When should I worry about cracks in my wall?

21 Oct 2003
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United Kingdom
This is the gable end wall of my house. We moved in about 8 years ago. The was a thin crack running down the wall of the upstairs bedroom. I cut back a little either side of the crack and filled. The crack has gradually reapeared.

The crack obviously follows the motar joints of the blockwork as it steps down the wall. It doesn't continue in to the living room below. Over the last year, other hairline cracks have appeared in the wall. ( the main crack being 1 to 2mm wide). I've just also noticed a 'step' in the plaster no more than 1-2 mm betwen either side of the worst part of the crack.

My question is who should I get in ?
Plasters to cut back plaster and replaster or a structural engineer incase it is structural :eek:
Would a plasterer let me know how serious it is?
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I would only worry if it was a sudden crack of greater than 10mm, or if the crack got progressively wider over a period of 1-2 years - again upto 10mm. In addition, there would have to be corresponding cracks externaly too

Buildings will move, and when a crack appears in plaster it it will most likely keep reappearing despite your attepts to fill it. It only becomes an issue if it keeps getting wider, as then there is continuing movement.

An engineer will cost you in excess of £500 and may well arrange further tests (drainage and ground) for completeness with even more cost. But this may be wasted money at this stage.

A plasterer will not "let you know how serious it is" - that is unless he is a surveyor or engineer doing plastering on his days off and is qualified in these matters
2 ways you can the repair the crack but first you have to establish if the block work/mortar is also cracked underneath. Put your finger firmly over the crack & tap one side of the wall with a light hammer, if you can’t feel any differential movement between the 2 sides of the crack, it’s superficial. If you can feel the one side of the crack moving independently of the other, it’s almost certain that the blockwork has cracked underneath.

Superficial cracks can be sealed by raking out & filling with a flexible filler or you could tape over with glass fibre repair tape & skim over the area but this works best if your skimming the entire wall.

I suspect your crack is in the second category, & the best way to do this is to remove the plaster right back to the blockwork for 100 – 150mm ether side of the full length + of the crack (wider if it’s a serious crack); leave a very rough edge to plaster up to or a new crack could appear along the join edge! Fix a 200mm strip of SS reinforcing steel mesh over the crack with galvanised nails, re-render to around 2-3mm below the surrounding area & then either re-plaster the repair level yourself or get someone in to do it for you.

Houses move around all the time (more so in the first 5-10 years) so there is no guarantee they won’t re-appear again but I’ve used both methods to repair some quiet serious older cracks on my 60’s house & they have not yet reappeared after more than 2 ½ years.

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