What we do Building Preservation
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Building Preservation

Preservation. (noun) - "the act of keeping something as it is, esp. in order to prevent it from decaying or to protect it from being damaged or destroyed."

For over 40 years K.T. Preservation have played a key role in preserving architecture and history across the south of England -

Other fundamental services we provide include:

  • Wall-tie Replacements
  • Plastering (Internal & External)
  • Traditional Lime Plastering / Rendering (Internal & External)
  • Re-pointing Brickwork (Traditional & Modern)
  • Air-brick Replacements / Ventilation Installation
  • French Drainage Installation
  • Condensation Control
  • Insulation to Roof Spaces
  • Minor Timber Repairs/Replacements


Most, if not a large number of these are self-explanatory and frequently they get highlighted in our report after conducting the survey. Some are more critical than others as they act as the first line of defence against damp and timber decay developing in the property and would be prioritised before any proposed remedial action be taken inside, depending on the situation, as there is no one scenario the same.

What are wall-ties?

Wall-ties are exactly what they are named, an invisible tie situated in the cavity of a wall that bond the internal and external leaves of a wall together.

The year 1805 appears to be the first known mention of cavity walls, in William Atkinson’s book; "Views of Picturesque Cottages with Plans." He describes that you save the cost of materials with the construction of a hollow wall instead of a completely solid one and further suggesting an advantage that, the trapped air would act as an insulating layer. However cavity wall construction didn't fully evolve until the end of the 19th century, although it was widely incorporated during the 1920's building boom it was not until after World War II from 1945, that it became fundamentally standard throughout the building industry. 

The universal and most frequently used were made of mild steel and in the very early days they either were left untreated or had a bitumen coating and it wasn't until the early 1930's that a zinc coating or galvanising became conventional.

Wall-tie corrosion was first observed in the '60s and initial investigations signaled the construction industry to a potentially profound problem of massive proportions however it wasn't until 1981 until the significance of the issue has been truly recognised.

The process occurs when metallic oxide (rust) forms around the wall-ties which causes expansion in the mortar bed on which they are laid, most often in the outer leaf, which in turn gives way to the classic symptoms that can be seen, such as fairly obvious horizontal / vertical cracking and bulging / sagging of the brickwork, especially around lintels. If left, they will cause tremendous structural damage and subsequently colossal repair costs.

Statistics from the 1986 Survey of English houses published by HMSO indicated that a total of 11.3 million houses were built between 1919 and 1986, and of these 906,000 now require repairs to the wall structure.

There is a life expectancy on wall-ties in properties built up until 1981; construction pre 1945 is unknown, those built between 1945 and 1964 have an average life expectancy of 35 years and the average life expectancy of wall-ties in properties built between 1964 and 1981 is 27 years. 

The only certainty we have is that ALL mild steel wall-ties will ultimately corrode, the question is when?

The circumstances affecting corrosion are due to several factors and the principle determinants are:

  • Porosity of brickwork
  • Quality of mortar
  • Chemical action within the mortar
  • Location of property
  • Driving rain, weathering of facades
  • Poor maintenance
  • Poor design and construction problems

Whatever the cause of wall-tie failure, it is important that the problem is resolved quickly and correctly to avoid serious structural damage and prevent the danger of collapse.

(Below is the installation of stainless-steel finned helical remedial wall-ties at a property in Salisbury)

Sub-Floor Ventilation

The importance of ventilation in buildings, especially regarding in-situ timbers, was seen to have started being mentioned as far back as 1815 as it was first perceived to have prevented the growth of the Dry Rot fungus (Serpula Lacrymans), because in the early 19th century, there was no general concurrence that Dry Rot needed water to develop and flourish.

Throughout the 19th Century the ideas around ventilation and hygiene had lead to the result that it was shown to dispel condensation and also for example, in 1832 we can find a man called Henry Belinaye recommending that building laws 'assure free ventilation', thus it was made a common thought around this era, for both the occupants and the house:

"A draughty building is a healthy building."

The period witnessed a steep increase in population, one that doubled from 1801 - 1851 and which was to double again around World War I. This surge in population was assisted by the industrial revolution and was absorbed mainly in the growing towns, resulting in overcrowding, lack of sanitation and serious cholera outbreaks. The London Building Act of 1774 was a foundation for future reform but it relied principally on fire control which had been the issue of the last century, consequently the act made no controls which related to matters of health. Demand for change grew and when calls for a national Building Act in 1841 came around, it was natural, to find the 1774 Building Act being used as a model.

On the 29th January 1841, we see for the first time a specific recommendation for air-bricks in buildings, in a bill put forth by Lord Normanby, named - Bill: for The Better Drainage and Improvement of Buildings in Large Towns and Cities. 

Clause 24 stated that: 

Level of ground floor to be 18" above footway or road adjoining, with air-brick in front and back wall, 9" below level of floor."

These ventilating 'air-bricks' are the foundation for the ones that we know of today and appear to have been patented during the first half of the 19th century, although they were not fully implemented until the later model by-laws in 1877. 

We're often privy to conduct surveys in period properties, most often built with timber flooring and with the original flooring usually still in place, therefore if any defects are to be found with the sub-floor ventilation it's important it be noted and remedied as it can lead to unwarranted future problems that could become quite uneconomical.

(Below - an example of replacing air-bricks. In this interesting case high outside ground levels and overgrown shrubbery had blocked the existing metal air-vents causing them to suffer corrosion and damage, to which also the ground had bridged the slate damp proof course to the point that it was not visible. We noted historic attempts to install a remedial chemical damp proof course externally however the problem would have simply been solved with our findings and suggestions. We excavated and drew back the ground level, found and checked the existing slate damp proof course, repairing areas that had fragmented although it was in good condition and installed new air-bricks with shuttering and drainage as there was a new pathway to be constructed around the property.)

See our Timber Treatment for further information on timber decay.

Have a look at our case studies for a more detailed look at our past contracts and if you have any questions, or are interested in having a survey in relation to anything that has been mentioned above do not hesitate to contact us.

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