concrete floor sagging in middle


I have a concrete kitchen floor which is sagging in the middle, it has hardboard which is pretty thin now over the top. It is rented accommodation and my landlord has arranged for a joiner to lift the board and a plasterer to screed the floor. It is an upper floor flat and I am concerned that without finding out why the floor is sagging that the extra weight might collapse the floor into the downstairs property. Any advice?
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"Mandie @k@ Zepherous" wrote:

Was this floor sagging when you moved in or was it level and then sagged? Concrete isn't flexible - if it has changed shape it will have cracks in it. Has it got any cracks in it? Are there any signs of structural failure in the ceiling immediately below your kitchen in the downstairs property? Is it possible that the concrete wasn't level when the floor was laid and it has had a dip in it since then? Anything beyond this diy approach will need the services of a building surveyor or structural engineer.
http://www.localsurveyorsdirect.co.uk/
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after I got a new kitchen fitted, I don't know if that has any relavence though ?
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Concrete will only sag if it's trying to hold more weight than it can handle - including its own. And if it sags, it cracks and so loses all its strength. I most certainly would not want to stand on sagging concrete until I discovered how strong the supporting material - i.e.joists in this case - was. If the joist are rotten the whole thing could fall in at any time, even without the weight of the extra screed.
Neither would I want to be the bloke in the flat below. It sounds highly dangerous to me.
Rob Graham
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That ain't necessarily so. As a bridge engineer I have designed concrete beams and decks with pre-camber. This means the deck is cast as an upward parabolic curve. The self weight of the slab, and the other dead loads, i.e. road surfacing materials, will then pull the slab/beam to just about flat. The live loads on the slab, i,e, traffic will cause it to sag, or flex downwards, but this will recover, when the live loads are gone i.e. when the truck has driven over the bridge.
However, I am talking about reinforced concrete!

minimum crack widths allowed. As to design with zero cracking is expensive and over the top depending on the environment the concrete and more importantly the embedded reinforcing steel is exposed to.

Absolutetly! On this I wholeheartedly agree. What is the construction? Is it a reinforced or mass (non reinforced) slab, or is the slab supported on joists. (I cant picture this really) The most important place to look for cracking is in the tension face of the concrete. Which in this case is the underside. Go and talk to your neighbour below. It is certainly in their interests to get to the bottom of this.
If this sag has always been there it is entirely possible it was cast that way and is therefore not a problem. If it has appeared recently, I would suggest urgent action to find the cause and not treat the symptoms is the most appropriate.....along with moving out until it's fixed!

I'm slightly less concerned, but Rob is right to er on the side of caution.
Al

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Yes, I have to say that I was not talking about reinforced concrete. Obviously the reinforcing rods will prevent a lot of the problems, but to the OP I wools say that he ought to keep off it until he knows the full story.
Rob
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You may have hit the nail on the head .... it occurs to me that joists in other parts of the house had to be replaced when I got the house due to woodworm, they never checked the kitchen ones as the floor is concrete, but there was woodworm in the floorboards in the living room which leads to the kitchen. I will mention that in the morning when they arrive to look at it.
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I've got a feeling you might be moving very soon.. (and the guy below too)..
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Yes, vertically downwards.
Rob
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"Mandie @k@ Zepherous" wrote:

If the kitchen floor really is breaking up you could ask the advice of the building control officer at your local council as this is a structural safety/danger issue.
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Hi
GET OUT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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Phil Anthropist wrote:

I worked in a 70s built office with solid concrete floors that sagged between the concrete uprights. It was noticable if you walked from one upright to the next and any large cabinets tended to lean towards each other visibly umless one side was raised a few millimeters
Engineers checked it and decided it was safe but placed weight limits on the floors. The building is still up five years later, I beleive the new occupants put a wooden subcloor down to get rid of the sag.
You obviously need a structural engineer to check it out, A good landlord would have done this and should have a report to show you! If he hasn't call the council.
Mike
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The council are my landlords :-( I wouldn't reckon on getting an unbiased report.
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Mandie @k@ Zepherous wrote:

you a copy complete with all kinds of initials! If they can't contact your local councilor.
Mike
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Mandie @k@ Zepherous wrote:

The whole point of this exercise is why was the floor concreted over in the first place? I find it very odd to have a concrete layer over floorboards and then boarded over, in an upstairs flat/room. Surely this might indicate that the floor itself is in a state of repair?
--
Sir Benjamin Middlethwaite




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to my knowledge the layers on my floor are: concrete then a layer of floor tiles, when I moved in the tiles were covered in glue and the remainder of a carpet which had been glued down. I complained about this and they came and put hardboard over the top and then more floor tiles. All the floors in the house are floor boards with the exception of the kitchen and bathroom which are both concrete.
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The joiner was here this morning to lift the hardboard and other layers (what a mess) he hasn't lifted it all just the main area that is sagging by around 2 inches an area of around 4x4 feet. He tells me that there are no joists and that it is concrete beams. I am waiting for the building inspector to visit and give his opinion of what is to be done allthough the joiner says they will most likely just screed it as the houses are due for demolition within the next couple of years anyway due to subsidance.
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Mandie @k@ Zepherous wrote:

Thanks for the update :-)
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Zepherous wrote:

OK, so what really happened? What have they decided?
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