Concrete floor settlement

[Hazel80]

Hi, we have a problem with our 3bed bungalow, 1000sq ft living space with breeze block walls. Having had some internal cracks looked at by our loss adjuster, we have movement of our concrete slab floor due to poor consolidation of subbase. Unfortunately our insurance does not cover this. He has suggested we use a company to stablise the slab by injecting polymer through bore holes.
Our loss adjuster has suggested we are on cohesive soil, but did not say that that was a factor in the problem. We also have a Oak tree 5m from our property - again he did not say that that was a factor.
Should we have go to the expense of having soil tests? If so can anyone recommend a company who is reasonably priced.
Does anyone have any knowledge of this type of repair, and also recommend a company for quotes.
Any help/advice on our situation would be gratefully received - this has been a very expensive shock to us! Thank-you

 

[Shytalkz]

Hi Hazel

Firstly, did the loss adjuster just do a visual inspection and make this determination? If so, then become his manager and make yourself a fortune, for he is truly blessed with xray vision. In all seriousness, there are several reasons as to why slabs will settle, but to positively determine causation , it requires exploratory excavations through the slab, to see what's underneath.

If he said consolidation to you, he actually meant compaction of poorly laid sub base material under the slab: consolidation is the removal of pore water from a soil, which is unlikely from the pressure exerted by a domestic floor slab.

If it's sat on an inadequately stripped site and there is vegetable matter and topsoil remaining under the slab, then pumping grout underneath will do nothing other than provide a short term fix.

The reason that you claim was binned by insurers is that slabs are only covered if the structure of the building is damaged by the same cause at the same time. The trees can be ruled out as a cause as if it was clay shrinkage, it would be reasonable to expect the external walls between the tree and area of slab movement to have moved as well.

Have a closer look at the exterior walls of the property and see if there is any distortion or cracking in the vicinity of where the slab has gone down, such that you could go back to the adjuster and get him to revisit and reconsider.

Without any movement to the superstructure, you are on your own, regardless of causation - with the exception of a water leak from supply pipes or heating pipework. Did he positively rule this out and, of so, how?

The next step is then to determine the reason for the movement. That needs small holes being excavated to have a look underneath the slab, digging through the sub base into the underlying soils.

If the sub base is poorly graded and obviously loose and there's no topsoil or loose soft soil underneath that, then gradual compaction is the likely cause of the movement. If your house dates from the 60s or early 70s, then the movement has probably reached the maximum extent, as the sub base material can only compact so much. In which case, all you need to do is relevel the floor using levelling compound or by rescreeding.

If the soils under the sub base are organic then, without transferring the slab load through this, movement will continue and pumping cementitious grout underneath will only make it worse, by increasing the loading to the soft soil. In this instance, mini-piling - effectively making the slab like a table with many legs - would probably be needed, in conjunction with grouting.

If it's a case of a water leak then firstly that needs repairing and only if that has caused extensive voiding, would that possibly need grouting.

Personally, I would only use either cementitious or polymer grouting as an option for movement to both slab and foundations: most of the time, it is not needed for a slab, unless in conjunction with mini-piling over organic soils as mentioned above.

The way insurance used to work was that the burden of proof was upon the insured to prove a loss under an insured peril. That has changed gradually over the years and has become less defined where the loss adjuster also acts as the engineer and project manages the claim for insurers. I would presume that you have one such company for your claim (CL?). They will try and get away with the bare minimum, but a visual inspection is not proof positive that there is no valid claim under the policy (unlikely but not definitely the case), in which case go back to them and get them to do a proper investigation. If you get no joy there, go directly to insurers: you do not have to deal with the loss adjuster.

You are also entitled to have your own engineer investigate and, if he establishes a cause that falls under the terms of your policy, then his fees form part of that claim. I would certainly advocate this if no investigation has been carried out, as at least you will know, for a fraction of the cost, if what the adjuster has said to you is worthwhile spending your money on.

And, if you decide to go for grouting, Roger Bullivants do cementitious grouting; Uretek do polymer grouting.

