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french drain specialist in london

(9 Posts)
Whoatemyporridge Fri 13-Jan-17 14:02:35

hello,
i wonder if someone can recommend a specialist in french drain installing in London. it seems to be not an easy task to find one.
We live in edwardian house on a ground floor and we've been on a "damp fighting route" for long enough. After long research it seems like french drain seems to be an answer. At least i would like to know its cost comparing with the usual chemical injections and replacing the old plaster.
I would appreciate any comments/ notes of experience and contacts! thanks!

SorryNotSorry Fri 13-Jan-17 15:05:23

No help just looking for the same, but Victorian house in Hertfordshire.

Will watch thread with interest

PigletJohn Fri 13-Jan-17 16:22:43

I didn't know there were specialists. It is basically just a trench full of gravel or cobbles, with a perforated pipe at the bottom collecting water and taking it to a soakaway or drain (you are not allowed to put groundwater into a sewer).

My neighbour had his house encircled in this way, he had a largish cobble fill, which is less easily choked with mud and dirt.

I sae this vid by chance, which is a small-scale DIY job. It does show how the wall started to dry out as soon as he dug out and exposed the bricks to the air. He is wrongly and illegally draining to a sewer. His house suffered from raised ground level (concreted) all round the house, which obstructed airbricks, encouraged rainsplash onto the walls, and probably bridged the DPC (if any). This is sadly very common, where homeowners and builders have actually done things to cause damp. You can also see traces of the useless chemical injection that was previously done, instead or correcting the cause of damp.

youtu.be/3PiVmauxQTA

Whoatemyporridge Fri 13-Jan-17 22:02:38

thanks PigletJohn. its very helpful and once again i'm persuaded to stay away from DPC. +1
The video did make me wonder.... We have a similar rendered wall where the actual 'rising' damp appears. its the only rendered wall which looks out in our neighbours garden (unfortunately) and we never actually see it. Other side of the house is a brick wall, its nice and dry and has never developed any damp so far.
Today I inspected the 'troubled' wall myself, and i found a flower bed all along the wall, which is probably attracting more moisture. There were big wet patches on the wall where i pushed the soil away (see attached images). i didn't see see any foundation bricks. I suppose they re deep down..
well, and I wouldn't call it small DIY job for us personally smile And regarding specialists, i spoke to some people on the phone today. They vaguely recommended me to pay for a survey first, then calculated the estimate starting point from 1.5k.

just to clarify did your neighbour use the same technique with the pipe or were the pebbles an alternative?

thanks again!

PigletJohn Fri 13-Jan-17 22:49:57

he has a large Victorian house, and the cellar suffers water on the floor during some high tides. Although we are about half a mile inland, there is hardly any rise.

His French Drain (named after Mr French who wrote about it, not the country) IIRC does not have a pipe at the bottom, but it prevented excess water lying against the wall (cobbles do not permit capillary movement as the gaps are too big). But I think it is usual to have a pipe to lead the water away, otherwise the trench might fill up with water like a moat, which would not be what you want.

It's possible he had it led into a soakaway under the garden somewhere. The trench would have passed his numerous downpipes from the gutters. Or there might be a culvert (there are lots round here). He does not have a stream, the nearest one is about a hundred yards away.

In your picture, it certainly looks like the wet ground is wetting the wall. A cement plinth or render on a wall is said to encourage damp, and to inhibit the bricks drying out, and also it will bridge the DPC (if any). You might have the same problem as the man in the video.

PigletJohn Fri 13-Jan-17 22:56:46

BTW when I look at wet walls, if the bricks are exposed, the wet never seems to extend more than two courses above the wet ground. I think this might be because water can rise through a brick by capillarity, or through mortar/concrete, but in some way is prevented from crossing the boundary between the materials when the pores are of different sizes. In the vid I saw the same thing. I get it in my house too. I doubt it can be pure chance.

If you search on "rising damp" you will find experiments on brick wall built in water tanks, and photos of brick bridges in rivers, showing something similar.

Whoatemyporridge Fri 13-Jan-17 23:55:59

thanks again for such a thorough response. i'm very grateful

I am no specialist at all but as as i see it there is a problem with WHERE the water would lead to... I am not sure.
as i mentioned before, the wall is in my neighbours garden and its already a lot to ask, all that digging around the garden and then to making a 'soakaway'... And there is absolutely no way we could lead the trench to my garden round the corner as there is another neighbours garden between us . thats why the idea of cobbles looks so attractive.

In Russia (where i'm originally from) the houses traditionally are build with so called "blind area" or 'paved path' around the building. Apart from a purely aesthetic function it has a definite practical sense to protect the foundation of the house from moisture penetrating the sedimentary and uneven caving.

it literally means (in summary): layers of sand, pebbles and cement on top of each other, covered with concrete slabs or cobbles creating a protective layer agains the walls and the foundation.
i wonder if that would be the thing to do to avoid the trench and a pipe.. though it might be a specific thing for cold winter countries', i am not sure. i couldn't find any english written info about it..

PigletJohn Sat 14-Jan-17 00:33:22

if the wall is the border with your neighbours garden, I doubt they will want you to do anything much there. It does no good to try to coat the underground face of the wall with waterproof paint, because water will penetrate from underneath. I would be thinking about removing the render from the wall, at least up to 200mm above ground level, and repairing the pointing and any cracks. If you can persuade the neighbours to let you lower their flowerbed it would help, but you can't trust them, or future owners, not to heap earth up against it again.

if it is a wooden floor in your house, you have the possibility to ventilate the void under the floor, and the inside face of the wall, using airbricks on the front and back of the house sufficient to get a good flow of air.

There is a technique of using a dimpled plastic membrane against the wall, the dimples hold it away from contact and let water drain downwards. It is not common but some companies dealing with damp cellars use it.

If the neighbours ever want to lay a path or drive, you could offer to contribute to the cost on the condition that you can provide drainage, and slope it away from your house to assist run-off. And preferably lower the height below your floor level (and dpc, if any).

Whoatemyporridge Sat 14-Jan-17 07:54:11

thanks PigletJohn! i will look into all of these options (i may come back to you with further questions) smile

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