Crack stitching

[Andy Dingley]

I have a workshop, with a single layer, no cavity, block wall and dubious foundations. It was built some uncertain time ago ('50s? '20s?) by a chap with scant regard for planning or building regulations. The rendering is cracked, and some of these cracks go right through, hence are leaky (no cavity!)

So now I'm looking at possible solutions to stop any movement here, before I start papering over the cracks and trying to get the render waterproof. I'm wondering about a stainless twisted-bar kit like this

- any experience of advice with them?

(Toolstation & Screwfix have similar kits, for nearly twice as much)

My worst cracks are a couple of horizontals and a couple of verticals, both of which appear to be settlement cracks owing to inadequate foundation. It's not so bad I'm having to tie the walls back on, but I would like to stop movement enough to keep the render watertight. Are these helical bars usable in arbitrary chases through the blockwork, or are they only for mortar joints between bricks?

All suggestions welcome!

[John Rumm]

I have seen them used (Helibars I think the trade name was) and they were very effective - they used about three or four of them to tie a 9" solid wall, with a floor to ceiling crack, back onto the back of a large Victorian semi.

They can certainly be applied after the fact. Cut a slot with an angle grinder and bond them in place with the appropriate gloop. The guide on that site you linked seems to include a decent description:

you want to make sure the render can't crack afterwards, hack it off in the area of the repair, and then fix some expanded stainless lath over the area, fixing well with screws and plugs through penny washers on a random-ish 150mm fixing pattern. Then render over.

[Andy Dingley]

Thanks. Any thoughts on numbers or orientation? I'm assuming right angles to the crack and spacing as per their note, but that's for horizontal ties and my two biggies are horizontal cracks.

On the whole, I think I like the idea of using the render as a "canary" in case of further movement. It's not so high that I can't re- render for far less effort than I'd be facing if I did see future movement.

[John Rumm]

If you are rendering over, there is probably no harm in just going perpendicular to the crack regardless of orientation. Obviously with visible brickwork, a bar orientation of horizontal is preferred for any crack since it can be hidden completely in a mortar joint.

So you would need vertical bars for the horizontal cracks, and horizontal bars for the vertical ones ;-) However it strikes me that settlement alone does not usually give horizontal cracks, unless there are also some vertical or diagonal ones near by. In which case you can bar fix the vertical/diagonal ones and then just patch (or resin fill) the horizontal ones.

[meow2222]

You can bond bars in to restore the integrity of the wall, but really its not going to stop the building moving in future. The wall will simply crack somewhere else. Re helibars, ss threaded rod is way cheaper.

A much simpler way to reintegrate the wall would be to inject epoxy into the cracks.

NT

[Andy Dingley]

No, I'm sure it doesn't. But this isn't the "usual" set of foundations!

There are two gable-ended buildings, end-on-end and one narrower than the other. The end of the narrow one is open, spanned by a steel girder about 15' wide. As far as I can see, the root of the problem is that the inner corner is carrying much of the weight of the large gable and also one end of the girder. It gets little support from the wall as there's a door in it, although there is a little buttressing to thicken it, I suspect that the foundations here are inadequate for the load and have settled downwards. The two horizontal cracks (photo) are above this in the large gable and also running from the bottom left corner of the window in the white-painted wall. There's also the vertical crack above this pillar. So the whole pillar seems to have moved downwards by 1/2" - 1" leaving part of the gable above it hanging as an arch(?).

[Andy Dingley]

Helibar are =A35 each, which is cheaper than threaded stainless rod, unless you go down to 8mm. I'd also be concerned about grip on the much smaller thread.

That's going to put the faces of the crack into tension though, so won't that simply peel the epoxy off the crack? The point of the bars is to couple the forces in along a long shear line.

[Tim Lamb]

In message , Andy Dingley writes

I've just bought a metre of m12 stainless studding for a fiver.

Have you totally rejected underpinning?

regards

[meow2222]

I was thinking of smaller than that, M6. The rod isnt going to carry structural weight, it just keeps the wall sections in line so they can bear down on each other.

Why do you think that would be in tension? The concrete is stationary, at least for now. No matter how you bond the bits back, the wall will inevitably crack if/when it moves again, whether it cracks at the same place or elsewhere - and actually its better if it cracks at the same place, a wall cracked into 4 pieces is a lot better than a wall in 8.

Any attempt to stop future cracking just isnt going to happen, unless the root problem is addressed, or the wall replaced with a more flexible type. So unless the place is getting underpinned etc, what's best is a repair that allows a break in the same place in future if it moves again. 20 or 30 notes, an hour or 2 with a ladder and you're done. And with that level of input its no biggie to re-fix it in future.

NT

[Andy Dingley]

Haven't considered it in detail yet. I'm capable of stitching the cracks myself, but probably not capable of doing this underpinning. There are also questions of needing to clear a lot of access to even start looking at it and yet wanting a "quick fix" to water ingress now, even if it's wasted in the future. I can actually see myself doing it with aluminium tape, just to waterproof it temporarily.

