Author Topic: We have cracks in the foundations of our new home  (Read 3990 times)

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Carol36

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We have cracks in the foundations of our new home
« on: August 09, 2014, 08:27:57 am »
I am wondering if anyone  could you give me some advice on shrinkage cracks in my foundations. Nobody else has them but they are all over ours.
We are not supposed to go onto the site but it's across the road and not really secured, are they something to worry about, should I mention it to Persimmon?

Thanks


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Re: We have cracks in the foundations of our new home
« Reply #1 on: August 09, 2014, 08:59:01 am »
Your foundations probably only have surface hairline cracks, especially if they are the "trench fill" type and even more so if too much water was added when they were poured.   Obviously on hot days the concrete dries out too quick causing it to shrink and crack.   However it is likely to be just surface cracking. 
Remember the  NHBC Buildmark warranty, such as it is,  covers structural defects for 10 years. 

As general rule, if you can get a 10p coin in the crack it would probably need further investigation.
The NHBC concrete mix standard was changed a few years ago.  It is currently C10 also known as GEN1.
Both of these mixes are used as a foundation or footing mix for non-load bearing walls, garden walls up to 900mm high and foundation mixes for house construction.
Classed as a "wet lean-mix" it has a strength of 10N and should contain a minimum cement ratio of 170kg/m3 Concrete for foundations should also comply with BS 8500 and  BS EN 206.

The C10/GEN1 mix is weaker than the previous 20N standard it replaces so any water added or anything else could be more likely to result in potential problems.  If you are worried write [e-mail] the house builder and the NHBC now, whilst the foundations can be easily checked.

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