Flag Paving

“The following guidelines are applicable for both concrete flag paving and natural stone flags. If further assistance is required, please contact the Technical Helpline 01335 372222”

Design standards

All installations should be detailed and constructed in accordance with the relevant British Standard. This is BS 7533: Part 4 for installation. For structural design, please refer to either BS 7533 Part 12 or the Interpave Design Guide.

Laying

Select site category:

Heavy duty applications of more than 60 commercial vehicles per day (over 1.5T unladen)
Medium duty applications of 60 or less commercial vehicles.
Medium-light duty applications – 5 or less commercial vehicles per day.
Light duty applications – no commercial vehicles.

Select laying method

  • Flags laid rigidly for all categories
  • Flags laid rigidly for category 4 only
  • Flags laid flexibly for categories 2,3,4.

Laying method

Flags laid rigidly for all categories

For this category, a hydraulically bound road base should be used and should be designed in accordance with the relevant standard (see above).

The back of the flag and the top surface of the roadbase should be primed with a slurry of the material that will be used in the joints. This is to ensure a good bond.

The laying course material should be a modified mortar as specified in BS 7533: Part 4 and spread to give a depth of 30 mm after compaction. Cement sand mortars are not suitable for use in this method.

The flags should be laid with a 6-10 mm joint.

A minimum of 12 hours after laying, the flags should be thoroughly wetted and the jointing material, as specified in BS 7533: Part 4 in slurry form, is spread over the entire surface. The material should be moved towards the open joints.

Once the joints are full, the flags should be wetted again and a squeegee used to remove excess mortar.

The area should not open be open to traffic until the bed and joints have reached sufficient strength.
Guidance should be sought from the mortar suppliers.
The flags should be compacted down using a paviors maul.

Flags laid rigidly for category 4 only

The laying course should consist of a workable mix of 1:3 cement sand mortar, thickness between 15 and 25mm after compaction.

The flags should be laid with a 6-10mm joint.

These should be filled within 2-3mm of the surface of the flag with a 1:4 cement sand mortar and pointed work as proceeds.

The flags should be compacted down using a paviors maul.

Flags laid flexibly for categories 2,3,4

The laying course should be fine aggregate to BS EN 12620 Gf 85 0/04 (mp).
The thickness of the laying course after compaction should be 25 mm.

This can be done by either:

  • Screeding the material to give the required depth after compaction. (A small trial area may be required to determine the amount of surcharge). The top 10 mm should then be loosened with a rake.
  • 25 mm of laying course material should be screeded out and compacted. Then a further 10 mm of loose material screeded out on top.

The flags should be laid with a 2-5 mm joint that is filled with kiln dried silica sand to BS EN 12620 Gf85 0/04 (mp).

Note: the gradings for the laying course material and joint filling material may be found in BS 7533: Part 4.

The flags should be compacted using a vibrating plate compactor in accordance with BS 7533: Part 4.
Top up the joints with kiln dried silica sand as necessary and during early life.
After laying light coloured paving on site, care should be taken to protect from dirt and detritus while the remaining construction works are completed.

Successful installations

The key factors in designing successful paving installations are (in summary):

Anticipation of applied loads
In particular, the ability of flag paving to support loads is dependent on specification of the correct thickness for sub-base and bedding and for the flags themselves.

Pre-planned drainage
Drainage method should be considered before installation, with adequate falls to dished or linear drainage systems for quick removal of surface water.

Appropriate sub-grade
Well-compacted to appropriate thickness, with all sub-grade drainage completed and, where necessary, measures taken to stabilise soft ground.

Well-prepared sub-base
Systematically layered and properly compacted to a close-textured surface using materials appropriate for the paving type concerned.

Correct bedding and laying
Bedding materials must be protected from adverse weather prior to laying. Paving should be laid with correctly spaced jointing. Bedding layer damage and creep can be minimised by working up slopes and/or away from edge restraints.

Stable edge restraints
Required to provide sufficient lateral support for the paving during laying and long-term.

Careful detailing At edges, around access points (e.g. manhole covers, drain inlets), adjacent to kerb crossings and around obstructions.

Installation planning

Edge restraints

Suitable kerbing or edge restraints are required. Most proprietary kerbing, channelling or edging systems are suitable, including the following Charcon systems:

  • Countryside Classic Kerb.
  • Block Kerb.

These should be bedded in concrete and haunched in accordance with BS 7533: Part 6.

Sub-grade If ground is soft/poor quality, consider laying a geotextile membrane (eg. Terram) or capping layer to help support sub-base.

Sub-base

Material: (for most cases) granular sub-base type 1 (in accordance with clause 803*).

Alternatives: cement-bound material 1-3 (in accordance with appropriate clauses*).

  • Compacted depth: 100 mm min.
  • A binding layer of fine material may be required for an open-textured sub-base.

* Clauses refer to Specification for Highway Works.

Preparation (all flags)

Sub-grade

Clear top-soil: complete sub-grade drainage.
Excavate and back-fill soft spots: compact well throughout.
Protect sub-grade from adverse weather.
Lay geotextile fabric or capping layer (if specified/required).

Sub-base

Prepare in accordance with the Specification for Highway Works.
Lay and compact in layers to a close-textured finish.
Open-textured sub-bases may require a binding layer of finer material.

General principles

Lay paving immediately on prepared bedding, do not leave bedding exposed to weather and/or overnight.
To avoid bedding layer damage and creep, lay paving units up slopes and/or away from edge restraints.
Stand on previously laid paving when placing next row.