There's also a couple of cubic yards of concrete path to replace with grass outside, and some of that's in the corner where we'd be doing the underpinning. At least some of that ought to go before we get started seriously.

Oh, and there's a waterpipe running through the whole mess. Probably in lead. No-one knows quite where. That also suggests there's drainage somewhere nearby, but I can't find that either.

[Roger R]

Settlement or subsidence? Settlement being a one time thing shortly after building. But is there really any such thing as settlement? I have no special knowledge but guess that there only subsidence. Subsidence being an ongoing thing. e.g. the leaning tower at Pisa.

My anecdote refers to the subsidence of an extension to my block built garage. The subsidence was under the far end wall causing the whole extention to tip away from the original structure leaving a tapering vertical crack of up to an inch at roof level on both sides. The crack had occurred at the join of the original and extension. On one side there was a door opening and on the other a window opening with only a few courses of block work, so there was virtually no keying in of the extension blockwork to the original structure.

I tried to repair/solve the problem by replacing the broken blocks and reducing the opening on the side with the window. It did not crack there again, but after six months a new crack from floor to roof appeared a couple of meters further along the garage wall, breaking the concrete blocks in half at that location.

The subsidence could not be restrained by attempting to support the subsiding part by keying it into the existing sound structure, the weight of the extension was just too great for the strength of concrete blocks. Demolition and rebuild of the garage with sounder foundations would appear to be the only effective solution.

My garage is quite different to your building, but the experience would seem to agree with meow222, that the cracks may simply transfere to a weaker point somewhere else. Note that I am not a structural engineer or a builder.

[Andy Dingley]

Settlement, very likely, as the ground conditions aren't conducive to subsidence (major geosurveying works on exactly that, within 50 yards) and the build quality of the whole edifice is best described as "piss poor" with far from adequate foundations.

I've got one of those too 8-) That's on the other side, a different era of building, and I'm planning a 8' tie-rod to deal with it.

In this case there isn't a "weaker point", as I'm talking about a pillar in an internal corner which is the junction of a 15' girder span, a window (white painted in the photo) and a doorway. It's already the _only_ point carrying the load - anything else nearby is an open space. There's a lot of load concentrated in this one spot with not much adjacent to it and that seems to have compressed the inadequate foundations.

Underpinning is a possibility. Jack under the girder, then go underneath it from the existing doorway. Expensive, and it probably involves external contractors.

Simplest is to to assume (nay, to hope) that the existing foundation has compressed as much as it's going to and just deal with the crack. Works fine, as far as your assumption holds.

What I'm most likely to do is to deal with the cracks, then brick up the unused doorway and attempt to transfer some load from the gable away from the pillar and into this new ex-doorway masonry, on an adequate foundation.

[Tim Lamb]

I'm no expert but... a chap who does odd bits of groundwork for me specialises in underpinning work for the insurance companies. We were discussing how to go about creating concrete pads to support a steel portal frame inside my timber barn. The architects have drawn a fancy Acrow propping arrangement to take the load off the foundations. He said this is unnecessary as most of his work is done by simply undermining the foundations in 1m blocks and back filling with poured concrete. Apparently the jobs sometimes require rammed dry mix for the 2" or so actually in contact with the original foundation. Cue Huge:-)

Better the deed, better the day!

Just think how much more easily you will rest not supping leaded water.

regards

[george (dicegeorge)]

there is some way of cementing in a scale which you can measure in a year to see how much movement there is... let me know when you find it out cos ive got a few cracks too... (in my house that is)

[g]

[Andy Dingley]

Had a couple of those in my first house - a terrace on a steep hill. You could see one of them move out 1/4", then move back later in the year.

[Andy Dingley]

One of our neighbours used the same technique on his barn -- Or "the rubble pile" as it's now known, Plain poured concrete has a ****ing terrible reputation for underpinning, as it's difficult to get adequate compaction with it and then you get the same old settlement problem.

If I did underpin this, then I'd have to prop the girder. If I prop the girder, the rest is easy (working the hole from outside). Still a big job, and a Summer job though.

[John Rumm]

A mate of min used to do similar stuff - often with angered piles to pin the resulting concrete beams in place. Apparently they would use the same undermining hit and miss technique, then they would insert disposable jacks to prop up the bits they had undermined. Then undermine the rest. Make up some rebar cage forms ready for the concrete pour (if piles were involved then these would be done first and their tops and rebar would be integrated into the beams). Then pour the concrete. Once that had gone off, slate or dry pack could be used to take up any shrinkage (plus the jacks would still be in place obviously).

[John Rumm]

Quite often done with three measuring points either side and above the crack (most are slightly diagonal). These are epoxied into drilled wholes. Just take readings between them with callipers.

[Andy Dingley]

What do you think the timber framing training workshop is for! 8-)

[Andy Dingley]

He needs one of those air suspension seats when he's driving the digger...