Crack in render of extension wall

[Makeitgo]

Hi all

I was wondering if anyone might be able clue me up on a crack I found in the rendering of a wall. We have a circa 1985 extension at the back of a Victorian house and there’s crack in the pebbledash near the corner of this SW facing wall. The crack starts a couple of feet (61cm) from the end of the extension, and zigzags its way down the wall and towards the corner, stopping 1m before the ground (foundation level).

I’ve measured the width of the crack and it’s no more than 2.5mm at the very top, quickly becoming about 1mm wide, then disappears into a hairline at its bottom.

As it’s hard to see the crack due to the rendering being pebbledash, so I thought I’d stick a piece of string parallel to it (at 30mm away to the left), using Blu Tack along the crack’s whole length, as you can see in the photos, as an aid to visibility.

I’ve included a few photos to try and give perspective and I’ve stuck some mini-Post- It Notes on the corner of the wall for scale. The Post- It Notes are at 1ft (35mm intervals) from the top down.

My question is whether this is serious or not. I was wondering if this is caused by aging render, material shrinkage or expansion of whatever flavour or subsidence etc. Obviously I’d rather not suffer the costs of a proper survey unless you guys reckon it’s necessary. Or would the diagnosis be the remit of a decent builder I wonder?

Any thoughts would be very welcome, thanks a lot.

 

[blup]

If it's been there for years probably down to the drying out of the render, it's certainly very random i.e. appears superficial, but you could only test for sure by hacking off some of the render. We've had similar on ours for years and its remained stable and, as you say, virtually invisible

If in doubt a building surveyor or builder would have experience of the issues.

Blup

 

[Makeitgo]

Hi Blup, thanks for your input. I thought I'd put it out there because I'm clueless about this stuff, but I am aware that the direction (route) a crack takes is a big clue as to the route cause of the problem. I've been here years but my attention hasn't been drawn to it until now (new occupant who spotted it). As this one wanders around a fair bit, I doo feel a bit iffy about it.

I guess then, that it might be worth removing some render from the topmost and widest part of the crack to see if there's also a crack in the brickwork underneath? If I did decide to get a surveyor to check it, I wonder if I should hack the render off before they visit or let them see it as it is and maybe then bash some off while they are actually here on site?

 

[^woody^]

Does the crack go down through through the bricks below the render and into the ground? You will have to look close it may be very fine if present

Is it cracked in the same place internally - or if it is plasterboard dry-lined (hollow when then tap the plaster) you may not know.

 

[Makeitgo]

Hi Woody, thanks. As far as I can see without taking the render off, the lowest the crack goes to is about a metre from the ground, so no, it doesn't go all the way to the ground (if that's what you're asking). I would need to take the render off below the point where the crack in the render visibly stops, to be able to check further. The crack is only a hair's width at its bottom though FYI.

I've looked at the wall from the inside and can't see any cracks, however it is wallpapered so I'm not sure what that might be covering up. I'm not even sure if it's a cavity wall, which might also be good to know.

 

[Makeitgo]

Sorry Woody, forgot to say there's no plasterboard involved, it's a solid brick wall.

 

[^woody^]

The crack does seem to go right down to the bottom of the render, but if it does not then foundation movement may not be the most likely.

In that location, going by the tree and the state of the fascia, then it may be more likely a shrinkage issue related to some damp getting to the wall below the render.

 

[Makeitgo]

The crack does seem to go right down to the bottom of the render.

Woody, as far as I can see, the render has no crack in it below 1M from the ground. Are you thinking that in spite of he render's crack only being hairline at 1M, there might also be a continuation of it in the brickwork itself, underneath the render reaching the ground? Eagle eye for clocking the tree and the general environment, this area is in the shade a lot of the time so is not the driest of places and you can also see this by the moss etc. There is also a 6' 8" tall wall 3ft away, running parallel to the cracked wall which causes a venturi of rain past this wall. Also, yes, the facia has obviously seen the elements in the past (not my filling and painting by the way). A few more photos for background...

 

[foxhole]

On south facing wall could be down to shrinkage due to heat.
While it looks very minor it does allow moisture to be trapped behind the render.
Cut out affected area and replace.

 

[Makeitgo]

Thanks foxhole. Looks like you are adding to the consensus that leans towards "it ain't a major issue" (he said with caution). From what I gather cutting out the cracked bit, and I presume you're saying just the crack itself, makes for quite a bit of work to try and make it look reasonably pretty afterwards. I found this post below that basically fills the crack with clear mastic which sounds like an idea. Could be fiddly and time consuming though. Don't know what you think? I also presume that as the render is porous any moisture still in the wall will evaporate. Here's the link:
https://www.diynot.com/diy/threads/repairing-pebbledash-crack.239790/

Cheers

 

[KenGMac]

Makeitgo, good evening.

I recall that 5 year old post??

Such a crack will have allowed moisture to enter, but given the "exposure" on your damaged wall I would consider the volume of water, combined with the lack of driving rain will be low.

The Mastic "trick" in that old post has one massive advantage in that any hack of and re-patch will stick out like a sore thumb forever, when you come to sell an "eagle eyed" conveyancing "Surveyor" will spot the patch repair and start screaming "SUBSIDENCE" we all know how subsidence averse such "professionals" are. Bottom line is that going down the mastic route [if done well] will prevent such issues arising??

Ken

 

[Makeitgo]

Ken, thank you for your contribution and highlighting the main virtue of this technique by helping the "professionals" relax a little : - ). Even without that aspect though, to me it seems a lot less hassle than re-rendering the wall.

My thoughts are also that if this was due to subsidence, the existing crack's width would change at various points after a year (for example). Presumably if it did change, this would be witness to more of an issue than just render. I'm just thinking that by doing the Mastic "trick", it's quite non-destructive and would allow the crack widths to be re-measured after a (arbitrary) year. Smash it up or keep it looking tolerable, I don't know... Cheers

 

[foxhole]

Thanks foxhole. Looks like you are adding to the consensus that leans towards "it ain't a major issue" (he said with caution). From what I gather cutting out the cracked bit, and I presume you're saying just the crack itself, makes for quite a bit of work to try and make it look reasonably pretty afterwards. I found this post below that basically fills the crack with clear mastic which sounds like an idea. Could be fiddly and time consuming though. Don't know what you think? I also presume that as the render is porous any moisture still in the wall will evaporate. Here's the link:
https://www.diynot.com/diy/threads/repairing-pebbledash-crack.239790/

Cheers

Render should have additives which prevent it absorbing moisture and also holds in any moisture getting behind.

 

[Makeitgo]

Render should have additives which prevent it absorbing moisture and also holds in any moisture getting behind.

Thanks for flagging that. So if I did mastic it, it would be best to do it after a long dry spell presumably? So Foxhole, do you reckon I should remove some render from the top where the crack starts and where it's at it's widest. At least if I do that suppose I'll know if there is a crack in the brickwork. When you said "cut out the affected area" earlier, did you mean along the crack line or cut out more than that? Thing is, it's an 11' x 8' wall section and if I removed a few inches of it from anywhere, it would mean re-rendering the whole face to make it look consistent ideally. Forgive me, I'm normally quite decisive.

 

[^woody^]

If the wall is cracked too, then that will need repairing and stabilising, else any new render will just crack again in the same place.

You will never ever get any render repair to blend and match in. Consider just filling the crack with a flexible mastic (polysulphide or polymer) or a cement grout. And then see what happens in the future. This is much less obtrusive.