Flood Damage or Failed Damp Proof Course (Part 2)

So four weeks later, we returned to the property to undertake a further inspection and compare our findings to our initial report, provide a diagnosis and repair specification.

As mentioned in our first blog post (Part 1), the building displayed symptoms of a severe damp issue which appeared to be affecting the majority of original ground floor walls within the building.  The walls displayed symptoms of damp with spoiling and deterioration to the internal plaster and decor, accompanied by high moisture levels in the adjacent door casings, flooring and timber skirting boards.  A disruptive investigation to determine the moisture content of the masonry walls was undertaken, following which low readings were recorded at 5% total moisture content when tested with a calcium carbide meter.

My opinion following our initial visit was that although the walls displayed severe symptoms of damp which had previously been specified as a failed damp proof course by others was more than likely that damp observed was in fact a result of water escaping beneath the building a recent occurrence.  As previously mentioned the moisture content of the walls at 5% was low considering the evidence of severe spoiling and deterioration observed internally (see extract from BRE 245 below). Part of this 5% was also perceivable as salt contamination of the masonry due to the absence of a damp proof course when first constructed. The recent occurrence of flood water migrating through the structure will have moved hygroscopic salts in solution from the contaminated masonry into the new plaster.

The British Research Establishment Digest Paper 245, revised 1986 reports the following:

“To obtain more conclusive proof of the presence  of rising damp the most satisfactory approach currently available is to remove a small area of plaster and obtain samples from the mortar and bricks or blocks at some depth in the wall. 

From these samples an accurate measurement of the moisture content of the wall can be obtained, together with an indication of the influence of any hygroscopic salts that may be present.  The sampling technique creates a limited amount of dust and slight damage to decorations.  A wrong diagnosis could however lead to considerable unnecessary expenditure (in the installation of a replacement damp proof course if not needed). 

The moisture content of two components of the wall (mortar and bricks or blocks) will generally be different and it is the higher figure that must be considered.  If the found moisture content (MC) is less than 5% at the base it is unlikely that the wall is severely affected by rising damp”.

Experience has shown that some building materials possess an HMC (hygroscopic Moisture Content) of up to 5% even without the introduction of salts from external sources.

(Extract from BRE Paper 245)

The purpose of our second visit was to investigate the condition and moisture content of the walls following what was considered to be a further natural drying period based on our initial judgment.

A further visit was made to the property and where seen, there was no visual evidence of changes to the symptoms of damp from that of our initial visit however, when the walls and adjacent joinery where tested considerable changes in the moisture content of those materials was noted.

The moisture content of the timber skirting boards was noted to have reduced from that of our original inspection.  When tested the door casing leading into the front right reception room during our initial visit expressed moisture levels of 31.9% WMC (wood moisture content).  On our second visit the moisture content of the same door casing had reduced to 22.6%, evidence the timbers are drying.  Further readings were also taken from the timber skirting boards at exactly the same place as our initial visit, which again revealed evidence the skirting boards are drying with a moisture content reducing from 24.8% to 21.6% wood moisture content.

To further the inspection another calcium carbide test was taken from the same wall as previously tested approximate 1″ to the side of the original test hole, thus making the results as comparable as possible.  In addition, the exact same depth of test hole was also used for the extraction of the masonry sample.  It is most likely that due to the close proximity of the original test hole that the same brick was tested.

Our original inspection revealed the moisture content of the masonry on our first inspection was approximately 4.8 – 5% total moisture content, this includes hygroscopic moisture, free moisture and contamination. Our second visit four weeks later revealed moisture levels of 1.1% total moisture content. Again our results show a considerable reduction in the amount of moisture present within the masonry. In addition 1% total moisture content is the approximate estimated moisture content of these bricks in their dry condition with no contamination (similar to the moisture levels recorded to the wall absent from evidence of damp – see 1st blog post).

Moisture content of the door casing – Visit 1	Moisture content of the door casing 4 weeks later – Visit 2
Moisture content of the skirting boards – Visit 1	Moisture content of the skirting boards 4 weeks later – Visit 2

Calcium carbide test 5% – Visit 1	Calcium carbide test 1.1% 4 weeks later – Visit 2

Our findings during our second inspection confirm our suspicions from our first visit that the walls and adjacent joinery articles are drying.  The moisture levels recorded in our second visit of slightly over 1% total moisture content would not be sufficient to cause spoiling and deterioration to the internal finishes as seen, as previously mentioned 1% total moisture content is the estimated moisture content of these bricks in their dry state.

In addition, readings taken from the masonry again would not indicate the damp proof course has failed over a period of time. Rising damp is progressive and continuous, fluctuation is only likely to occur between periods of dryer weather however it would not be expected that the moisture content of the wall would fluctuate within the region of 4% as seen. It should also be mentioned only a period of weeks elapsed between our visits over the winter months when ground water levels are perceived to be at their highest. Therefore drying of the walls can only be perceived as excessive moisture introduced into the walls due to the recent flood beneath the building caused by the defective water service.

Therefore, our diagnosis is the higher moisture levels recorded during our first visit were as a result of moisture migrating into the structure caused by the escape of water beneath the building and the reduced moisture levels during our second visit were confirmation of the walls and adjacent finishes are drying naturally after the defect had been repaired.

As previously mentioned, chemical damp proof courses are designed to reduce capillary moisture under normal circumstances and in the event of severe amounts of water escaping beneath the building over a short period of time this will inevitably induce stress upon the chemical damp proof course and its failure.

Whilst theoretically rising damp has occurred defined as the progressive upward movement of moisture within the structure of the building, caused by the damp proof course failing due to the stresses imposed upon it. However, under normal circumstances this retrofit damp proof course installation would have provided adequate protection to the building as it had done prior to the flood, under normal conditions. Inevitably therefore we can safely assume with our findings that excessive amounts of water escaping the building have caused the scenario to occur which would be outside the level of protection a chemical system could provide.

The insurers have accepted our report and findings and we have now produced a specification for repairing the building and await their decision. Good news for the client as now the expense of the repair will be covered by the insurers.

To date the quantity of water which had escaped beneath the building is still unknown, however is perceived to be thousands of litres in a very short space of time considering the structural impact on the building causing the floors to move and fracture.

When in need of expert advice for damp diagnosis and repair don’t hesitate to ask, call “Yorkshires Leading Damp & Timber Specialists” Dryfix Preservation Ltd. We are full members of the Property Care Association, our surveyors are fully qualified and all our workforce are Qualified remedial Technicians.

To find out more about our company, our accreditation’s and understand what all the association badges mean visit our accreditation’s page on the website or read our blog article members of the associations that matter.

Many thanks

Russell Rafton

C.S.R.T / I.S.S.E

Dryfix Preservation Surveyor

http://www.dryfix.net