The Conservation Project

When surveying an older property and specifying the necessary repairs, an initial survey would identify the obvious causes of damp problems such as the ground levels, roof problems, joinery decay, external finishes etc.

These would then be repaired and the building allowed to dry, allowing at least a month for every inch thickness of masonry, or by speeding up the process a little by gently heating and ventilating but not too quickly, as rapid drying could cause some cracking.

Plaster finishes could then be checked and monitored to see if damp returns. Given that rising damp can be seasonal this could take some years.

Walls can be checked for salts. If salts are found above the level of the outside ground then you can be reasonably sure that damp has risen up the walls at some time.

If the rising damp is as a result of excessive ground water at the base of the wall, then external drainage can be installed and or landscaping improved, taking care not to disturb or undermine what could be very shallow footings.

If the damp is cured but salts remain a problem, then sacrificial lime mortars or a poultice can be applied. However, if the moisture movement is cured, salts are unlikely to be drawn into the plaster, as they will for the most part only move in solution apart from high concentrations of deliquescent salts.

The reality is that all the above work can only apply to a conservation project. The work is normally driven by the purchase or inheritance of a house. Potential owners normally have financial and time constraints. If the problems with damp cannot be assessed and a cost for repairs given prior to purchase, it is likely that the sale of the house will fall through.

If houses do not sell they will not be looked after and will continue to suffer from ongoing damp and decay.

If an old property is surveyed by a competent CSRT or Chartered Surveyor and is found to be suffering from the effects of damp, then all potential causes should be checked such as roof, rainwater goods, high ground levels, external finishes etc.

The extent of the damp should be plotted by use of a moisture meter. Carbide meter tests on samples from within the wall can confirm the presence of moisture.

The walls should then be analysed at varying heights for salts. A check sample should be taken from well above the potential rising damp area to ensure that salts were not built into the structure in earth based mortars, cob etc.

If Sulphates, Nitrates or Chlorides are found to excessive levels in a band above floor level then that would be indicative of a rising damp problem.

If the outside ground level is not high and all other potential problems are investigated and ground levels cannot be reduced, then the problem will be ongoing.

If the damp cannot be cured then the wall is not suitable for lime plastering. No amount of breathing plaster will cure a damp problem if the building does not have open fires, draughty windows and doors and a limecrete, earth or timber floor.

Lime mortar plaster may well be less prone to damage from salts and damp, but it is unlikely to cure the problem and could become damp, stained and affected by salts.

If the building was built with a damp proof course, the installation of a new damp proof course will reduce moisture rising in the wall, but it is unlikely to reduce it enough for the use of lime mortar plaster.

Should the potential owner accept the financial risk and disruption if the damp reappears and spoils the walls? They should at least be made aware of the risks by the building professionals and given all of the options.
The Building Lime Company a division of LSE sells lime plasters and promotes their use for all traditionally built houses, but not on damp walls.

LSE have been involved with a large number of properties that have been re plastered with Lime mortar over damp walls, in some cases by market leading conservation practitioners and specified by leading conservation architects. The

walls have become so damp after a short period of time that the building work could not be completed. The lime mortar has had to be removed and replaced with a Ventilated Plaster Lath, at great expense and distress to the owner of the property.

Historically, houses were lined with timber wainscoting (a stud work on the wall with vertical boarding over) when they became damp. Grander houses had internal stud work and lath linings or hessian stretched over timber and then papered. We have even seen examples of timber lining covered with tin sheeting and wall papered. Timber linings will decay if they are not correctly detailed and ventilated.