Penetrating damp can arise through a variety of causes such as driving rain, high external ground levels, bridged damp proof courses and defective rainwater goods. Remedies can vary.
Rising Damp Defective Rainwater Goods
Some issues such as issues with rainwater goods require the source of the water to be addressed and it is then a question of the extent of damage internally and whether it is viable to allow to dry down over time, or whether plaster is removed and reinstated. To allow rapid reinstatement, this can include the application of a membrane system to the wall before new plaster is installed, such that the internal finishes are protected and the structure can dry outward of its own accord.
Chimney (Salt) Damp Treatment
A classically mistaken interpretation of issue is dampness upon a chimney breast. If at some point rainwater is able to access a chimney flue and can drain down this, that water will run across and through any soot which lines the flue.
That water will leach salts from the soot, the salts are dissolved by the water and carried in solution. If that water is able to soak into masonry and eventually to direct applied plaster on the masonry, some of that water will evaporate which means that it changes from a liquid to vapour which is a gas.
Salts cannot change into a gas and will be deposited at the surface of the plaster. Chimney flue salts are hygroscopic, which means that they are capable of absorbing moisture from the air (the extent of vapour inoccupied properties varies but there will always be some degree of moisture present in the air.
Damp patches on a chimney breast can give the appreance of a leaking chimney, and the roofer may get called back when it looks like they've not correctly repaired to stack. It can just be hygroscopic salt contamination absorbing moisture from the air.
Typically that plaster has to be removed and reinstated internal of a membrane which isolates new finishes from the salt contaminated masonry.
Lorem Trace has completed over 50,000 surveys and 18,000 projects in our (nesrly) 50 years of trading.
Lorem Trace's principal damp and timber Surveyor is Chartered and a Member of the Royal Institute of Chartered Surveyors. There are few MRICS Surveyors specialising solely in problems of dampness within buildings.
Award Winning, Examiners
Directors won the annual award given to the candidate achieving highest marks in the Property Care Association examinations for damp proofing and timber treatments - CSTDB. One Director now acts as an examiner for that qualification.
Issues associated with driving rain can cause dampness internally, or even in extreme cases the penetration of liquid water to the interior. Often there are issues associated with pointing but typically in our experience there may also be pathways into cavities or solid walls through gaps between glazing frames and abutting masonry.
We've seen some really interesting examples of issues caused by driving rain, one was a set of timber glazed doors with glass panels to either side. The homeowner found puddles on the floor internally after heavy driving rain (property very exposed to weather).
All the doors were replaced at a cost of several thousand pounds, but with a better seal detail beneath (it was thought water was coming in under the doors) but the issue returned. We established that water was getting past the seals around the edge of glass, then running through tongue and groove joints in the panels beneath to access the interior. All that was required was to seal around the glass.
We can and have in the past applied cavity membranes to walls externally, which are rendered, but in most cases this is not necessary.
We do not undertake a great deal of work to combat issues of condensation, but we understand the mechanisms and remedial works associated with this issue. We do also have the equipment for data logger condensation investigations which record air/surface temperatures and relative humidity within a space over time (usually one week), allowing assessment of conditions over that timeframe, principally at different times of day, which is advantageous versus a snapshot inspection undertaken during the day for example.
The typical options to address condensation issues are - reduce vapour production (put less water into the air), warm surfaces (assuming not interstitial condensation) via heating or the addition of insulation, or deal with vapour via ventilation, or in theory dehumidification can be used but rarely is.
Ventilation is a big subject area in it's own right, but our general approaches/opinions are - deal with moisture at source, so continuous running fans with humidistat function in wet rooms (kitchens and bathrooms). Positive Input Ventilation (PIV) systems are like forcing the windows to be left open, and whilst they can be effective, in no way would I want one of these units in my own house, so I wouldn't recommend it to our clients. Readily available and easy to install heat recovery fans are preferable in achieving air exchange with outside, but without making a property colder.