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The damp wall and the mini-swimming pool

October 24, 2010

Three years ago I was asked to take a look at a property, which the new owner said had a major damp problem. Upon arrival and being directed to the rear reception room of a Victorian mid-terrace house, the dampness was plain to see.

Damp along party wall of rear reception room

To some the first reaction would be to call in the “specialists” but we all know where that one ends up. To solve this problem requires logic not magic! 

In a previous post entitled Rising damp is NOT a source of dampness, I mentioned G Hunt who wrote ”the source of dampness is often very difficult to track down but surprisingly easy to resolve”. Well the following case was a perfect example of this rule.

Again, I started by asking myself the 2 basic questions; What’s the Source of dampness? and what are the Damp pathways? 

It seemed clear from the outset that the most likely DAMP PATHWAY was the earth beneath the timber floor and the gypsum plaster was just sucking the moisture up the wall. This is clear from the pattern of dampness on the photo. Also look carefully at the height of the damp stain and where the highest part of the dampness is to be found. It’s towards the back wall near the curtains (left of photo). This will give us a clue as to where the wettest areas might be found and a pointer towards the Source of dampness.

To the unthinking believer, the fact that I didn’t immediately concluding that the wall had “Rising Damp” is heresy. The common belief is that a pattern of dampness such as that found on the photo is due to the failure of the damp proof course (DPC) and the porosity of masonry. All this will have been concluded from a few prods of the resistance meter.

However, Jeff Howell’s book The Rising Damp Myth has dispelled the notion that bricks will readily soak up large volumes of water. Moreover, in order for bricks to suck up any significant amounts of water, they need to be standing on saturated ground and if the ground is saturated the issue surely is the saturated ground and not the bricks.

Now what was less obvious was the exact SOURCE of dampness and to establish this we had to open up the floor…

Once the floor was exposed I noticed that the timber floor itself was not original, but of more interest was the height of soil. The damp earth was literally a few centimetres below the floor joists. This confirmed that the earth was an important Damp pathway.

The lower air brick was the entry point

My next thought was to look outside, but the back garden was almost completely covered with timber decking. If the source of the dampness was outside it would be under the decking…

Having emptied the back garden of decking the first clues as to the source of dampness became clear.

Below the very wet decking was an air brick, just visible in the photo (left) and below another air brick. But a few metres away was a flower bed which had been completely covered by the decking. Moreover, the perimeter of the flower bed had been defined by a single course of bricks.

It suddenly became very clear what was happening. The single course of bricks below the decking was acting as a dam, preventing surface water from running into the flower bed and draining away naturally.

Instead the flower bed’s brick boundary wall was in fact creating a mini swimming pool under the decking and as the water level rose (after rain), the surface water was just pouring in through the lower air brick. The water was then saturating the earth under the timber floor and the wall plaster was soaking up this moisture. The Complete Damp Pathway had been established and the Source of dampness was the poor surface water drainage under the decking.

I say again, if the “Rising Damp” diagnosis had been made, the wall would have been injected etc etc and the Source of dampness and the Damp pathway would still be very much in tact.

Remedial work simply involved removing the bricks around the flower bed to allow good surface water drainage and internally, lowering the soil levels against the party and rear walls below the timber floor. In addition the fireplace was opened up again and the dirt from the chimney flue was removed. The wall was left to dry out naturally overtime.

Job done it was now time for a hot mug of tea!

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From → 3. Dampness

One Comment
  1. I do accept as true with all of the ideas you have introduced on your post.
    They’re really convincing and can certainly work.

    Nonetheless, the posts are too brief for starters. May just you please extend them a little from next time?

    Thank you for the post.

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