potential red ash problem - property near Howden

[trevor saxe-coburg-gotha]

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.
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[doggone]

If he does have to do the floors good chance to put insuation under and consider underfloor heating at least some rooms.

[Moo.]

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."
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[BTTD]

It won't be cheap, but then I would hope that the house insurance will cover it.

Failing that, your friend should buy a cement mixer and shovel. He has a new hobby called mixing concrete.

[Pete.]

[chrisdubya]

[mas101]