Stone on Precast cladding is stone panels on precast concrete cladding units. The technique was imported from the USA in the 1950s and has a proven track record. The cladding façade will look very similar to the traditional handset cladding and often Stone on Precast projects will include elements of handset stone.
The individual stones are supported by the series of dowels and they do not rely on adhesion with the concrete.
The debonding membrane between the concrete backing panel and the individual stones will allow for differential movement between these different products.
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.
The manufacturing tolerances as set out in BS 8298 allow for typically 5mm (+- 1.5mm) joints for all but the largest stones. Please note that the maximum width of a mortar joint is 13mm, but a sealant filled movement joint can be up to 30mm wide.
Cement Lime Mortars
The mortars for jointing and pointing should match the colour of the Portland Stone and be slightly weaker than the stone itself.
We recommend that the stone and the Stone on Precast contractor is selected as early as possible in the project programme.
The designer should be aware of the recommended lead-in period for the supply of stonework and the availability of production slots in the pre-cast company's factory.