Cracks in Front Wall

11 Jan 2004
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United Kingdom

Bit of advice needed, please.

I am decorating a front bedroom. Before the extension was built, this front bedroom was part of the original master bedroom, along with the next door room.

Basically, they took out the original picture window and replaced it with two smaller units separated by some new block work and split the room in two with a stud wall.

Below the bedrooms is the lounge with a picture window.

Outside, the front wall is rendered above the lounge window.

For a good while we have had cracks in the render: one vertically down the middle and some running horizontally.

They were always there and have been patched up over the years but return.

I'm not sure if the filler drops out with time and weather or else there is still movement?

When we bought the house in 1999, we had a survey that said there was historic slippage (the house is built on clay) and the front of the house had sunk slightly.

Back to the issue. Having stripped the wallpaper (hung in 1998, according to the notes below the wallpaper), there were cracks in the plaster. Having scraped out the plaster, it can be seen that there are cracks right through the cinder blocks (a wallpaper scraper disappears into the crack).

This crack inside coincides with the vertical crack in the render on the outside wall.

There is another crack underneath the LHS of the front window, and another underneath the LHS of the side window, pictures below.

Just trying to get a handle on whether this is a serious problem, ie may require underpinning at the front, stitching of the cracks or whether we can just fill the cracks with fillers/ plaster and move on?

Outside front wall: will get a better shot in daylight

Inside front wall

Under LHS of front window

To the RHS of front window

Side window

Under side window
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Internally, being vertical, relatively even and with no horizontal misalignment, suggests thermal/shrinkage cracking. However the external pattern suggests some deflection above the GF window. May be both.

Either way it does not appear to be foundation related and not "serious". It could most likely be remedied with some helifix bars and designed to form a beam not just as crack stitching.

A structural engineer could likely sort this out, or a specialist contractor such as Bersche-Rolt - Specialists in Structural Repairs (

Thanks very much for explaining that, much appreciated.
I have seen cracking due to thermal movement, but never thought this could causing cracking right the way through blockwork.

I'm relieved that looks like it can be remedied without major disruption!
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Yes when they crack it's right through. Whilst that there is extreme - there would normally be just one or two cracks far apart not near, but in extreme cases like this there can be several cracks close together.

At a guess that rendered wall looks like its been getting quite wet, so the cavity could be going through some rapid temperature and humidity changes, which those soft blocks can't cope with.
When you say soft, they're not Thermalite, but I guess in the range of blocks, they're not hard, either!
They appear to be soft lightweight concrete. A bit like the old clinker blocks, so relatively fragile.
Thanks very much, Woody.

Off to find a structural engineer......:)

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