HTH

 

[Hazel80]

Thanks for info - we have carefully checked our external walls and they do all appear in very good condition, excepting our porch entrance has a crack very low down and quite small, this has been attributed to the slab. Our property was built on a a small spinney which had quite a few birches and other minor trees on it which were cut down prior to build. We used a small local builder. We noticed some cracking very early on, i.e. 3/4 years but was told it was settlement and happens in new homes, this was repaired by builder but that crack subsequently reapeared after the NHBC had finished. The cracks have increased in amount and size significantly over the last 2/3 years. We have a lot of trees/vegetation surrounding us, 4 oaks at the rear within approx 22m away. The water table is quite high here and we regularly have pools of water in our garden. Our footings were 1m depth on 3 exterior walls but 3m depth alongside the oaktree at the front which is 5m away.
The loss adjuster was 'infront' and has sent us a very fancy booklet- it all looks very professional and what I can't beleive is that they can state this cause as a fact, but it may not be the case. Surely if we go ahead on his recommendation and it does not work then they are liable? It is only through some reading ourselves that we are questioning his diagnosis?
Looks like we may have to pay for site investigation, we live in the Midlands do you have any recommendations as to whom we may contact (hopefully someone who does not charge a fortune?!?) Thanks again for your help. Oh and we have not evidence of damp in the home, would this be the case if we had a leak?, and the property was built in 1985.

 

[Shytalkz]

If your house is on clay and occupies the site of previous trees, then, rom the age of the property, there should be heave protection under the slab, as the clay will have gradually expanded as it rehydrated, as there are no longer any trees to withdraw the moisture. As the moisture contents in clays change, the volume increases or decreases; when it varies significantly either side of the moisture content that existed at the time of construction, then the building can suffer from heave or subsidence, depending on whether it's plus or minus of the prevailing m/c.

However, the fact that there is no significant cracking to the external walls suggests that it might be a case of compaction of the sub-base material, but only if the floor slab was not designed as suspended in situ reinforced concrete, or precast pot and beam.

Whatever the cause, a definitive answer can not be given from a visual inspection; nor can the floor construction be positively determined. I know the adjusters whom you mean, from previous dealings with them, they are not a company that impresses me greatly, tbh.

Before you spend any money on remediation, you do need an SE to do an intrusive investigation. But firstly, I would go back to IFS and tell them that there's no way that they could have made a positive diagnosis from a visual inspection and to do it properly.

The cracks: are they getting progressively wider, or are they there during the summer and less so in the winter; or is the movement closing up and popping the previous repairs?

 

[Hazel80]

Thanks. The cracks are evident at all times they are creeping further along walls. They do not close up, and we are getting spur cracks from the originals. They are horizontal and reach the floor before they reach the ceiling. They are wider at the bottom and middle. One interesting fact is that the engineer said that we have a particularly large slab and they would now build it using the 'beam' method you are suggesting. We are not even certain whether it was reinforced. Strange thing is that where our foundations are 3m we do not have any movement it is around the centre of the home and towards front/back. Both sides interior walls are crack free?

 

[Shytalkz]

You sure it was actually an engineer, or a loss adjuster masquerading as one?

What he's saying, I presume, is that it's a ground-bearing slab - again, how could he tell what construction it is without doing any investigation?

I find the use of such construction hard to believe, as the design standards have not changed that greatly over the past 20-odd years for clay sites and, with tree removal from the building footprint, heave would be a consideration (espesh with NHBC involvement), for which a ground-bearing slab is a no-no. Pot and beam was around back then as well, it's not a new technique!

Have the cracks only recently re-started, or has this been an ongoing thing since the property was constructed? Wider at the bottom suggests the slab is going down though. But it begs the question as to why, if this is only a relatively recent occurrence. Are the cracks near the airing cupboard, boiler pipes, central heating pipes, incoming water supply pipes? Do they run upwards and towards the outside walls, or towards the centre of the property?

 

[^woody^]

Loss adjusters are as clueless as an empty bag of clues

They will say anything to try and justify not paying anything out.

Ask him if he is qualified to comment on structural matters, and then ask him how he can be so sure of his statement from a visual inspection.

