Q: I am building a driveway using granite setts. Should I bed them in sand or fix them with mortar?

For small works of this type I would recommend the considerably easier option of bedding in sand. Domestic driveways are unlikely to be subjected to heavy use or regular cleaning maintenance using street scrubbers and other machines that public areas get and can remove loose bedding and jointing materials.

If there are any problems, it is much easier to lift the setts and re-bed them if you have used sand. Eventually the joints will need topping up as the sand will invariable settle and some will be lost but it is a simple operation.

There is now also another very good reason why I would recommend bedding setts in sand and that is a recent addition to the Building Regulations. Controls have now come in to regulate changes to front gardens of domestic properties in an attempt to combat rain run-off that can result in localised flooding when people put a hard cover on their gardens, usually to give themselves parking spaces. Planning permission is now required when installing any hard surface that exceeds 5m2 .

So many people have put hard surfaces on their front gardens, resulting the rain running off into carriageways rather than soaking into the earth that the drains cannot cope. During increasingly common heavy rains that are blamed on global warming, drains may cause sewage and other pollutants to enter the river system, causing a range of environmental damage and health hazards. More details on planning are given on the Communities & Local Government Planning Portal at: www.communities.gov.uk/publications/ planningandbuilding/pavingfrontgardens

One way to avoid planning permission is to use porous materials, which would include setts bedded in loose sand. This allows rainwater to run into the ground rather than being shed to drains. The alternative is to ensure that any water run-off is to a lawn or other area where it is then able to drain naturally.

You must remember that it is useful to obtain confirmation that planning permission is not required, which usually costs a small sum but is worth it to avoid taking a gamble.

If you were to choose to fix the setts in mortar the main recommendation is that the base must be solid – which really means concrete. Any potentially flexible material, such as asphalt or aggregate, will move and cause the inflexible setts to crack and collapse.

Another common problem is not installing kerbs. Kerbs restrain the setts and stop them moving laterally. Lateral movement can, again, lead to cracking and failure. For this more complicated construction the guidance given in BS7533 should be followed where appropriate.

Fixing setts in mortar must be carried out with the utmost care to ensure the setts are strongly bonded to the mortar bed and each other with filled joints. This means using good quality proprietary materials and following a strict set of procedures such as washing the setts free of dust just prior to their use.

The use of ordinary sand and cement mortars is not recommended as these rarely have the necessary performance qualities required. Good mortar manufacturers and natural stone sett suppliers can usually provide further advice on these matters.

Reference: BS 7533. Pavements constructed with clay, natural stone or concrete pavers. Parts 7 and 10 cover setts while Part 6 covers kerbs. Published by the British Standards Institution, London, England.

Barry Hunt is a Chartered Geologist and Chartered Surveyor who has spent 20 years investigating issues relating to natural stone and other construction materials. He now runs IBIS, an independent geomaterials consultancy undertaking commissions worldwide to provide consultancy, inspection and testing advice. Tel: 020 8518 8646

The advice offered in answer to readers’ questions is intended to provide helpful insights but should not be regarded as complete or definitive. Professional advice should always be sought with all stone-related issues as each problem will inevitably have its own unique set of circumstances.