Traditional Handset Cladding

Traditional hand fixed cladding is still widely used for Portland Stone cladding, particularly for the medium and smaller projects. The traditional hand fixed cladding system typically carries the load of the cladding to a load bearing fixing situated at the floor plate. The stones above are simply restrained using Restraint fixings.

Traditional Cladding

General

The design team should establish the maximum movement and shortening of the frame and how that will be accommodated in the stone cladding.

We recommend the early appointment of the specialist stone cladding designer to develop the design teams, proposals. Utilizing our technical data they will be able to provide the stone thickness calculations, location and design of the fixing and most aspects of the stone fixing system.

Fixings

The fixings should be able to withstand the imposed loads on the cladding including dead loads, wind pressure and suction.

The fixings are normally either Loadbearing, to carry the dead weight of the cladding, or Restraint to withstand the lateral loading, normally wind pressure.

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Fig. Restraint Fixings

 

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Fig. Load bearing Fixings

Cavities

The cavity between the stone cladding and the backing structure will allow space for the fixings and bolt heads, stone and structural tolerances, insulation, an air gap to minimise transmission of rainwater and allow for free draining of any trapped moisture.

The air gap should be at least 10mm wide after all the construction tolerances have been taken into consideration. Weep holes will need to be designed where trapped moisture accumulates at cavity trays and at the d.p.c. level


Cavity Fire Stops

The cavity design needs to incorporate cavity barriers to prevent the spread of fire both vertically and horizontally and reduce the effect of fire on the fixings.


Insulation

The insulation needs to be non-combustible, rot and vermin proof and non-absorbent, and need to be at least 10mm from the back of the stone cladding.


Cavity Trays and DPC

The cavity trays and the d.p.c. should be formed from materials that will not degrade and stain the stonework and incorporated in a sufficiently wide bed joint in accordance with the manufacturer guidelines

Jointing and Pointings

Joints should be weathertight whether they are loadbearing or designed to accommodate movements of the cladding. Where the joints are narrower than 5 mm, the manufacturing tolerances and the effectiveness of the jointing material will need to be carefully reviewed.


Compression Joints

Compression joints are horizontal movement joints and are designed to accept the vertical movement of the structure
They are normally situated at each floor level immediately under the course supported by the load bearing fixing and the width should be proved by calculation and is unlikely to be less than 15mm.


Movement Joints

Movement (Expansion) joints are vertical. The spacing and the widths of these joints need to be designed to accommodate the anticipated movement, but the distance between the joints should not exceed 6m and should be between 1.5m and 3m from any corner. The joint width should be proven by calculation but is unlikely to be less than 10mm.

The spacing and the widths of these joints need to be designed to accommodate the anticipated movement, but it is recommended that the joints are not less than 10mm per 6m length of cladding and should be between 1.5m and 3m from any corner.

Sealants

Movement joints need to be filled with a sealant that has a good service life (above 20 years), has good adhesion properties, will match the colour of the Portland Stone and will not cause staining of the stone. A primer may be necessary.

Mortars

The mortars for jointing and pointing should match  the colour of the Portland Stone and be slightly weaker than the stone itself. 

To ensure the colour match, Portland Stone dust should always be used as the  aggregate. The recommended mixes are set out below:

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Fixing Contractor

We recommend that the stone and the fixing contractor are selected as early as possible in the project programme.

The stone fixing sub-contractors will normally take responsibility for the entire stone package including stone drawings, stone procurement and stone fixing on site. Therefore it is vital that the selected company has the necessary experience and expertise

Specification Clause