide to Best Practice on the Cleaning of Internal and External Masonry Surfaces guidance by suitably qualified operatives on a cycle depending on the building design, the local climate and orientation of the facades, and the levels of atmospheric deposits deemed acceptable by the client.