Pointing a building with lime is not necessarily expensive. What can be expensive, time consuming, and unpredictable, is the preparation of the wall surface.
This consists of the removal of the existing cement pointing, the cleaning of the joints between the stonework, and the rectification of any underlying issues such as degraded mortar or voids within the wall.
For lime pointing to function well, all cement pointing must be removed and the joints between the stones must be raked out to a depth of at least 25mm and be cleaned of all dust and debris. If areas of cement pointing are left in situ, they will inhibit the evaporation of moisture from the core of the wall.
If the joints between the stonework are not free of dust and debris prior to pointing, the lime may not adhere well to the stone, and will be more likely to allow moisture to track through.
When a clay cored wall has been cement pointed for many years, it is likely to be suffering from hidden issues such as degraded mortar and from the formation of voids within the wall.As has been discussed on our blog already, cement pointing is liable to exacerbate the erosion of surrounding stone. Once this process of erosion has begun, it is much easier for plants to take root in the wall. The roots of the plants break up the clay mortar and when they die, they introduce organic matter. These processes degrade and compromise the mortar. Degraded mortar must be removed and replaced with new lime or clay mortar before re-pointing.
When a clay cored wall with failed pointing has been subjected to driving rain or to a leak from faulty guttering, voids may develop within the wall. When water trickles through the pointing, the clay core of the wall is softened and may wash away. Over time this creates voids which affect the thermal efficiency and weather resistance of the wall. These voids provide a weak point where moisture can condense, concentrate, and trickle down through the stonework. For a rubble stone wall to function correctly, it is essential that these voids are thoroughly cleaned out and filled with a breathable mortar.
Pointing with lime is not necessarily expensive. Good thorough pointing with properly carried out preparation often is. An expensive estimate for lime pointing is no guarantee that the work will be done properly, but a cheap estimate almost certainly guarantees that it will not.
I have an old damp building - which areas should I prioritise?
In the world of traditional building restoration, we talk a lot about reinstating breathable finishes using lime and clay. Although this is an important tool in drying out old wet buildings, it is only one piece of the wider puzzle. It is wise to consider the building as a whole, and to prioritise problem areas in a strategic and considered manner.
Aside from breathable finishes, it must be ensured that the building has a good ‘hat and boots’. By ‘hat’ I mean the chimney, rainwater goods, and roof. By the boots I mean the drainage at the foot of the wall. These two areas are often by far the most cost effective to address. Leaky chimneys and gutters cause or contribute to the vast majority of the problems we commonly see in old buildings. Rainwater is concentrated in these areas, and if faults with them are present and are not addressed, extensive damage can be caused to the walls.
Incorrect drainage at the foot of a clay cored stone wall will lead to what is commonly classed as ‘rising damp’. Downpipes should be directed away from the building, ground levels round the perimeter should slope away where possible, and hard standing should be removed and replaced with a material that allows evaporation from the ground such as grass or gravel. Some aspects of drainage are relatively cheap to address, but can make a massive difference to the dryness of the property.
Another concept to consider when deciding which area of the building to prioritise remedial works on is that of the ‘weather wall’. As long as the hat of the building is well maintained, rain which falls straight down is not too liable to penetrate the fabric of the building, even when the pointing is poorly done. Wind driven rain is much more likely to penetrate and saturate a wall. The wall(s) that take the brunt of the prevailing wind and therefore the wind driven rain are referred to as the ‘weather walls’. After the hat and the boots, they are the most important area of the building to address.
Internally, so long as the weatherproof shell of the building is functioning correctly, damp issues can by and large be managed by the intelligent use of heating and air flow. This has been discussed at more length here.