Internal cracks around lintel

3 Mar 2015
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United Kingdom

We have a 1960's semi, been in 18 months. Have noticed over the last 12 months (since a repaint) that there are hairline cracks (you have to squint to see them on the photos) around each end of a boot lintel on the inside wall. The window recess is 5 ft wide, and is an upstairs bedroom window on a south facing gable end, with cavity walls. The gable covers this bedroom and the bathroom next to it, so the window does not sit centrally under the gable.

I've read about boot lintels rolling due to only being held by the inner leaf, could this be what I'm looking at here? There are no signs of cracks externally in the same place having hung out of the window and had a look. The dining room window, which is the same size and directly below this room is NOT showing any sort of cracks, having recently re-papered and taken back to plaster before xmas.

Some other areas on this particular south facing wall have already been attributed to thermal expansion by the surveyor prior to house purchase.

Should I just rake out and fill with clear silicone, or do I need someone in for a proper look? (First house purchase and not massively clued up on cracks)

Any replies greatly appreciated....

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renton2015, hi.

Firstly welcome to the board, there are thousands of really good bits of FREE building information on here, should you need it?

As for the really small hairline cracks you have around the upper bedroom .plasterwork, they are difficult to see? in My Opinion the cracks have been induced by thermal and moisture movement.

The Concrete lintel is expanding and contracting at a completely different rate to the brickwork or block work that comprise the main wall in which sits the Concrete lintel.

It is all down to the Co-Efficient of Thermal Expansion of the two entirely differing materials.

As for repair? suggest an inverted VEE shaped cut in the crack, in-filled with a suitable filler, sanded off, then re-filled, to be sanded off again, followed by decoration.

Hope this post has been of some assistance?


Thanks for that - I was hoping it wouldn't be anything too serious. This room is due a proper decoration in the summer, after the quick colour change after moving in, so will to a proper repair job as advised :)

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