Advice: Bay window cracks in window reveal - structural or heat related?

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Hi guys,

I'm just looking for some advice/insight, any help much appreciated.

I've just purchased a property, and on my first visit since getting the keys, I found some worrying cracks in the plaster that somehow the surveyor missed. The cracks are on the internal Bay Window reveal (see images). They're diagonal, hairline, 1mm or less.

It should be noted there's an external stepped-crack which has been blamed on a previous uPVC window replacement. That external crack is about to be repaired with Helibar (and is 2-3mm gap). The cracks in the plaster are on the same side of the bay window as the external crack.

The surveyor suggests the cracks I found are nothing to worry about and are due to heat expansion/contraction. He suggests raking them out, and refilling, but the the plaster has blown between two of the internal cracks (they're now lipped cracks) - so obviously require a more comprehensive fix, which makes me wonder if there's more to it..

So, before I call in a Structural Engineer to look at it..

* Have you seen this before? (i can't find other examples on the web that look like the internal cracking)

* Because of the stepped crack outside, could the internal cracks be a possible sign of subsidence and not simply heat related?

* Is it possible that water has leaked through the external crack and is the cause cause of the blown plaster?

* If the plaster is removed/repaired will the cracks simply reappear due to heat? If so, is there a way to prevent this?


Any response is appreciated, any advice would be great.

L
 

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Have the windows now got proper support columns to hold the bay roof up? Helibar in the wall won't compensate for those being missing-it will compensate for no lintel above the opening
Is the bay original or is it an add-on?
Those cracks seem to indicate that the bay has sunk relative to the house. Quite common on older houses (where bays were added after building) to find not much foundation under the bay- might be worth digging a test hole to see how deep the founds are on the bay.
Not a major job to rectify...depending what ground you're on a couple of wind in piles would sort it out. Or rebuild the bay wouldn't cost a fortune
 
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The plaster crack location is not conducive to mere "expansion/contraction" as the area of wall is way too narrow for that.

More likely is that either it got wet and the plaster dried out rapidly (but there may be water staining to be expected in this case), or some movement of the frame and the reveal. If there was/is foundation movement (of the bay), you could expect cracking or signs in another location. Otherwise probably related to the window renewal mentioned.

Its hard to say, but as the plaster needs to come off anyway, that's the time to look at the wall behind it for any cracking or movement.

As for the heli-bar repair, has that been properly assessed to be the correct repair for the cause? ie will there be further movement potential? It's odd for it to be deemed related to window replacement as there does not appear to be any vertical movement in that photo.
 
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Have the windows now got proper support columns to hold the bay roof up? Helibar in the wall won't compensate for those being missing-it will compensate for no lintel above the opening
Is the bay original or is it an add-on?
Those cracks seem to indicate that the bay has sunk relative to the house. Quite common on older houses (where bays were added after building) to find not much foundation under the bay- might be worth digging a test hole to see how deep the founds are on the bay.
Not a major job to rectify...depending what ground you're on a couple of wind in piles would sort it out. Or rebuild the bay wouldn't cost a fortune


Hi, thanks for replying.

Not sure about the support columns, will removing the blown plaster help reveal that?
The house was built in the 80's, if that helps. The Helibar is being used to target the weak/missing lintel above the bay.
The bay is the original, all the houses on the road have one.

Thanks again for responding
 
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The plaster crack location is not conducive to mere "expansion/contraction" as the area of wall is way too narrow for that.

More likely is that either it got wet and the plaster dried out rapidly (but there may be water staining to be expected in this case), or some movement of the frame and the reveal. If there was/is foundation movement (of the bay), you could expect cracking or signs in another location. Otherwise probably related to the window renewal mentioned.

Its hard to say, but as the plaster needs to come off anyway, that's the time to look at the wall behind it for any cracking or movement.

As for the heli-bar repair, has that been properly assessed to be the correct repair for the cause? ie will there be further movement potential? It's odd for it to be deemed related to window replacement as there does not appear to be any vertical movement in that photo.


Those internal cracks have appeared at different times as at least one of them had a feeble attempt to repair/cover it (you can see if you zoom in) and they've come back. There's some similar (but much shorter and very very fine) hairline cracks in the opposite column. There's also 3 hairline vertical cracks (< 1 mm) in the plaster from the sill to the skirting (one on each side and one in the middle) - my surveyor commented on at least one of these (in the homebuyers report) and put it down to thermal cracking.

And yes, I agree, I want to get that plaster off to see what's going on behind.

The previous owners said they had a structural engineer look at the external crack, and they said a weak lintel and (presumably) recommended the Helibar. It was my surveyor that identified the window replacement as being the culprit of the external crack, based largely on the nature/location of the crack. After I sent him the pics of the stuff that he'd missed (the internal cracks) he said they were a combination of settlement and thermal.

I was wondering if the lateral movement that seems to have caused the external crack could have caused the internal cracking, given the internal cracks location (i.e perpendicular to the lateral movement)

Many thanks for your input.
 
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