Crack in blockwork between extension and existing house

Discussion in 'Builders' Talk' started by kevforumnew, Jun 13, 2020.

  1. kevforumnew

    kevforumnew New Member

    I had a two story extension built a few years ago, upstairs is still bare block and i have noticed a crack/ gap from the ceiling to floor mostly in the mortar (and 1 block). the crack/ gap is between the extension and the existing house

    I noticed it when the extension was first built and was advised was due to the mortar drying out and settlement.

    The white spots is filler to see if it crack/ separates.
    IMG_02 shows a £1 can partially fit

    Im not sure if the gap has slightly widened (maybe paranoia) but at the top of the wall the gap is 5 to 6mm at the bottom the gap is about 3mm, is this normal?

    Attached Files:

    Last edited: Jun 13, 2020
  2. Abrickie

    Abrickie Screwfix Select

    The mortar was always going to crack on that vertical joint, it’s just too long. Silicon/mastic is your friend for a construction joint .
  3. kevforumnew

    kevforumnew New Member

    Thanks, it's 6mm away at the top and 3mm at the bottom, anything to be concerned about?

    Is a 6mm gap / crack acceptable there?
  4. Severntrent

    Severntrent Screwfix Select

    What do you mean a construction joint? surely its just a bog standard wall tying into another wall (hopefully with starter ties) normally finished off with plaster so mastic would not have been appropriate.
  5. Nev Hope

    Nev Hope Active Member

    @Abrickie you’ve been reading too many insurance schedules, no one else calls that a construction joint lol.
    @Severntrent why assume wet plaster ? Dot and dab is more common

    Anyway to answer the OPs question, drying out and settlement cracking are the norm with such a joint, hence the reason the reason the manufacturers of wall starters recommend polymer based sealants or pre compressed sealing strips for the external skin. A 6mm gap is not a cause for concern.
  6. kevforumnew

    kevforumnew New Member

    Great thanks!
    I am wanting some structural work doing in the old part of the house in a couple of month so will get a structural engineer to check the wall aswell but it gives me a bit of piece of mind till then.

    I will still keep an eye on it aswell .
  7. Severntrent

    Severntrent Screwfix Select

    @Severntrent why assume wet plaster ? Dot and dab is more common

    Cos I'm old school
    Astramax likes this.

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