DRY STONE WALLING; REPOINTING; WET STONE WALLING; SYMPATHETIC RESTORATION

Information on my training and the standards to which I work: The DSWA (Dry Stone Walling Association of Great Britain (Est. 1968); patron HRH the Prince of Wales) has set the UK benchmark for training in building and repairing dry stone walls. It operates the only national series of progressive practical tests leading to the certificate of Master Craftsman in Dry Stone Walling. The scheme is designed to ensure that wallers achieve the highest standards of craftsmanship and the tests provide a nationally recognised accredition upon which customers can rely. I have completed the DSWA's training programme to Intermediate level and am able to repair and construct quality dry stone walls to industry standards.

Advice on rebuilding old walls: The main reason dry stone walls fall down is poor build quality. There are three prevailing types of bad craftsmanship: Poor or no foundations, trace walling and poor hearting. With trace walling the wall is built with the stone laid widthways and not lengthways into the wall. Poor hearting involves filling the middle of the wall with rubble, soil, mortar etc when it should have been built as a 'wall inside a wall' using flat stones. In many cases all three reasons cause a wall to collapse but sometimes just one is sufficient. When a wall is rebuilt, much of the original stone will be unusable due to its poor original quality and the fact that it has weathered; therefore it will be necessary to budget for some new stone. When undertaking repairs only a small quantity of stone may be required. However, a delivery from a quarry will may not suffice as it is unlikely the crucial foundation stones, through stones, and copes will be included in the consignment. Therefore it is necessary to go to the quarry and hand pick the required amounts of stones.

Below. Before: This wall was built without foundations, through stones, or a cover band and as it was dismantled I found trace walling and poor hearting.

Below. After: Most of the old stone was too small to build with and was either disposed of or used as hearting. To replace it I hand picked two tons of choice stones and the wall now benefits from substantial foundations.

Below: This wall in Burford was repaired using approximately 80% of the original stone. The other 20% was also built from used stone which I was fortunate enough to retrieve from a disused wall. I also cut back unwieldy shrubs and erected a closeboard fence as my clients required extra privacy.

Advice on building new walls. Dry stone walling can be one of the most expensive of all the boundaries available, mainly because it is labour intensive and may involve considerable materials and haulage costs. Other significant factors include ease of access to the site and the implications of where a wall is to be positioned: If for example it is to be built next to a pedestrian walkway where the working space will be limited, the area will need to be cordoned off, sign posted and lit at night in accordance with Highways Agency regulations. The quality of finish also affects price as ornamental pieces take longer to build than field walls. Some customers choose to provide their own stone and if this of poor quality the wall will also take longer to build. Experience dictates it is rarely possible to give a price per metre over the telephone as it always necessary to assess the site.

As speed affects quality when building a dry stone wall, the cheapest quote is not always a good deal. The difference between a well built and a poorly built dry stone wall can be seen straight away and is perhaps the best reason to retain the services of a fully trained waller. What may not be immediately apparent is that dry stone walls need to settle on an insubstantial base and it is therefore inadvisable to employ anyone who will build the dry stone wall on concrete footings. It is the friction of the stones rubbing up against one another as they settle which gives the wall much of its strength as it finds its own level over the years.


Stone or cement mortar coping? Cement mortar is brittle and unable to cope with the inevitable changes in level which occur whilst the wall settles. Many people choose it in the belief that it will make the wall more stable but in fact the opposite is true and eventually damage occurs. Stone coping (topper stones/cover bands) cost more but last longer, look better and give extra strength to the wall.

Picture below: Small stones are easily dislodged whereas large ones stay where they are put. The wall below may look fine but on further inspection it is possible to see that many of the larger stones have been 'front pinned' i.e. they have been underpinned with small stones which will, when weathered, eventually fall out adding to the instability of this wall.

Pricing:

Before I am able to give a rate per metre to build or rebuild dry stone walls it is necessary to first view the site to discover the implications involved in completing the work. The final price of a wall depends on the type of finish you require - if it is a field wall it will cost a great deal less than a high spec. ornamental wall. Figures usually start from £40 - £50 per face metre but this does not include the cost of the stone or digging the footings, building cheek ends, fixing the foundation stones into position, sorting/grading the stone, or any work on the coping. In addition is the cost of removing the waste stone and any arisings; site clearance after work is completed is also regarded as an extra and will be factored into the quote unless you wish to organise it yourself.

Unlike many contractors I never use cement mortar when building a new cheek end.

What I ask of my customer: That before I am invited to quote for a repair you make sure that the wall in question actually belongs to you. If the wall belongs to someone else, please discuss the possibility of a repair with the owner first and ask them to contact me.

These coping stones will press down on the wall and flex with it as it moves.

Below: Before

This is a field wall which had deteriorated during floods; most of the stone was unusable.

Below: After. New stone ensures a stock-proof wall

Below: Before

Below: After

REPOINTING and PROPERTY MAINTENANCE 

Repointing is charged from £50 per square metre (inc) plus materials and sundries. This work does create mess and the cleaning up necessary on completion will be factored into the quote unless this is something you wish to organise yourself.

Victorian brick walls are prone to movement and a lime mortar is essential.

Above: This photograph shows a North Oxford garden wall which had fallen into a state of disrepair. The old mortar was raked out and it is ready for repointing.

