Lime Rendering / PlasteringMany older properties suffer from damp problems, cracking or hollow render and flaking paint. It can be difficult to pin down the causes and there is often conflicting advice to contend with even before taking the plunge with expensive repairs or damp treatment.
Before the twentieth century building techniques and materials were very different from those employed today. Traditional properties need to "breathe" to allow moisture inherent in a solid wall construction to evaporate from external stonework or render. Lime Putty was the base product widely used to produce mortar, plaster and limewash for traditional buildings. Lime putty mortars offer advantages over cement based mortars for external rendering of these properties, especially when decorated with a breathable paint such as limewash.
- Their porosity allows the structure to breathe
- They can accommodate general movement better
- Their self healing nature reduces cracking problems
In contrast to these breathable lime materials, too many traditional buildings are repaired and renovated using harder and impermeable materials designed for modern buildings of completely different construction methods.
The result is often worse dampness problems.
To manufacture lime putty, first limestone is burnt in a kiln to produce quicklime. The quicklime is then mixed with water to produce a boiling liquid which is passed through a sieve and then left to mature in a pit or tanks for a number of months. This process is called slaking and the resultant lime putty ends up the consistency of cream cheese.
The mature lime putty is then mixed with a sand to make a lime mortar. Coarse sands are typically used for building and pointing and finer sands for finer plastering. Animal hair is teased into the mixes for backing coats of plaster. The mixed lime mortars should be left to mature for a further week or two before use as this minimizes any tendancy for the mortar to shrink and crack during curing.
In particular, hard cement renders and many masonry paints fail to allow moisture that is continually being sucked up from the ground to evaporate easily to the outside. This may result in damp, cold walls, condensation, flaking paint, rotten skirting boards, joists and other timber fittings, increased heating bills and a never ending battle to hold back the dampness from the inside. Chemical damp course injections, tanking and even drylining are common prescriptions wherever the “professional” has failed to understand the basic requirements of a traditional property. In the worse case scenario the combination of sealing the external and internal walls leads to a dramatic rise in the moisture levels in the wall, causing severe damage to earth and timber framed structures