Newspaper article The Journal (Newcastle, England)

Act Quickly to Tackle Cracks; House D O C to R with Peter Fall of Clear Building Survey: House Doctor Peter Fall Explains Why Walls Move Upwards

Newspaper article The Journal (Newcastle, England)

Act Quickly to Tackle Cracks; House D O C to R with Peter Fall of Clear Building Survey: House Doctor Peter Fall Explains Why Walls Move Upwards

Article excerpt

Byline: Peter Fall

I HAVE a confession. If I look at a property affected by cracking, my first thought is that it must be subsiding - one part dropping, leaving the other part behind.

If the cracking is to a particular pattern, I might consider horizontal movement. Only after I've exhausted these will I turn to cracks caused by one part of the building moving up and leaving the other part behind. Why? Well, it rarely happens. Or does it? There are two ways a building can be pushed upwards - and they aren't that rare. One is the effect of the soil expanding rather than shrinking and the other is the result of cavity wall tie corrosion.

Let's start with the soil problem. If the soil under a building is a particular type of clay, then its bulk will change with its moisture content. If there are large trees in the area, the moisture will be extracted from the soil by the roots. This causes the soil to shrink and any buildings will settle down on to the reduced bulk of the clay. The opposite happens when the soil becomes wet again. It expands and can push a building upwards. This soil recovery can be because the trees have been removed or that after a long dry spell we have a period of prolonged rainfall.

This upward movement is called heave and in some areas can be a common problem. Some parts of the North East are vulnerable but fortunately not too many. A defect that is more widespread is cavity wall tie corrosion.

If you have a house built 75 to 110 years ago, with a mortar that has black ash mixed in and is near to the coast, then it could be vulnerable. Homes older than this weren't built with cavity walls and houses built after the Second World War are not quite old enough.

The black ash is a bit aggressive, particularly when combined with salt-laden rain.

Older cavity wall ties are pieces of twisted steel strips built into each side of the cavity wall to stop the two leaves pulling apart. …

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