New Slab or not New Slab?

[Antparker]

Good Morning Guys n girls,

 

So this is my first post here, and straight in with some questions I’m afraid !

 

I’m in the process of purchasing my first residential property at the moment, it’s a semi detached bungalow here in essex, the construction is the perimeter walls are on a deep footing, while the internal ‘slab’ is a separate section of concrete (Not unusual I understand)

 

My issue is that the slab has ‘settled’ over time and has been brought back into place using expanded resin injected under the slab.

 The settling was as much as 30mm in places, and was not level throughout the building. Some parts 30mm some parts just 5 or 6, some none at all.

The Company who injected the resin offer a 20 year warranty for any faults due to the shrinkage of their material, however that doesn't take too much reading into... 

 

My issue is this:

 

1. we don’t know why it settled in the first place and how long it will take to settle again (I think it’s a question of when not if?)
2. Did the settling cause the DPM to tear or become broken- are we going to get damp issues in the future.

       C.  We don’t know if the same settling will eventually happen with the rest of the building?

 

So the question is this:

 

How risky is this.

How would be the best way to repair it ‘properly’- I assume the only solution is to break up the entire slab and either replace with a new poured floor with deeper support underneath, or with a suspended wooden floor.

If you were to do this, what would you do to support the supporting spine wall – I guess the spine wall just sits on the slab at the moment, if the slab is broken away, how do we support the spine wall?

Similarly, when digging the slab out what do we do to support the perimeter walls / foundations of the building

 

I’m an engineer by trade and not afraid to get my hands dirty, but just want to know how much would be involved, should the need arise to start digging out the existing slab

 

Interested to hear some thoughts an opinions of people who probably know more about this than I do….

 

Many Thanks

[Mr Punter]

Greetings @Antparker and welcome.

 

A few qs may help us with suggestions:

 

When was the house built?

 

Is it on clay soil?

 

Are there any cracks in the walls, or is the "only" issue the floor?

 

Does the slab have any cracks through it? (You will need to remove floor coverings in any case)

 

It may be that all the ground floor walls are built off a proper foundation and the floor is more than one concrete slab that have settled.

[Antparker]

Hi @Mr Punter, 

 

Thanks for your quick response - Ill do my best to answer your questions: 

 

The house was built around 1960 (according to the mortgage info).

 

Clay soil – Yes I believe so.

 

No visible cracks in any walls, although I’m going to look much harder on my second visit!

 

The slab had no visible cracks, however floor coverings are down, and one room oddly had brand new modern flooring, when the rest of the house is in 70’s/80’s décor….

 

I’m not sure if the floor is multiple slabs, the impression I get is that it’s a single slab and the walls sit on this, when the slab sank a crack was evident underneath the spine wall – which I guess means this isn’t on a proper foundation.

 

I Hope this helps.

[Mr Punter]

It may be worth seeing if you can get any information from neighbours if they have a similar property.

 

For a proper job you may need to:

remove the existing slab

excavate soil beneath

underpin the spine wall

install a new suspended floor (beam & block or timber)

 

The remedial option chosen before failed and will probably fail again.

 

You could just screed the worst bits and hope for the best.

[Antparker]

thanks Mr Punter - so i checked with the neighbours and no one else in the area has had anything similar. Even the attached bungalow next door has not seen anything remotely similar. 

 

Very odd. 

 

I agree that one option would be to dig it all out and go again as you say, its just weather or not to get involved in this level of work and cost so early on in the project i guess! 

 

Many Thanks 

[Ferdinand]

Call local Building Control and see if they know anything.

 

You may need to be judicious as they auto-publish less information than Planning.

 

Edited April 23, 2019 by Ferdinand