Best Practice Guide

Introduction

Our best practice guide uses SouthGate shopping centre in Bath as an exemplar project.  The specification has been included for example purposes only.

Forest Pennant was selected by Bath City Council as the principle hard landscaping material for SouthGate, some 10,000m2 .  Upon completion of the works Bath City Council commissioned a pattern book for future development in the city, from which our best practice guide has evolved.

Note: Code references are in line with the NBS Codes where applicable.

Materials

Specification 310A: Natural Stone Paving Slabs – Forest Pennant

Standard BS EN 1341
Supplier Forest of Dean Stone Firms Ltd
Quarry Barnhill Quarry, Gloucestershire
Stone Type Forest of Dean Pennant Sandstone
Product Forest Pennant paving (mixed colour)
Finish Diamond sawn (free from saw marks)
Sizes Gauge Width Fixed gauge width.

600mm (43%), 450mm (37%) and 300mm (20 %). Note: Percentages are by area.

Length Random length.

Ratio not to exceed 2:1 up to max. 900mm

Thickness 50mm upwards (location dependent)
Plan dimension deviation class P2
Diagonal deviation class D2
Thickness deviation class T2
Joint widths 8mm +/- 1mm, set using plastic 8mm spacers
Arrises Square
Freeze/Thaw Resistance Class F1
Flexural Strength (MPA) 15.0
Abrasion Resistance (mm) 18.5
Slip/Skid Resistance (USRV) 83
Water Absorption (% by mass) 2.5
Petro-Graphical Description Fine to medium grained sandstone

310B: Natural Stone Setts – Forest Pennant

Standard BS EN 1341
Supplier Forest of Dean Stone Firms Ltd
Quarry Barnhill Quarry, Gloucestershire
Stone Type Forest of Dean Pennant Sandstone
Product Forest Pennant paving (mixed colour)
Finish Diamond sawn (free from saw marks)
Sizes Gauge Width Two fixed gauge widths laid alternately.

200mm and 400mm long and 120mm wide x various lengths 240mm (43%), 220mm (37%) and 200mm (20 %).

Note: Percentages are by area.

Length Random length as detailed above
Thickness 50mm upwards (location dependent)
Plan dimension deviation class P2
Diagonal deviation class D2
Thickness deviation class T2
Joint widths 8mm +/- 1mm, set using plastic 8mm spacers
Arrises Square
Freeze/Thaw Resistance Class F1
Flexural Strength (MPA) 15.0
Abrasion Resistance (mm) 18.5
Slip/Skid Resistance (USRV) 83
Water Absorption (% by mass) 2.5
Petro-Graphical Description Fine to medium grained sandstone

615A: Control Samples

Control panels of a suitable size will be constructed off or on-site, as a true representation of the colour and appearance of the finished materials. They will also establish the standard that is required from the installer. To achieve the best finish it is imperative that the right skillset is employed by the contractor/sub-contractor.

620A: Adverse Weather Conditions

Temperature:

  • Do not lay or grout paving if the temperature is below 3o C on a falling thermometer or below 1o C on a rising thermometer
  • Do not use frozen materials
  • Do not lay on frozen or frost covered bases

Paving with mortar joints and/or bedding:

  • Protect from frost damage, rapid drying out and saturation until mortar has hardened
  • Do not apply jointing materials when the ambient temperature exceeds 25o C and rising

625A: Laying Paving – General

Criteria for selection and rejection of stone:

  • Contractor to check compliance with the specification and approved sample panel prior to laying on site. In addition to the specified performance requirements any stone found to have defects such as hairline fractures, surface contamination, abrasions, chips, coal deposits or other inclusions which may cause a weakness through or in the surface of the stone should be rejected and replaced by the supplier free of charge
  • Paving shall be selected and laid using three pallets on-site, to avoid “striping” and uniform colouration

Final appearance:

  • Smooth and even with regular joints and accurate to line, level and profile

Falls:

  • To prevent ponding site operatives should consider the levels and gradients to be achieved over the finished paved surface prior and during the coursing and installation process

Installation

Bedding, Bonding & Jointing:

  • In virtually all locations, and as is the case at Southgate, Forest of Dean Stone Firms Ltd advocates the use of BS 7533 compliant mortar systems.

Sample Method Statement and Pictorial Installation Guide

Laying of Natural Stone using a BS 7533 compliant mortar system which consists of a bedding mortar, priming and bonding mortar and slurry jointing mortar laid upon a concrete road base or supporting structure.

Install_image threeLaying Paving Units

  • Ensure that all three part mortars are mixed in accordance with the manufacturer’s instructions. 
  • Do not mix more than will be used within approximately one hour at an ambient 20OC. 
  • Ensure that the concrete substrate is sound, free of loose material and has been thoroughly cleaned with water.

Apply a coat of priming mortar to the road base/supporting structure immediately prior to applying the bedding mortar, which is normally 50 mm thick, and ensure that primer and bedding mortar is restricted to the localised area of paving to be fixed.  Note that priming coats will stick to virtually anything and be easily walked onto the surface of finished materials.

  • Paving units should be thoroughly cleaned and washed with water prior to use.
  • The underside of each unit should be coated with a layer of priming mortar by brush immediately prior to the paving being laid, taking extra care to avoid spillage of priming mortar on the surface of the paving.
  • Paving units should be laid immediately, set out and positioned firmly into place and levels.
  • Post laying, the surface must be thoroughly washed with clean water to remove any surplus mortar on the surface of the paving units.
  • The paved area should be quarantined to prevent access, including pedestrians, for a period of at least one day in order to avoid disturbance and displacement of paving units on the fresh bedding mortar. However joint grouting may be undertaken on the same day as laying if it is possible to be carried out by operatives without standing upon the freshly laid surface.

Install 3_image fiveGrouting the Paving

  • Immediately prior to grouting, it must be ensured that all joints are free of debris and the paving surface thoroughly wetted and kept wet until the grouting process has been completed.
  • Mix the grouting mortar in accordance with manufactures instructions and apply without delay.
  • Do not store liquid mortar other than in transit from the mixer.

squeegee_image sixImmediately after mixing, the grouting mortar is spread onto the surface and carefully worked into the joints using a suitable soft rubber squeegee. A quantity of mortar should be maintained upon, and constantly moved over, the surface in order to repeatedly top-up the joints in which the mortar may have settled following initial placement.

When the joints are full and will not accept any more mortar, a suitable squeegee should be used to remove as much excess mortar as possible, keeping the surface constantly moist, using a soft spray or mist of water.

The surface may be rinsed clear of the thin film of mortar remaining, and when the mortar has hardened sufficiently, the surface can be thoroughly cleaned with either brush and copious amounts of water, or a proprietary cleaning machine employing power-driven sponge belts.

TIP: It is imperative that the cleaning must be carried out very thoroughly and no mortar must be allowed to remain on the surface of the paving.

Quarantine periods and opening to traffic:

It is recommended that batch samples are taken and allowed to site cure for testing in respect of strength gain prior to opening areas to vehicular traffic making reference to the requirement for the minimum compressive strengths for each project.

MAINTENANCE & PROTECTION SYSTEMS

Forest of Dean Stone Firms recommends a post-completion deep-clean by a specialist cleaning contractor prior to handover. 

Please contact the company for details on suitable treatments and proven cleaning and maintenance contractors.

Forest Pennant is a brand name of Forest of Dean Stone Firms Ltd.  All Forest Pennant products are manufactured and supplied by the company using its unique source Carboniferous Pennant sandstone extracted from Barnhill Quarry in the heart of Forest of Dean.

For a free estimate or to find out more about our products and services please get in touch

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