Slate as a damp-proof on a retaining wall?

[Adrian]

We live on a hill, with one side of a '70s extension butting straight up to the bottom end of a neighbour's garden. The difference in levels is about 4', so there's a fair bit of good soggy soil stuck right up against the (unrendered) brickwork.

In the time we've been here, the side of the house has been hidden by fairly thick shrubbery, but that's recently been removed, and they're busy taking the remaining roots out.

So - I've had a little look, to see what that wall actually looks like. And I don't much like it.

The damp-proofing between the earth and the brickwork seems to consist solely of some sheets of slate. There was similar at the front of the extension, behind render, and it seemed to be doing a great job of holding water... in.

The inside of the wall's been hidden behind some very, very full bookcases for a few years, but there was no sign of any damp penetrating through before they went in. But, equally, there was no sign at the front, either.

Here's some pics...

- your thoughts?

[Adrian]

Adrian gurgled happily, sounding much like they were saying:

I should add that they're planning on putting something there - fencing, probably - so it's a bit now-or-never if something does need to be done.

There's also about 4 or 5 metres, round the corner, where the back of the extension butts onto the side of another garden. So _please_ say "No, it's fine"...

[Steve Firth]

If you're planning to do something to improve damp proofing and you need to do it quick and relatively cheap then I suggest having a look at Delta mebranes products.

I'd give a URL for their site, but it appears that it has become host to malware.

The Canadian site seems OK, so you could get an idea of the product application there:

[Bruce]

It looks like an ideal application for a French drain with a porous pipe at the bottom, with the outflow from the pipe connected to the drainage system.

[Big Grin]

Agreed Bruce - but if possible, ending the porous pipe in a soakaway pit (or rat-trap soakaway chamber) some distance away may be preferable (and easier) to having to build a 'solids' interceptor trap for the porous pipe before the water goes into the main drainage system.

Big Grin

[Bruce]

Agreed.

[Dave Liquorice]

If it ain't broke don't fix it?

70's built so presumably a cavity wall, the outer leaf may be damp but provided it's not getting through to the inside why worry?

[meow2222]

bitumen... quick, easy, cheap, effective.

NT

[Adrian]

"Dave Liquorice" gurgled happily, sounding much like they were saying:

I like that answer...

[Adrian]

Bruce gurgled happily, sounding much like they were saying:

[Adrian]

[e-mail] gurgled happily, sounding much like they were saying:

...and I like that answer...

So - get the earth away from the wall, clear the slate out, paint a good thick coat of bitumen onto the brick, then earth back in and forget about it?

[Clot]

No, a bit more work than that. Bitumen, yes. Then two rows of slate rather than the single that seems to be in place at the moment. The slate will act as a physical barrier to prevent spades, forks, etc. damaging the bitumen seal.

Ideally, I would prefer the soil being removed from the wall down below the DPC but I think you are trying to avoid this best option!

[Adrian]

"Clot" gurgled happily, sounding much like they were saying:

Ah, gotcha.

Totally, permanently? My preference doesn't hugely come into it - the house wall is _right_ on the boundary. The mortal remains of the old fence is visible in the first pic...

[Hugo Nebula]

On 22 Feb 2009 21:30:45 GMT, a certain chimpanzee, Adrian randomly hit the keyboard and produced:

In a properly-constructed extension where the floor level is below ground, then it should have been constructed as a basement, with a tanking membrane or waterproof render up the walls, to a cavity tray above the external ground level, and linked to the membrane under the floor. The only external sign would be weepholes in the mortar (but not always). Do you know if you *haven't* got this?

[Adrian]

Hugo Nebula gurgled happily, sounding much like they were saying:

Not a clue.

[Clot]

Appreciated. It depends on how you get on with the neighbours!

[Adrian]

"Clot" gurgled happily, sounding much like they were saying:

Oh, they're lovely people - but suggesting appropriating more than an inch or two of garden probably won't go down well...

[mail]

pics...

> So - your thoughts?

Dear Adrian This is clearly an amateur job and the presence of slate is not a damp- proof course or membrane any more than were you to cut up some polythene sheets into A$ size and put them up in the same pattern How would you feel about a sheet of bituthene with similar holes and slits in it? Most people have made a sensible suggestion as to what to do Persoally, if it were mine and costs were to be considered I would opt for both a land drain or even just fill the hole with pea shingle together with either a render splatter dash (1:1 Sika No 1 times 2) or simply a sheet of poly membrane to act as a physical barrier to reduce the amount of transfer of damp All should be done to 150 below the interal floor level Chris