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Paving Units – part 3



Paving units of concrete, clay, brick, timber, stone or tile are popular and attractive options, though it’s essential they are installed correctly and designed to manage run-off and permeability requirements.


The following is the third in a three-part guide on how pavers should be best selected, installed and managed.

Ceramic (fired clay) tiles


Ceramic (fired clay) tiles are manufactured from a proportioned mix of clay, fillers and flux. Most flooring tiles are formed by either dust pressing (a dry mix is compacted into a mould under high pressure) or extrusion (stiff wet clay is squeezed through a die and then wire cut to size and thickness). After forming, tiles are typically dried, glazed to colour and to make the surface impervious (this does not apply to terracotta or porcelain) and kiln fired. The firing process determines the vitreous quality (water absorption or porosity) of the finished tile.

Tiles come in a wide range of types, sizes, finishes and quality – not all tiles are suitable for all applications (see Table on next page).

Tiles suitable for exterior walking surfaces are:

  • Terracotta – extruded, hard unglazed tiles of low permeability and high abrasion resistance, used for pool surrounds and entrances.

  • Porcelain – dust-pressed, fully vitrified, dense, low water absorption (below 5%), abrasion-resistant tiles, available in natural smooth or ground and polished finishes.

  • Monocottura – single-fired tiles that can range from soft wall tiles to hard high-strength tiles suitable for heavy foot traffic.

  • Monopressatura – dense abrasion-resistant glazed tiles.

  • Quarry – extruded clay or earthenware tiles usually unglazed and manufactured to less strict tolerances than pressed tiles (lower-quality porous tiles are not suitable for areas subject to freezing and thawing).

  • Mosaic – usually small, glazed tiles supplied on 300 x 300mm ready-to-lay sheets.

The separate components of a tiled finish are the:

  • Supporting structure (timber, concrete).

  • Substrate (material the tiles are applied to – plywood, fibre-cement, concrete).

  • Adhesive.

  • Tiles.

  • Grout.

  • Sealer for absorbent tiles.

  • Waterproofing (for tiles within wet areas of a building).

For outdoor use, plywood and fibre-cement substrates must have a waterproofing layer (roofing membrane, acrylic or a resin-based system) between the tiles and the substrate to prevent wetting of the substrate and the framing.


Natural stone tiles


There is a range of natural stone tiles or cobblestones suitable for use as exterior walk-on paving. As with tiles, they are adhered to a rigid substrate.

Basalt


A very durable and abrasion-resistant dark-coloured fine-grained igneous rock of volcanic origin with a high percentage of iron and magnesium.

The textures vary. A polished finish is attractive, but a honed finish will provide better slip resistance when used for walk-on surfaces.

Other finishes include diamond sawn, bush hammered, sand blasted and natural face. Basalt is also commonly referred to as bluestone.

Granite


A granular, igneous rock consisting mostly of quartz and feldspars, which is very durable, abrasion resistant and will maintain its appearance indefinitely.


Limestone


A sedimentary rock composed of calcium carbonate that is generally softer than marble. It is normally white but can be brown, yellow or red due to iron oxides and blue, black or grey if carbon impurities are present. Limestone stains easily and is difficult to clean unless a sealer coat is applied. Commonly used as paving or stonework.


Marble


Strictly, limestone that has recrystallised under pressure and temperature, but may refer to any limestone that can be polished. Marble is dense but is easily scratched and so should not be used in areas of high abrasion. Colour can be affected by staining. Commonly used as a paving material.

Sandstone


A sedimentary rock composed of sand-sized grains of quartz bonded by a matrix of other materials. Colours usually range from white to brown and green. Moderately durable but stains easily and is difficult to clean unless a sealer coat is applied.


Slate


Natural slate is a compact and fine-grained metamorphic rock formed from clay, shale or volcanic ash, but a wide range of geologically different materials such as siltstone, mudstone, shale, marl or limestone may be classed as slate. A wide range of colours is available. Slate is quarried, cut into suitably sized blocks then split to form the units. Slates can be used as a roofing material or as a floor finish. As a walk-on surface, it is hardwearing and durable in a range of finishes, but high-quality types are significantly more expensive than some of the types used for domestic applications.

Greywacke


Tough sedimentary rocks mostly composed of grey to dark grey, poorly sorted layers of sandstones and siltstones consisting of angular to subangular grains of quartz and feldspar together with an assortment of small rock fragments set in a compact, fine matrix. Greywacke is mainly crushed for roading and concrete aggregate and as boulders but is also available as cut blocks (dimensioned stone).


Schist

A metamorphic rock with a plated structure where the component flaky minerals are visible to the naked eye. The striated structure of the rock encourages disintegration, and these rocks are more prone to weathering and erosion than greywackes. Schist is available in a range of colours, depending on the location of the quarry. Paving sizes of up to 2m are available depending on the stone type.

Quartzite


Consists of firmly cemented quartz grains from the metamorphosis of sandstone. It is distinguished from sandstone by fracturing across, rather than along, the line of cementing material.


Using ceramic and stone tiles

Key criteria for successful direct application of tiles and stone tile floor finishes:

  • Ensure the tile module fits the area being tiled (or design to suit the tile module) to minimise the need to cut tiles.

  • A maximum deflection for all substrates of not more than 1/360th of the span under both live and dead loads, except that a deflection of 1/480th of the span should be used when the substrate spans over 3.0 m and/or large (>400 x 400mm) tiles are used.

    • A maximum variation in plane of:

    • 5mm in 3m thin-bed adhesive over concrete.

    • 10mm in 3m thick-bed adhesive over concrete.

    • 20mm in 3m thick-bed mortar/screed over concrete.

    • 5mm in 3m framed construction with sheet substrates.

  • Adhesives must be used in accordance with the manufacturer’s instructions. The most commonly used adhesives are sand cements, polymer-modified sand cements, single-part polymer-based organics and two-part polymer-based organic adhesives that may contain cement.

  • Movement-control (flexible) joints must be installed:

    • At changes in plane.

    • At no greater than 4.5 m intervals.

    • Where there is a movement-control joint in the substrate.

    • Where the substrate material changes (where flexing of the structure will occur).

    • Where the type of tile used changes.

  • Grout filling of joints must be carried out so that the grout (usually cement based) is well packed into the joints. (Note that grouted joints are not waterproof.)

For comprehensive information on tiling, refer to the BRANZ Good Practice Guide Tiling.




This article was first published in BRANZ’s Landscape Construction book, Second Edition and is reproduced with permission.

The book covers the design, building and planning rules as they apply to landscape construction and provides guidance on design and construction to ensure good practices are followed. It can be purchased at www.branz.co.nz.

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