Paving

Portland Stone paving has the advantages of excellent slip resistance and  good durability, which is unusual for most Limestones and has therefore encouraged its use as a paving material. The shellier Whitbeds, such as Grove Whitbed, give a good texture and very natural appearance to the stone.

Paving Substrate

There are a number of factors that need to be considered by the designer, including the paver size and thickness, but most importantly the substrate that will provide the strength.


Base

It is important that the base provides a solid foundation for the paving and where movement is a possibility it may be wise to use a reinforced strong concrete base.

The paving needs to be laid to a fall, typically 1:50 to ensure that water runs off and puddling does not occur, which can cause slipping hazards in freezing weather, as well as a concentration of damaging salts as the puddle evaporates. Saturated stones are more liable to frost damage in very cold weather, so good water management is a very important aspect of the stone paving.

Consideration should also be given in the design to potential run offs onto the paving. These run offs can wash nutrients and debris that can encourage the growth of algae or potentially damaging salts or de-icing salts from surrounding roadways.

The base should be laid to an accurate level, say +-15mm to ensure that the bedding is kept in an appropriate range, say 25-75mm thick. The base and bedding need to be free draining to avoid trapping moisture, salts and staining becoming concentrated in the stone.


Bedding

It is imperative that only clean river washed sand and white cement are used in the bedding and the grouting to avoid the possibility of staining being drawn into the stone.

Installation

The stone should be laid by an experienced stone mason, not a general builder. The stones should be carefully handled and accurately laid with joints at 6mm +-1.5mm.

The grouting is normally clean washed sand and white cement, but Portland Stone Dust in place of the sand is sometimes used.

Technical Properties

External paving provides one of the harshest environments for stone. Any stone used in this situation must perform well in a series of differing tests: Salt Crystallisation, Freeze Thaw test, Slip Resistance, Abrasive Resistance and the strength tests.


Paver Thickness

Annex B in BS EN 1341 provides the calculation of breaking loads for pavers. Our Paving Annex 1 provides the calculation for paving thickness. Please view it here

Albion Stone's Portland Whitbeds and Portland Roach perform very well in all these tests and are often used for external paving. The Basebeds perform less well in the Salt Crystallisation test and are therefore not recommended for external paving. For more detailed test results see our Technical Data Sheets. These can be found on each separate bed page.

Site Practice

All products leaving our works are packed in a manner to ensure safe delivery to site.

This entails protection by CFC free polystyrene strips, shrink-wrapping and delivery on suitably sized pallets, frames or crates. These normally contain a maximum of 1tonne for safe handling on site. It should be noted that it is the customer's responsibility to ensure safe unloading of delivery vehicles.

A suitable storage area will need to be set aside for the stone, which should be stored on firm, level surfaces and, to avoid contamination, should be sited away from wet or muddy areas. Storage should be as near as practical to the areas of working in order to minimise handling, damage and waste. Pallets should not be stacked on top of each other. Should it be necessary to store the material on site for any length of time, it should be protected from the elements and the environment.

The designer will need to be aware of the manual handling regulations and ensure appropriate lifting equipment is available to move and fix the heavy stones.

Maintenance

After initial laying, the paving may dry inconsistently and a small proportion of organic compounds that are water soluble may migrate to the surface of the stone.

This slight discolouration will settle down very quickly and will not require any additional cleaning. We do not recommend sealing the stone for external paving.

In protected areas, the stone may require light brushing with water and a mild detergent, followed by a clean water rinse in order to remove air borne dirt. Areas beneath trees and persistently damp sheltered areas may be subject to algae growth, particularly during the first two years of installation.  This growth can be controlled by brushing with a stiff broom or gentle jet washing, ensuring the grouting is not dislodged, and/or the application of a specialist algaecide.

As with cladding, any defective or leaking rainwater pipes that spill onto Limestone paving will over a period of time cause a decline in the condition of the affected units and should be rectified. Rust staining and other contamination caused by external ferrous items such as gate hinges should be ascertained and allowed for or properly maintained.

De-Icing Salts and Chemicals

All porous stone paving is susceptible to damage by the application of de-icing salts or most chemicals onto ice already established on its surface.

The rapid localised rise in temperature can effect spalling on the face of porous natural stones. The situation is then further aggravated by the ingress of this salt and water solution into the stone causing the face to become saturated. The salt ingress will then crystallise, causing further spalling on the surfaces.

Albion Stone does not therefore recommend the application of de-icing salts or compounds. There are non-corrosive products such as Clearway 6s (Solid) and IceBlastPlus (Liquid) that can be applied but at the time of writing, although they have been tested to the aviation specification no tests have been carried out on natural stone. It should be noted that if ice has not been removed by manual methods then care should be taken to avoid slipping on the material.

Specification Clause

Q25 - Natural Stone Slab/Brick/Sett/Cobble Paving