Then ask if he (or the insurer) wants to arrange proper tests or if you should .... and re-charge to cost to them - mention that you know a really good engineer but he is sooooo expensive

 

[Hazel80]

Thanks both. Just to clarify, our cracks are wider at bottom than the top, some start from a corner and run diagonally up the wall towards the centre of the property. We also have a couple of newish cracks that are horizontal and go from one door opening across to the next. It does give the impression that the floor has dropped both at the front of the house and also at the back of the house. Through the centre of the bungalow we have aload bearing wall which was built on approx 450m (mini foundation) and we have no cracks on this wall. Hall crack 1 runs behind radiator, Hall crack 2 is on opposite side of wall. Bedroom 1 crack runs through adjacent wall to radiator. Bedroom 2 crack runs behind radiator. We are now having other hairline cracks appearing. They seem as though they are due to the dropping floor line. We are going to go back to the loss adjustor/engineer to ask for further investigation, but would welcome any names of site investigation people in case we do have to do this privately. Thank you both

 

[Shytalkz]

From your description of the cracks, it's clearly a dropping floor problem, but the reason has not been positively established.

I'm with Woodster on the general capability of adjusters and afaiaa, IFS have surveyors, rather than structural engineers, on their payroll. I'm more than aware of blithe comments made by them in their determination of causation, invariably of the non-insured variety.

Keep kicking their back doors in and demand a proper, invasive investigation - at least that way, even if it's not due to an insured peril, you won't have to pay for the cost of the investigation.

If you get nowhere, raise a complaint with insurers - they get very jumpy when the insured kicks off (unless it's fraud or arson, which is fair enough) and it's amazing to see how far they will bend to appease...sometimes, totally ridiculously, where it's obviously a scam. I can think of one where the odds were that a guy torched his building, yet, by complaining, he got me kicked off, the loss adjuster kicked off, the contractor kicked off...yet who was the common denominator here? Unfortunately, forensics were not able to say conclusively what had happened, although their gut feelings were exactly the same as everyone else's. He got £400k out of insurers over that. Disgusting.

Any local SE to you should be able to do an investigation for you if that's the way that you want to go. Expect a fee in the order of £900-1200 plus VAT, depending on how much they have to do, lab analysis etc.

In the meantime, keep looking for cracks on the external walls (inside or out, it doesn't matter) to link the movement .

 

[joe-90]

Well I'm not an SE but in my time I've seen this sort of problem caused by drains. Leaky drains. That's the only time I've seen it. My advice to you (before you start filling the SEs pockets with wads of cash), is that you try a few things yourself. Take the cover off your inspection chamber (that big square lid in the garden somewhere) then flush the toilet and try to gauge if the same amount of water is passing throguh. Do the same with any drain gully etc that you can find around the place.

Listen to your water meter, does it 'tick' when no water is turned on?

If so you may have a leak under the floor.

Do you ever hear your central heating header tank filling for no reason? Again, it could be a leak in a pipe under the concrete.

Do you have a friendly builder/DIYer that can drill a few inspection holes in the floor with an SDS drill where it is sinking? The last one I drilled into had a complete void underneath it, where a leaky drain had somehow made the subsoil shrink.

Stick a piece of metal rod down your inspection holes - does it feel soft? Does it come back up wet?

These tests will cost virtually nothing yet could prove everything. You only have to pay a £50 excess if it is a leaky drain and the whole lot will be fixed. Worth a go eh?

 

[Shytalkz]

Guiseppe, if you read above I said to go back to the adjusters and insist on a proper investigation in the first instance - which would be at insurer's cost, regardless of outcome.

Ditto comment on water-bearing services, although you have expanded on this somewhat. Even in the right vein too, you're learning... .

 

[joe-90]

I've read your posts - and they are good posts. Credit where credit is due.

 

[Shytalkz]

Bless you sweetheart xxxx - yours was the perfect mix of information, yet not too high-brow for the layperson, I have to say.

 

[joe-90]

Is that a roundabout way of saying I'm thick?

 

[Shytalkz]

Cor blimey, I give you a compliment and you think that I'm ripping the proverbial! I was not being sarky or nuffink, honest.

Come here and have a hug, is all this doom and gloom getting to you?