Screed floor crack - now fixed!

OK - been a while... But I have now completed work to fix a crack in my new floor screed.
Recap: Screed is microfibre loaded 3" thick, sits on 3" celotex, which sits on 4" concere on Type 1 MOT.
The builder used 3 50mm scaffold poles to act as rules, one in the centre and one at each side. Poles were removed and filled in. This *I believe* is the cause of the fault - along crack right along the path of the centre pole zone. The crack switches from side to side of the 50mm trough so I think it's due to the infil screen not integrating its microfibres properly with the first laid screed.
Basically a 50mm deep weak point the full length and two more zones that may be weakened.
Picture of the crack:
http://www.flickr.com/photos/timjwatts/11584826156/in/set-72157639079335043
John Rumm suggested helifix, so after a bit of research that led to the discovery that:
1) Screed crackes are well known in industry;
2) There are some stock repair solutions.
The solution I chose was this stuff:
http://uzin.com/products/product-search/details/uzin-kr-416-219/
A 2 part low viscosity acrylic resin used together with M3 Stainless threaded bar as ties.
This means cutting 4mm wide 30cm long 25mm deep slots perpendicular to the crack and crossing the weak zone and well into the good areas both sides (hence 30cm long slots - normal crack repairs are done with 80mm slots).
Another piccie of slots:
http://www.flickr.com/photos/timjwatts/12156279233/in/set-72157639079335043 http://www.flickr.com/photos/timjwatts/12156947806/in/set-72157639079335043
There was evidence that the crack goes deeper than 25mm so was not superficial.
The 4mm wide cut was done with a cheap wall chaser I already had with both diamond blades mounted together. Slightly dodgy but there seemed to be no ill effects and I was well protected by the metal cowl plus googles.
I did make sure to align the dust clearance slots in the 2 discs though - pretty sure it would not have liked it otherwise.
3:1 screed is very easy to cut and with a hoover on the back of the wallchaser, very little dist was produced though I did sheet the conservatory first to avoid excessive cleanup effort.
After hoovering the floor and slots, todays job was to take the M3 SS threaded bar I got from Metals4u.co.uk and chop it into 30cm lenghts with my small bolt cutters. After that, a couple of rinses in petrol to remove machine oil and left to dry.
I used some old food tins, well cleaned to mix the KR416 resin half a pack at a time (3 packs, so 6 batches). I used 1/4 of the supplied hardner powder per 1/2 batch which should give me a pot life of 20 mins (it did near enough).
Many many dire warnings about the resin's toxicity - it was very stinky and the powder was annoying as even careful dispensing always had some wafting about - weird smell, mixture of "chemical" and "sweet". The liquid resin just stunk of a solventy type smell. Lot of ventilation obviously and rubber gloves on.
I used some cheap 1/2 litre empty bottles with nozzels ("glue bottles") from ebay and some cheap throw away funnels to load each resin batch into a bottle with a fine nozzel to make filling the slots easier.
After that, it was a piece of cake. Fill slot with resin - chuck 2 threaded bars in (double strength as M3 was the biggest a 4mm slot would take). Repeat. Come back and top up slots as the resin is *very* seeking and soaked into the screed and along any cracks. Managed to inject some into the top of the crack too which was readily taken up.
As per instructions, I dusted with fine pure sand. Some sank into the resin - acting as filler - that's OK. Came back and dusted more later so the top of the resin was fully blinded with sand.
Pictures:
http://www.flickr.com/photos/timjwatts/12156651383/in/set-72157639079335043 http://www.flickr.com/photos/timjwatts/12156706863/in/set-72157639079335043 http://www.flickr.com/photos/timjwatts/12156718133/in/set-72157639079335043 http://www.flickr.com/photos/timjwatts/12156665013/in/set-72157639079335043
Anyway - thanks to everyone for suggestions - as usual some advice was used as is, some lead to directed reseach that lead to this.
Not hugely expensive to fix. More than TNP's PVA idea (that worked for him). However, I felt this one warrented steel ties and having decided that, the Uzin resin is definately the right product for the job mostly as it is very low viscosity so soaks in and should distribute the tie load though the screed better than say car body filler that would only surface bond.
Enjoy the pics :)
Now I can order the bloody tiles!
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Tim Watts wrote:

I would, if all apart from the first one weren't 404
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On Sunday 26 January 2014 18:59 Andy Burns wrote in uk.d-i-y:

I set Permission: Public -
Hold on - bloody Flickr...
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On Sunday 26 January 2014 19:13 Tim Watts wrote in uk.d-i-y:

How's that?
It may have been that I changed permissions but did not finished by clicking Flickr's "Thanks" button...
They load for me in Chrome Icognito...
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Tim Watts wrote:

yes, fixed.
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On 26/01/2014 18:53, Tim Watts wrote:

That is very rich mix for screed .. may be reason for crack ... unless you have found the cause.
Richest I have ever used was 4:1
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Nice job - I did something similar to reinforce a cracked breezeblock wall years ago, but just with mild steel threaded rod and injection resin. I'll remember that Uzin stuff, seems very handy. The soak-in aspect especially.
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On Wednesday 29 January 2014 21:47 Steve Walker wrote in uk.d-i-y:

Thanks!
The smell has almost subsided! (I think it is the solvent). Got a heater in there to drive the last bits of stinkiness off.
These folk seem to be the only suppliers I could find outside of German ebay:
http://www.pwflooring.co.uk/subfloor-preparation/preparation-and-repairs/uzin-kr-416.html
Used these to "inject" it:
http://www.ebay.co.uk/itm/eep/130644009737
and a handlful of cheap funnels from ebay to decant.
As I was afraid of the pot life, I used a couple of old full size food cans (washed) to decant 1/2 a tub at a time into. Hardener was metered out with a cooking tablespoon measure (thrown away of course!).
Turns out if you have everything ready, it goes down pretty fast - I could probably have mixed whole tubs at a time as I was using half- measures of hardener for a longer 20 min pot life.
I did rung Uzin and check it would not eat my polybutylene UFH pipes - they said it was fine for those and PEX pipe too. Apparantly it eats expanded polystyrene - but I'd used foil faced celotex under my screed so luckily that was not a problem.
Cheers
Tim
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