Dry Stone Walls / Mortared Walls

Ivor Scott first started learning about stone walls when he was a teenager, a few years ago. Walls are a visible and very important feature on the hill farms of his native Scottish borders. They are still maintained as boundaries and enclosures for sheep and cattle on the hills and pastures. Coming from a family with ties to farming, when the opportunity came to learn how to build with stone, Ivor jumped at the chance.

Dry stone walls are not just important for farmers. They also provide a range of habitat for a wide variety of animals. While a new or well-maintained wall will provide huge amounts of shelter and living space for invertebrates and other small creatures, an older wall can provide nesting and living space for birds and mammals up to the size of stoats and weasels. Rare species such as newts find dry stone walls near water the ideal place to live as they can squeeze in between stones and feel a solid surface above and below them, which is ideal habitat for newts.

Walls can, of course, be built using mortar where this is appropriate or desired. In the 20th century, cement-based mortars rapidly replaced the lime mortars that had been used in building from Roman times. Cement was perceived to offer advantages in giving more rapid setting and strength to stone and brickwork. However, these advantages also came with serious drawbacks. The main difference between cement mortar and lime mortar is that the former is waterproof. Given that many building stones are porous sedimentary stone, this has often caused rapid erosion of the building stone.

Without getting too technical, these problems can be overcome by considering the use of appropriate materials in construction. The general rule in constructing a stone wall is now acknowledged that the mortar used should be both porous and softer than the building stone. If the mortar is waterproof and the wall gets wet, as it often does in this country, then water that gets into the stone can only come out again through the stone. Over time, this repeated wetting and drying cycle results in the movement of salts in the stone to the surface from inside the stone itself. These salts are themselves the binding agent that keeps the grains of sand together, forming the hard stone.  The stone surface then becomes brittle, cracks and flakes away, eroding rapidly in some cases.

Mortar was originally designed to be sacrificial; that it should take the brunt of the wetting and drying cycles and that it should be replaced by repointing between the stones when necessary, sometimes after many years. Appropriate mortar can increase the working life of stonework and buildings by many years.

If you have walls that are showing signs of wear and tear, with stones becoming loose, or pointing starting to fall out, why not have this looked at by an expert who can suggest appropriate repair methods.

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