Forum: Site Works
Topic: House Foundations
started by: lizzy

Posted by lizzy on 24 June 2004,13:31
Excellent site by the way!

We are currently looking at having a new driveway installed.  Not sure at this point what type, probably patterned concrete.  My question relates more to the house.

Our foundations are the concrete raft type.  The problem is the foundations extend beyond the walls of the house by approx. 1yd.  The damp proof course on the house is only 2 bricks above the raft.  I'm trying to find out whether it would be possible to cut-away some the raft so the new driveway can go closer to the side of the house.  Our neighbours all have left the raft showing or gone over the top of it and reduced the height of the damp proof course to a stupidly short height, neither are a good solution in my mind.

Would we need to involve a structural engineer to gain an answer?

Thanks in advance.

Posted by alan ditchfield on 24 June 2004,23:49
The concrete raft is there for a reason do not cut it away,  although this post will probably leave me more unpopular with the people on this forum than i allready am, i would never
recommend imprinted concrete  as a suitable surface as it does nothing but break up and look like concrete that is meant to look like stone and never does .  ps instead of telling me that your producty lasts without breaking down the middle allow your customers to answer.  ie no answer from people who have anything to gain or who want to look clever by reading  statistics on certain web sites but really have no on site experience as it is so obvious when you try.  you come out with loads off AZmZSoS.S and some other technical shite.txesm>s to try and make the people who are on site allday look incompetant.
Posted by lizzy on 25 June 2004,08:27
Thanks for your input Alan.  Does anybody else have an 'opinion'?
Posted by Guest on 25 June 2004,12:24
I'm with Alan for his first paragraph - you should never, ever cut into a raft foundation. It's been made the size it is for a purpose and breaking into it is likely to end in tears, as you risk exposing steel rebar, or even inducing a crack. Leave it alone.

And I'm with Alan for the first part of his second paragraph, in sharing a dislike for PIC - as I say somewhere on the main site, I get more complaints about PIC than all the other forms of paving combined, and that includes Tinker-laid tarmac! When it's done properly, it can be almost attrcative, but so much of it is laid by incompetent buffons who make ludicrous and unsubstantiated claims about the stuff, and then wonder why their clients end up disappointed.

However, Alan loses me completely towards the end of his post - I've no idea what he's on about, and I'll just have to put it down to an adverse reaction to the footy result last night.

Care to shed any light on the thought processes behind your troubled stream of consciousness, Alan?

Anyway, back to the problem: going off what you've told us, Lizzy, I'd suggest using a gravel as a surface dressing over the shallow raft. You could use a loose dressing, one of the self-binding gravels, or if you're looking for summat with a bit of class and style, one of the resin products.

I'd be reluctant to cast PIC over the raft, but, if that's what you really want, then I'd insist on there being a break layer between raft and PIC, say a 25-50mm layer of sand or similar, so that, when you come to realise what a disastrous mistake was the PIC, breaking it out with a jack-hammer isn't likely to damage the raft.  :)

Posted by lizzy on 25 June 2004,13:32
Ok thanks Tony.  I was just wondering if it was possible to somehow  'slice' off the top few inches of the raft to give some extra scope.  It would be a very long job with a stihl saw, but couldn't see any other way round it.  That way we'd be replacing the concrete that was 'sliced' off with the PIC.

Probably talking rubbish!

Posted by Guest on 25 June 2004,17:55
No - because you're likely to expose the steel rebar in the raft, which means disaster: it could actually invalidate your buildings insurance!

If the steel reinforcement in the raft foundation is exposed to the atmosphere, it will rust, expand, deteriorate and de-bond from the concrete surround. If you then cover up with an inferior PIC concnrete, which is prepared to be a paved surface, not a structural component, then groundwater may be able to get into the construction joint (the plane of contact between old and new concrete) and continue to attack the rebar.

As I said before, you just don't interfere with foundations.  :)

Posted by alan ditchfield on 25 June 2004,19:05
not too sure on that post myself its more like an adverse reaction to 10+Stellas at the boozer,  i think i was trying to say i dont care how hard you try to convince me i am never going to be a fan of impr conc.

(Edited by alan ditchfield at 11:35 pm on June 25, 2004)

Posted by Guest on 26 June 2004,13:15
I'm not going to try to convince you!

I admit to being completely and utterly biased against PIC, not because it's a bad idea or unattractive, but because all too often it is sold under false pretences, it is normally laid by people with insufficient training, and some of the contracts that are imposed upon clients are the most one-sided, unfair documents it's possible to get away with under English law.

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