Cracked /Blown plaster.

[lukus]

Hi all,

I've started redecorating a room; putting wood flooring /skirting in and repainting. One of the walls (side of house) the plaster was heavily blown. Crack wise it wasn't too bad considering almost the whole wall had blown away from the brickwork...

Now that it's back to the brick work I can see several cracks - all relativly hair-line-like but some considerably long spanning several bricks and exploiting the cement every other row (i.e. the cracks are striaght vertical lines, not stepped). Also some of the cementing looks a bit crap i.e. some gaps where it has fallen out and partial attachment, mostly in the central area of where it blown...

Now this wall is an outside wall (part of the extention that was added no later than 20 years ago). The room next to this one (room 2), on the same outside wall had a couple of rather big cracks in the plaster and maybe it was lightly blown around that crack but nothing compared to this, and it's also spaced away i.e. doesnt seem to be related However, directly downstairs room 2 there was a big crack that was professionally looked at /fixed - nothing was done to the upstairs room even though it was visibly cracked in plain sight...

I can't remember what the problem downstairs was, since it's my mothers house - I'm just doing this room up while she's on holiday... I don't think there was anything "wrong" with this outside wall when it got checked out and the crack was just filled in. Will I be safe ignoring the cracks in the brickwork and plastering this wall?

Doesn't really look too bad, I just don't expect a crack to slice through 1-5 or so bricks in a line.

can post a pick later when it's daylight if needed

Cheers,
luke.

 

[Richard C]

Will I be safe ignoring the cracks in the brickwork and plastering this wall?
Doesn't really look too bad, I just don't expect a crack to slice through 1-5 or so bricks in a line.

Hairline cracks that are just in the plaster can usually be successfully repaired by using a strip or two of fibre glass reinforcing tape & then re-skimming. Cracks that look more significant really need to be further investigated & I always dig the whole area away around 150-200mm either side of the crack to expose the block work beneath; I assume its blocks? If the pointing or the blocks them selves are cracked then more substantial repair & reinforcement with metal lath is required before replastering or the crack will almost certainly reappear. I repair any pointing around the blocks & fit the lath, again around 150mm either side of the crack, apply a render base coat over the lath & build out to the surrounding wall with a skim of Bonding plaster; I then re-skim the whole wall. This is time consuming but a mostly successful method of repairing a wall to its original state but there can be no guarantees the crack won’t reappear if the wall is still moving around. All this assumes there are no corresponding cracks on the outside which may indicate more substantial movement & metal lath support will not hold that together.

Another method worth considering if the whole wall has been stripped back is to dot & dab some 12.5mm plasterboard over the whole wall, tape & skim. A bit like “papering over the cracks” but it’s less time consuming & usually successful if the wall isn’t still moving around; if it is you’ll most likely get cracks along the board joints but in extreme cases the boards them selves can crack!

Success or failure really depends how bad it is & providing there is not still excessive differential movement in the wall. Some pics may be usefull but it can be very difficult without seeing it in the flesh & having a good tap around the cracks.

 

[trowelmonkey1]

pics would be a good start chap.

doesn't sound like your average crack if it's dividing bricks in half

what does the wall look like outside?

if you re-plaster you could well end up with cracks in it if this is an ongoing problem, so it's worth putting some thought in to this one, you don't want to come back and re-do any of this even if it is your mom's place.

it sounds like the least it needs is the mortar raking out and re-pointing though.

 

[Richard C]

doesn't sound like your average crack if it's dividing bricks in half

Tis surprisingly common with large block work walls but doesn’t necessarily mean serious problems; this sort of repair (mostly successfully) is one of my specialties & some I've done have looked terrible initially.

 

[lukus]

Hiya thanks for the replies.

here are some pics, they are all vertical cracks though.

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• lukus
• 13 May 2009
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• lukus
• 13 May 2009
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• lukus
• 13 May 2009
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• lukus
• 13 May 2009
• 1

Pic 1 is the longest crack on the wall
pic 2 close up of crack 1
pic 3 another crack...
pic 4 patchy bonding, only this small area.

cracks on pic 1/3 are the worst on the wall, all the others are a lot less 'thick'

Out side wall is rendered on the top half lol (if thats the correct term). Has a few long cracks but thats looks normal to me, they were also filled in by who ever painted it last time and they've not reopen since (and this is a couples years ago it was done at the least.

 

[trowelmonkey1]

oh blockwork as opposed to brickwork! less scary then.

i'd still want to know why this has happened, maybe richardc can give us some clues as to its cause? please.

repairing should be no more than re-ponting the bad area of mortar then plastering unless there is something in the cause that needs addressing?

 

[roy c]

This to me looks like bad footings, if the wall has cracked like that (inside and out) then it has moved. It may be weak mix of concrete in the footings or the footings were not deep enough when extension was built. Also looks like a "suspect" mix on the block-work.. May be worth getting a structral engineer to have a look at it. Have you got a "Habitation Certificate" that would have been issued by the building inspector when the extention was finished? Thats if it went thru the right building application's.....I may be a bit over the top with my opinion but better to be safe eh?

 

[lukus]

Thanks for the replies again guys,

Roy C, funnily enough my dad was talking about when he had that extention done a couple of weeks ago and the foundations /footings etc.. were done a bit deeper /bigger because of a pipe going through from next door which shouldn't of been there so it should be better than the house the extention is attached to. lol

Out side the brick work is fine the top is rendered over but the bottom half is visibly clear. Rendering has 3 cracks but looks fine and certainly unrelated.

It was also properly built dont worry, it was my dad that had it done and he's a painter so he would of had it done properly

The wall was inspected previously or should have been when there was a big crack downstairs so I'm sure we have some recent certification about 3 years ago saying it is structurally sound... I think downstairs was also just a cosmetic repair come the end of it...

Also the plaster has been 'blown' for a few years, without really cracking or changing. I'm thinking the wall is probabily fine and the plaster probabily came off in the first place from the abuse given to that room

 

[roy c]

You dont get cracking in brick or blockwork,(horizontal or vertical) if everything is sound and the reason the render came off was probably associated with the cracks and movement.....Dont matter how deep or wide the footings are if the concrete mix is not right!!!! Hope I'm wrong.......

 

[Richard C]

You don’t say when the property was built; during the 60’s & 70’s building booms, there were even more dodgy builders around than there are now! Building Regs. as we know them had only just been introduced & I suspect enforcement was far more lax than it is now; with some of the pointless, PITA regulations we now have to comply with I sometimes wonder if that may have been a good thing! Dodgy materials & mixes + the depth of many footings would be considered marginal by today’s standards so older properties tend to move around more but it doesn’t mean they are going to fall down. Cracking in the external render is one thing but if you have any corresponding cracks in the external brickwork then it would be wise to investigate further & get a professional opinion; I would consider this more significant than cracks on just the internal blocks which are very brittle.

Apart from the odd extension, practically all of the work I do is renovations of one sort or another. As I said earlier, a lot of this work involves repairs to cracked internal block work very similar to those in your picture which are usually (but not always) vertical. I find they are very common & yours look minor in comparison to some I find. I’m confident either of the solutions I’ve suggested above will work & in most cases will provide permanent repair but you need the steel lath reinforcing to bind it together or it will definitely crack again; at the end of the day, it’s your call!