Client: Educational Institution
Our client, a school in Westminster, London, contacted Timberwise to conduct a thorough survey to determine the extent of issues associated with rising and penetrating damp, and wood rot decay. Our survey was limited to specific areas of the building we were asked to inspect, which was predominately the music department. This property was a large semi-detached school building of brick construction, built in the 1900s, and was both occupied and furnished at the time of our inspection. Weather conditions on the day of the survey were dry and sunny.
Challenges
Our survey access was restricted in most parts of the school due to the fitted units, tiled walls, furniture, stored items, and floor coverings. We also had to be mindful of other people in the building, such as teachers, students, and other members of staff. The third-floor science room was limited to only an internal inspection due to a lack of external access. All other floors were either easily accessible or could be viewed from the ground floor.
External ground levels at the front were approximately 150mm-200mm higher than the internal solid concrete floor, increasing the risk of moisture ingress.
Observations
First, we completed an external observation of the property. Due to the property’s age, we correctly surmised that it had a slate damp proof course installed.
We noted that all of the window frames were of timber constructions. Almost all of the frames were in reasonable condition, though they were in need of general maintenance and painting.
We noted that the external ground to the front set was approximately 150mm to 200mm higher than the internal solid concrete floor, which could result in penetrating dampness. The downpipes and guttering were made of cast iron; we noted water staining to the outside of some of them, indicating that possible splits and cracks have occurred over time, which has allowed rainwater to travel down the ace of the brick walls.
For the external brick and pointing, we noted on the front elevation there were signs of frost damage to the face of the bricks and washed out defective pointing, all which can result in damp penetration. We were also informed by the occupants that the property has a history of flooding from ground and rainwater ingress via inspection chambers and door openings.
Moving into the property, we recorded rising and penetrating damp in multiple locations, including the stairwell area and multiple rooms in the music department, which included the ensemble room, director’s room, music room, music technology room, and adjoining corridors. We had noted that the timber of the lower ground floor level, there were no signs of an active woodworm infestation, nor any wet or dry rot at the time of the inspection.
We noted particularly high levels of damp in the stairwell, with it registering between 31 and 37%, meaning it was highly likely to develop fungal decay in these areas. Levels of damp reaching to around 21% were also recorded in the music technology room. High levels of damp were recorded in the music technology room, with some areas exceeding 50%.
High levels of damp were detected in patches in the ensemble room and corridor and other rooms, with some readings hitting 100%, meaning the walls were saturated. Internal walls showed evidence of soluble hygroscopic salts (chlorides and nitrates) deposited in the fabric and plaster.
For the third floor science room, there was noticeable water ingress and plaster staining to the wall plaster on the front elevation wall. At the time of the inspection, we could not confirm where the moisture levels had come from directly, but assumed it was more than likely due to external defects that we could not assess when completing the external observation of the property.
While no active wood rot or wood-boring insects were found in the timbers, skirting boards were cracked and split, requiring replacement during our proposed damp proofing works.
Solutions
After our inspection, we outlined our recommendations to the client. To prepare the areas outlined for treatment, we would use dust sheets for stored items and furniture, and use hardboard taped to the floors to protect them. We will apply a polythene sheeting over any large free-standing items in designated work areas.
Where the original plaster extends below the floor slab, this will be raked out, cleaned and the void filled to floor level. A vapour proof slurry coating will then be applied to the wall-floor intersection up to the DPC installation level. This jointing technique will considerably reduce moisture vapour condensing on both the underside of plasterwork and the rear surfaces of skirting boards, extending their life span. Exposed masonry will be also covered with two coats of waterproof slurry.
For damp proofing, we recommended to the client the installation of a horizontal DryTek DPC System which will be done by drilling holes into the mortar joints and injecting chemical barriers. We also proposed installing vertical barriers to prevent any damp penetration abridgement from the adjoining masonry.
To finish off the resulting work, we proposed hacking off and removing existing salt-contaminated plaster, before re-plastering with a salt-retardant specification to heights of 1 to 1.2 metres, where applicable. We will also organise the complete removal of resultant debris and waste from the site.
Results
We identified all the defective areas through instrumental moisture readings using a Protimeter Surveymaster, which was non-intrusive and didn’t cause damage to the property. As we only conducted the survey at this moment in time, we have given the client a comprehensive specification as outlined above in our recommended solutions, which detail remedial works that will combat and prevent future instances of rising damp and penetrating moisture. Our suggestions will provide the client with a long-term 20-year guarantee for the chemical injection and finishing systems over 15 rooms in the property.
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