Property

Will a water-seal compound work on my gable wall?

Property Clinic: Your questions answered

‘If the moisture is entrapped then it will be necessary to expose the inner parts of the wall’

Thu Oct 12 2017 - 06:00

My house is 102 years-old, has two storeys and a basement. In 2009 I reroofed it, and plastered the gable wall.

Unfortunately, it was plastered with a cement and sand mix. I now have damp on the floor of my attic, on one of the main timber beams, and on my two downstairs bedrooms.

The damp is only there in the past six or seven years. This year I got a building surveyor to check it out. I am only doing the recommended, remedial works to the outside of the building.

I have read up a bit about the products that shouldn't be used on old buildings. Among other works, my surveyor has recommended painting the gable wall with a water-seal compound. I questioned him about its suitability and his answer was, "You must stop the water coming in".

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As this job is costing a lot of money, I need to be certain the water-seal compound is not going to cause more problems, and more expense later.

Is it okay in this instance to use a water-seal compound on my wall?

Your house was built around 1915 and may well be Edwardian style. Typically a variety of materials were used at the time including stone, brick, renders and brick jointing with lime mortar. You provide no more detail of the construction, so I assume the house was built using traditional breathable materials. The works were carried out in 2009 to plaster the gable wall in sand and cement and dampness is now present internally. Were you aware of the source of the dampness before, and was it in the wall? The addition of a hard cement will prevent the wall drying and this may have affected the internal areas you refer.

Recently, I inspected a 150 year-old stone cottage that was riddled with dampness internally. It had hard cement applied in the 1980s. This was removed and replaced with a lime plaster that proved very successful. It was labour intensive and expensive, and economically this is not always an option. If your house is brick then removing hard cement can damage the brickwork.

If the moisture is entrapped then it will be necessary to expose the inner parts of the wall to ventilate and dry out the damp. Some older buildings renovated today are internally insulated with dry lining. It is important to leave a ventilated gap between the original wall and new lining system. This will allow any residual moisture to breathe and hopefully dissipate, and at the very least enable you to manage the problem. A “dew point” analysis should be considered to rule out the risk of interstitial condensation.

In your situation, I would avoid the use of any water-sealant compound. You should go back to your surveyor and ask them to review the matter in light of our correspondence. Alternatively you could speak to the Society of Chartered Surveyors Ireland (scsi.ie) and ask to speak with the chair of the building surveying professional group who should be able to put you in touch with a reputable practitioner experienced with these types of buildings.

James Drew is a chartered building surveyor and member of the Society of Chartered Surveyors Ireland, scsi.ie

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