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trevor saxe-coburg-gotha |
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trevor saxe-coburg-gotha World Chat Champion
Joined: 22 Nov 2012 Karma :
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Posted: 05:36 - 22 May 2017 Post subject: potential red ash problem - property near Howden |
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Mate just rang me to say his kitchen floor has erupted! Afaict, the the property was changed from wooden boards over joists type of construction to a more modern concrete base style some time during the early '70s.
This reminded me of an issue in Stoke where I used to live, where there was a problem some years ago. Potential buyers were getting refused mortgages for this thing called "red ash". It was quite a problem locally.
So while he was telling me about his floor I quickly googled "red ash" - and what he was describing seemed to be what happens when this kind of cheaper material is used as a base for concrete overfill. Basically, something in the ash reacts with part of the concrete which, combined with moisture and - apparently - movement caused by mining subsidence, not only weakens the floor but also brings about a quite violent (albeit insidious) structural failure in the floor.
But my question is could this be happening as far afield as Howden? From my admittedly cursory googling, search results seemed to relate only to Stoke on Trent. Seems unlikely the problem would be confined entirely to there, but I was wondering if any of you guys with knowledge and/or experience of the building trade had encountered the problem further afield. And also what kind of work is required to treat the issue.
On this latter, I seem to remember the simple answer to that is "extensive". I.e. excavating the flooring and foundations through the entire property minus the bits the walls stand on, and replacing with proper lime hardcore and then concreting onto that.
The cost, inconvenience and hassle seems almost insurmountable and I'm scared my mate's facing very serious problems with his house. ____________________ "Life is a sexually transmitted disease and the mortality rate is one hundred percent."
Mobylette Type 50 ---> Raleigh Grifter ---> Neval Minsk 125 |
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doggone |
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doggone World Chat Champion
Joined: 20 May 2004 Karma :
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Moo. |
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Moo. World Chat Champion
Joined: 11 Jan 2009 Karma :
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Posted: 07:53 - 22 May 2017 Post subject: |
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Sounds like it could be a sulphate attack on the concrete floor. Have a read of this blog post, Joe Mallone is a top notch inspector that deals with the wierd and wonderful.
There's two blog posts on that page that refer to a sulphate attack case and how they remedied it.
https://buildingdefectanalysis.co.uk/category/flooring-defects/
EDIT: Did a Google search on Red Ash Sulphate and it seems it probably is related, red ash is the hardcore infill used below the concrete slab. Just a snippet stolen from the above posted blog...
"Sulphate attack is caused when sulphates contained within the concrete aggregate contain sulphates or the hardcore sub-base below the concrete contains sulphates. These sulphates react with the Tricalcium Aluminate in ordinary portland cement (OPC) to form Ettringite, a crystal that expands as it grows, in the process often causing substantial damage to the concrete floor slab. Moreover there can be consequential structural damage as heave within the floor can displace internal walls built off the floor or indeed displace brickwork in the outer perimeter walls." ____________________ A2 Passed 18/6/10
Last edited by Moo. on 07:58 - 22 May 2017; edited 1 time in total |
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BTTD |
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BTTD World Chat Champion
Joined: 22 Nov 2012 Karma :
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Pete. |
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Pete. Super Spammer
Joined: 22 Aug 2006 Karma :
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Posted: 09:00 - 22 May 2017 Post subject: |
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Moo. wrote: | Sounds like it could be a sulphate attack on the concrete floor. Have a read of this blog post, Joe Mallone is a top notch inspector that deals with the wierd and wonderful.
There's two blog posts on that page that refer to a sulphate attack case and how they remedied it.
https://buildingdefectanalysis.co.uk/category/flooring-defects/
EDIT: Did a Google search on Red Ash Sulphate and it seems it probably is related, red ash is the hardcore infill used below the concrete slab. Just a snippet stolen from the above posted blog...
"Sulphate attack is caused when sulphates contained within the concrete aggregate contain sulphates or the hardcore sub-base below the concrete contains sulphates. These sulphates react with the Tricalcium Aluminate in ordinary portland cement (OPC) to form Ettringite, a crystal that expands as it grows, in the process often causing substantial damage to the concrete floor slab. Moreover there can be consequential structural damage as heave within the floor can displace internal walls built off the floor or indeed displace brickwork in the outer perimeter walls." |
I think his only saving grace is that the floor was a replacement for timber so none of the walls will be built off it. If it's already heaving though they better do something quick to relieve any outward-bearing pressure since the slab will expand in all directions but when it gets jammed on the sides the only way is up. Chase around the wall line or something to relieve outward pressure.
Since the floor is already heaving then breaking it out should not be too big an issue. I would fetch a breaker and do one room at a time. Break out the slab, lay a barrier over the substrate and put in a new slab with foam expansion around the periphery. Hell since it's a non-load-bearing slab just wack the substrate flat, throw down 2" of jablite and screed over the top. The jablite will form the barrier for the sulphates. ____________________ a.k.a 'Geri'
132.9mph off and walked away. Gear is good, gear is good, gear is very very good |
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chrisdubya |
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chrisdubya Scooby Slapper
Joined: 05 Jun 2015 Karma :
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Posted: 14:52 - 22 May 2017 Post subject: |
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Pete. wrote: | Moo. wrote: | Sounds like it could be a sulphate attack on the concrete floor. Have a read of this blog post, Joe Mallone is a top notch inspector that deals with the wierd and wonderful.
There's two blog posts on that page that refer to a sulphate attack case and how they remedied it.
https://buildingdefectanalysis.co.uk/category/flooring-defects/
EDIT: Did a Google search on Red Ash Sulphate and it seems it probably is related, red ash is the hardcore infill used below the concrete slab. Just a snippet stolen from the above posted blog...
"Sulphate attack is caused when sulphates contained within the concrete aggregate contain sulphates or the hardcore sub-base below the concrete contains sulphates. These sulphates react with the Tricalcium Aluminate in ordinary portland cement (OPC) to form Ettringite, a crystal that expands as it grows, in the process often causing substantial damage to the concrete floor slab. Moreover there can be consequential structural damage as heave within the floor can displace internal walls built off the floor or indeed displace brickwork in the outer perimeter walls." |
I think his only saving grace is that the floor was a replacement for timber so none of the walls will be built off it. If it's already heaving though they better do something quick to relieve any outward-bearing pressure since the slab will expand in all directions but when it gets jammed on the sides the only way is up. Chase around the wall line or something to relieve outward pressure.
Since the floor is already heaving then breaking it out should not be too big an issue. I would fetch a breaker and do one room at a time. Break out the slab, lay a barrier over the substrate and put in a new slab with foam expansion around the periphery. Hell since it's a non-load-bearing slab just wack the substrate flat, throw down 2" of jablite and screed over the top. The jablite will form the barrier for the sulphates. |
+1 on sulphate attack however, there have been instances where the floor expands as you say, but once it reaches the external walls (in properties with a physical DPC in the walls) it can actually push the walls out as the DPC acts as a slip plane. |
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mas101 |
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mas101 Borekit Bruiser
Joined: 26 Sep 2016 Karma :
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Old Thread Alert!
The last post was made 6 years, 331 days ago. Instead of replying here, would creating a new thread be more useful? |
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