Above: This photo shows the same wall after it has been repointed with lime mortar. It will now last for many more years as further movement will be less of an issue.

N.B. Although it is common practice for many contractors to add cement to their lime mortar mixes there is no evidence - to my knowledge - which suggests this is of any benefit. There is however some evidence that it may contribute to failure of the bond.

What I ask of my customer: That before I am invited to quote to re-point a wall, you ensure that the wall in question actually belongs to you. If the wall belongs to someone else, please discuss the possibility of a repair with them first and ask the owner to contact me.

Project in Witney

Below: The photographs below show the front of the cottage after repointing.

Below: The photographs below show the back of the cottage after the repointing had been completed.

Below: This conversted barn in Buckland had suffered as a result of poor tradesmen's workmanship and I was commissioned to renovate many aspects of it.

Below: The quoins in these photos were severely weathered and I rebuilt them them using a specialist technique involving fillers and pigments which resulted in an econimical repair.

Below: The stone in this apex was severely weathered and crumbling badly (especially the metre at the hightest point). I replaced much of the stone whilst dressing and repointing the remainder.

Below: These photos show quoins which were completely replaced.

Cement mortar compared to lime mortar:

Why bother using lime when comparatively cheaper cement is available? Traditional building construction is based on the use of relatively soft and porous materials such as stone, brick, timber and earth used together with a lime based mortar for bedding and plastering. Buildings made from these materials usually have solid walls with no cavity and are often built on insubstantial foundations. They are therefore liable to settlement and movement associated with seasonal changes in ground conditions. Lime mortar is softer and weaker than the stone or brick which it bonds and is therefore able to accommodate slight movements caused by settlement or temperature changes without significant cracking. It is also permeable and allows evaporation of rising and penetrating damp from within the wall. It is this permeability, or 'breathing', which helps to keep the building dry inside without a damp proof course or chemical treatments.


What is wrong with cement mortar? Modern cement pointing is very different from lime mortar. It is hard and brittle, much less porous and sometimes completely water-proof. Its use on traditional masonry is damaging in several ways...

Cement pointing is harder than soft brick or stone and is too rigid to accommodate settlement or movement in a wall or house. When movement occurs the edges of the stone or brick are forced against the hard mortar spaling the masonry and cracking the mortar itself.

Below: Here even the wrong type of sand has gone into the cement mortar mix and the stone has deteriorated badly. It is in desperate need of repair.

Below: Further damage is caused by rainwater seeping into the cracks in the pointing and around the edges of the stones. As the mortar is not permeable this moisture cannot evaporate from the mortar joint once rain stops. Instead it is forced to evaporate through the face of the brick or stone and soluble salts present (sodium sulphate for example) in the water crystallise in the surface layers of the masonry leading to crumbling and decay. This is sometimes so severe that the entire face of the stone is lost and the hard cement pointing is left standing proud. Further rainwater is trapped and the decay continues. The concentration of trapped water in the masonry also increases its susceptibility to frost damage in winter.

In contrast soft lime mortar allows moisture movement and, being more porous than the masonry, encourages evaporation and salt deposition in the mortar joints. Thus it is the mortar which decays and not the stone or brick. It is much easier and cheaper to repoint a wall than to repair or replace damaged stone and there is less loss of important historic fabric.

Above: This style of re-pointing may look attractive at first glance, but it has been done with cement mortar and trowelled in. Although many bricklayers and builders may create this effect, it indicates insufficient training and experience in traditional methods and materials. A 17th Century craftsman would not have recognised this at all: Lime mortar should have been used and the final effect should be smoothly brushed joints with the aggregates in the sand showing.


Below: Before: For some reason the previous contractor had smeared a rich cement mortar very thinly over the joints and stone; in effect waterproofing the whole house and turning it a horrible grey colour.

Below: After: I raked out the joints with masonry friendly tools; applied the correct lime mortar mix and used the right brushes to achieve this professional affect. Not only does it look better, it has increased the saleability of the house.

Sympathetic restoration: On older houses some of the original masonry will deteriorate so badly it needs to be replaced. Here what is needed is experience as only small sections can be restored at a time - only so many pieces of stone can be removed without compromising the structural integrity of a house or wall.


The restoration of a property does not just mean hydraulic lime rendering, re-pointing or stone replacement but can extend to organic paints, sheep's wool insulation, lime wash and imperial hand made bricks.


Cement render: This causes slightly different problems. Hairline shrinkage cracks inevitably form in the surface of the render as it sets or afterwards by slight movement in the wall. The rainwater is drawn by capillary action into these cracks and then diffuses into the wall. Once inside the wall this moisture, together with any rising damp, is trapped as it cannot evaporate through the hard, impermeable render. Moisture levels start to build up in the wall and the moisture tends to diffuse towards the inner surface of the wall resulting in internal dampness and damage to plaster and decorations. So, strange as it may seem, applying a waterproof render can actually increase levels of damp inside the house or wall. A porous lime render encourages evaporation of moisture from its surface, helping to minimise the effects of penetrating and rising damp.

Patios: I also re-lay and re-point patios.

Below: A rotary washing line pole had been sited in the middle of this patio; rain water had got in through the hole and was unable to escape due to the fact that a solid cement mortar base had been layed. All the slabs had to be re-fixed before I could do any re-pointing.