advice on interesting settling/bodge job :)

[mylovelymonster]

Dear all, but maybe particularly PigletJohn - we have removed a cupboard which was in the corner where single storey extension meets main house and found an interesting slightly diagonal/crazed crack, starting approx a quarter of the way up the wall to the top corner. Maybe a couple of mm. No sign of movement at ceiling level. It is in the plaster on the original external wall rather than the 90degree abutting (new) wall. material either side of crack may differ - dark grey versus pink plaster. The new wall is a double skin wall and the other side is a conservatory which shows no obvious signs of movement. At first we thought - is the new wall moving away, but other side looks fine. We've taken up the carpet in the problem corner and lo & behold it looks like the builders bodged the floor around that new wall - floor screed is broken up/powdery and what looks like foam beneath the new wall!! - for a couple of feet, so thinking the crack could be due to slight movement downwards. Not sure how far underneath the wall is a problem.
So, how to sort? Is single storey. Do we need to and can we improve rigidity under that part of the internal wall? The building works are 6-7 years old. Could we fix with a simple influx of liquid concrete screed in that corner? Time to call a structural engineer?

Re: survey - we had a full structural, and the crack would have been clearly visible inside the cupboard, if he looked, which might have flagged up potential problem. Is it worth returning to the chartered building surveyor who did the survey (December last year).

TIA for any input. Please don't be scary. I am feeling a bit delicate

Hi.
I don't really understand your description of the wall arrangements, but if you have different plaster either side of the crack then it is quite common to get movement on the joint. Possibly shrinkage of the new pink plaster. No point getting an engineer or surveyor in just yet. The most basic form of monitoring is to put pencil lines either side of the crack and just keep measuring between the same points every month for a year. Keep a notebook or a spreadsheet of the measurements. If there is structural movement your measurements will pick it up and your records would be used as part of an insurance claim. Seeing as you have taken down the cupboard, the next best thing is to fill in the crack with polyfiller, decorate and sit back. If it reappears then add the pencil marks and measure above. TBH if you don't have similar cracks on the other side of the wall, then you probably don't have structural movement, but only time will confirm this. If it doesn't come back, or it only comes back lightly where the plaster joint is, but doesn't get wider (or open and close with the seasons) then happy days!
HTH

Thanks Tricot. We were going to chase out and repair until we saw what was happening at floor level. Do you think we have a significant flaw in construction which needs looking at? We're about to prep the space for decoration and new flooring, and don't want to go down that route if the wall might need underpinning. Should it not be solid underneath entirity of wall?

If i understand rightly you are worried about the base of a new wall which runs off the old/cracked wall at 90°?

Run your palm across the crack and see what "out of plane" movement you can feel. If the new wall is causing the crack it will be pulling part of the old wall and so the crack will feel like there is a step. Iyswim?

Screed often fails so that is not necessarily anything to worry about on its own. You could maybe lift the broken bits and see if that lets you see more "foam". Could the foam possibly be just a gap filler or bodged in to fix the skirting? Maybe do a small bit of digging around.

If you only have one crack between materials and some cracked screed without other signs of movement in other walls/distorted doors etc it doesnt sound like a massive problem from what you have said. Any other signs or symptoms?

Good morning
Ok - the cracked bit on the old wall is cracked/fractured a few inches from the corner with the new wall and there is a crack aligned with the corner also - so a thin section, which is lifted away 1mm or so. Where it is not cracked on the old wall, lower down, it is cracked in the corner by 1-2mm. It seems that it is this corner that is the problem - with the narrow section extending between the two walls, raised about 1mm max. The ceiling seems fine - just fine cracks where the walls and ceiling meet, slight feathering.
I guess we will know more when we chase out the duff area and see if there are cracks in the blockwork. Is interesting getting down the the nitty gritty of a building!
We have lifted up more of the carpeting and found the same foam strip at the external threshold, so are thinking this is some sort of insulation between the floor and external walls/space, so I think legit - just depends on whether it's been done as it should have been.
Have to add that we have found that one part of the guttering from the roof just ends at the ground - no channel to take water run-off, so not sure everything was done as it ought to have been. The timber cladding is quite poor also! Who knows what might be discovered when that comes off. The window opposite the offending corner is very stiff on one side - DH reckons it was put in very badly and hasn't been used/full of building dust. Otherwise, no signs of bowing or cracks around it apart from hairline beneath sill to floor, behind radiator.
Other rooms in the extension (beam&block base) all have fine cracks linked to windows - single, from underside of sill to floor - which I would think was fairly normal!
I am feeling calm about it now - just if there is possibly an issue, I would like to address it now rather than a few years down the line after we've decorated and become too attached!

Really really appreciate your input
Do you think it would be useful to have some structural investigation? Or wait to see if the blockwork behind the plaster is damaged first?

.....it could be that the plastering job at the interface was a bit bodged and the materials have just shrunk differently.................that would be best case
Fingers crossed....

It is not bodged necessarily. Plaster cracks at the junction of different materials so between brick and block walls, or masonry & plaster are sort of normal.

if you had a single-storey extension, it may be that the foundation of the extension was shallower than the rest of the house; it will certainly have been separate, and is likely to move independently.

If the plaster over the crack is hollow-sounding when you knock it with your knuckles, hack it off and see how much of a crack is in the wall. If it is narrower than a matchstick and only in the mortar, it is not much of a prob. If you can push a pencil through the crack, or the bricks are cracked, I would be more concerned.

If the crack has been there five years or more, and is not getting worse, it is not very worrying.

Is your house on deep clay, for example in London or Bedfodrshire?

I am finding it difficult to concentrate after a late Sunday dinner with extras, sorry.

a modern concrete floor will often be laid on an insulating foam slab, with foam strips round the edges between the floor and the wall to prevent heat loss from floor slab to external wall. Could that be the foam you mentoin?

Hullo - clay over chalk, yes. The rest of the extension looks tidy - a crack in the floor across a threshold to another room we've uncovered, but nothing to raise too much concern, I don't think. Just the problem corner looks quite spectacular - very jagged/feathered, and cracks extending from top to bottom in different places - but gap not that big. We'll see what's behind the plaster!

Am hopeful we can put it down to the new building settling over the (6?) years since built, and this corner being a bit more interesting due to old meeting new.
The foam seems just as you've described - made sense when we lifted the carpet last night and found it elsewhere around perimeter. Hopefully it doesn't extend too far under the wall and that the blockwork is properly supported! I trust that it has been done reasonably well - the builders that did it have quite a good rep here. If we find issues behind the plaster, I'm sure i can get them over & give them an earful.
Thanks for your knowledgeable input - is reassuring. There is a lot to do here, and we have found a number of (annoying) things we didn't expect to need doing, so sensitivities are running higher than usual.
If you're a bit stuffed after dinner, a gentle walk is a good idea. Do you have a dog?