Repairing structural cracks

[Nigel Watts]

The subsidence affecting my small two storey rear extension went into reverse and has now settled down following the removal of a very large Eucalyptus tree from my garden last year.

I have had an engineer's report telling me what I should do to make good. She recommended that the larger crack on the upper floor should be reinforced by the insertion of "helibars" resin bonded in place as recommended by the manufacturer.

If suspect that this is rather too far towards the "hairy arsed" end of the spectrum for me, espeically now that I am into making dresses and curtains, but I am nevertheless interested to know if anyone has done this kind of thing themselves or hired someone to do it for them. Cutting the slots in the brickwork to take the bars would the the painful/dangerous bit I guess.

 

[Flyfisher]

We had some walls stabilised using helibars. I didn't do the work myself but I paid close attention and it didn't seem too difficult as long as you can safely handle an angle grinder and/or long masonary drills.

Presumably your engineer would specify the placement of the helibars? Position, depth, that sort of thing.

Glad to hear that the movement problem has been stabilised though.

 

[Penners]

Nigel - as FF says, I really don't think the job should be too challenging. A bit hairy-arsed, perhaps, but mostly dusty-arsed, from all the masonry cutting. And that will be the case whether you do it yourself, or get in a professional.

You can hire all kinds of masonry cutters from your local hire centre. You just need to discuss with them the best tool for your particular job. I suspect that the most critical factors will be the depth and type of cut that you want to achieve.

Here's one type of masonry saw - you can get them electrically- or petrol-powered:

 

[Nigel Watts]

I am already feeling terrified!

 

[Flyfisher]

No problem Nigel, just start it up like a chainsaw, hop up a ladder and start lashing out with it! :wink:

More seriously though, the tool in Penners' photo can be a bit fearsome. I've only used them for cutting paving slabs, where you can stand over the work and properly brace yourself while holding them. I wouldn't fancy trying to cut deep channels in vertical walls with one, but I've seen it done and, like most things, an expert user can make it look easy.

Personally I tend to limit myself to an electric angle-grinder with a diamond cutting disc, which is far easier to handle (lighter and smaller) but is also, of course, more limited in the depth of cut.

 

[AMc]

Not sure what you need to cut into the wall? - if it's just light chasing then my electrician used a dedicated tool with an attached hoover - it made so little dust you could stand next to it with no mask. I would hire one of those.

My experience of those 9" and 4" angle grinders on masonry is they generate so much dust its hard to see what you're doing after 10 seconds - I would avoid using one in a decorated room unless there was no alternative. Likewise I wouldn't use a grinder on anything less than a scaffold tower or real floor - ladders a no no for me!

The chemifix (sp?) resin is fairly easy but hideously expensive about £25 a tube - we used it to fix the wall plates on our vinery and it is amazing stuff.

 

[Feltwell]

A Stihl Saw (the beast in Penners photo!) is a bit much for helibars. What is the mortar? If lime you could do it with a plugging chisel. If cement a 4 1/2" grinder with a diamond disc is easy enough to control, with care (and making sure that direction of rotation is blowing all the dust away from you) I'd happily use one up a ladder, especially if you have a stand-off bracket for the ladder.

 

[MdB]

My wall chaser (£40) will do 40mm depth and creates a fraction of the dust of an angle grinder when connected to a vacuum. Mine still requires a mask but I would never chase a wall with anything else as it does such a good job. It is heavy though and I don't think I would want to use it horizontally just due to its weight. It is also fairly difficult to get a cut in exactly the place you want as the discs are covered.

As Feltwell says, I would happily use a 4 1/2" grinder up a ladder though this might not cut deep enough for what you need. Make sure you use a diamond cutting blade rather than a non diamond stone cutting blade. The diamond type are easily worth their extra cost.

I would think twice before using a 9" grinder up a ladder (smaller than Penners' monster). I probably would but it is something I would be careful of. They kick quite a lot when they start up (at least my cheap one does).

Oh and the cheapest place I found helifix bars was at Mike Wye (of all places) though they may not have the right size you require.

 

[Penners]

The critical thing - as has been observed above - is the depth that you need to cut. If you don;t need much depth, then of course a chaser or an angle grinder are best. But if you need to get really deep, then you need a larger diameter wheel.

 

[Andrew Bodenham]

Nigel,

I wonder a bit about your engineer's advice. Of course I've not seen the situation, so I'm mostly guessing. If there has been relative movement between the old and new parts of the building in the past then there is a fair chance that there will also be some movement in the future, albeit of smaller magnitude now that the primary cause has been removed. Given the very large forces involved I can't see how the addition of a few bonded metal bars would prevent future cracking. If anything they would tend to cause stress concentrations in the immediately surrounding brickwork, possibly leading to cracking in places other than the interface between old and new. Unless the aim was to provide some lateral stabilisation I'd be more inclined to think about creating a flexible joint between the old and new work, using something like polysulphide mastic, or a compressed PU foam strip. This would allow for movement whilst maintaining weatherproofing.

 

[Nigel Watts]

Andrew I rather agree with you. I may give the bars a miss.

 

[philpjuk100]

Hi we had a heli bar repair done on some cracks in a 70s bungalow,the bars were installed deep in the brickwork with some "hi tech" resin,the mortar was cut out,dust blown out,the slot primed,the bars glued in and finally the mortar made good (oh how I wished he had matched the new mortar with the old!) The chap who installed them showed me some that allowed movement,one half was glued in and the other half ran in a tube that was glued in!(did not really understand why? but english was not his first language!) Three years on there is no new cracking.The reasons given by the engineer were that the heavy ivy growth on the house had removed the moisture from underneath and removal of the ivy had allowed movement which had now stabilised,hope he was correct!

 

[Feltwell]

The chap who installed them showed me some that allowed movement,one half was glued in and the other half ran in a tube that was glued in!(did not really understand why? but english was not his first language!)

There are occasions where you want to restrict movement in one plane, but allow it another - usually for expansion/contraction purposes. I've seen it done in long retaining walls, and where 2 structures join - e.g. a retaining wall butting up to a bridge abutment. If the wall is falling forward you want to restrict it's movement by tieing it to the bridge abutment, but you still need to allow it to expand and contract along it's length or it will quickly crack.

Uses in a domestic setting would be fairly limited.

 

[philpjuk100]

Yes,that makes sense,I suppose some flexible mortar/mastic would be used,I have noticed breaks in brickwork in large walls in a new local shopping center,must be there to avoid stress.