Renovating a French drain

[Ushy M]

Hello folks, I posted on this subject some time time ago and got some useful advice - we've finally got around to doing something about it. We have a 350 year old stone and thatch house, with the gable end in the churchyard. The ground levels are, for obvious reasons higher on the churchard side and we've been advised to dig a French drain to equalise this. Having had an exploratory dig, we've found that someone has already dug a drain which goes down to the foundation stones. They appear to have applied bitumen paint to the house wall at sometime in the past and have filled the drain with common half bricks (which are damp).

The bitumen coating is peeling away and we think pointless to try and remove?

The external house wall appears pretty dry, there is however, no land drain under the rubble filling and we intend to install one as much to allow air in through the bottom as to channel water away. We can lead this away to a clear exit point. We've been advised by a groundworks contractor that the rubble or some 20mm shingle would be an adequate filling (tho we think cobbles might be better). The earth side of the hole is lined with geotex, which seems to be doing its job OK.

Inside the house, the wall has been replastered with modern gypsum, which we'll remove and allow to breathe before replastering with lime. Grateful for any views as to whether this seems like a good plan - and whether anyone has any better ideas?

 

[Gervase]

It sounds as though you've got the situation well in hand.
Don't worry too much about the bitumen; water will tend to take the easiest route, and that will be via the land drain, so it's unlikely that the wall will be saturated enough to allow the bitumen to trap large amounts.
Shingle is fine as a fill - ideally it should be washed to remove fine stuff, but a layer of geotex over the land drain will help stop clogging. If the drain exit can allow for rodding out that's an advantage, as you will always get some silting which, over time, can impair its efficiency. If you bed the land drain on some pea gravel you can ensure that it runs absolutely straight and can engineer the fall more easily, which will prevent low spots which might be prone to silting.

 

[Ushy M]

Thanks Gervase, off to buy the land drain now - spent yesterday morning washing cobbles - oddly therapeutic. Will get onto the job - if it ever stops pi**ing down here!

 

[inwood]

Just thought you might like a bit of reassurance that the drain will improve matters - when I discussed this with my CO I was slightly sceptical.

I probably live fairly close to you (Old Stratford) but I'm renovating an old farmhouse in Irthlingborough. The internal floor level of the kitchen, pantry and part of the sitting room in this house is in places about 4 foot below the external ground level. When I bought the house the floors of the kitchen and pantry were constantly wet with damp.

I've used various measures to help manage the damp:
1. Removed cement and gypsum plasters from the internal walls and replaced with haired lime plaster (which is now dry). If you're going to lime plaster below external ground level use an NHL (2 or 3.5) lime or gauge a lime putty with metastar otherwise it just won't set (I re-pointed a small area in the chimney with ungauged lime putty below ground level and it's still soft to the touch three months later!)
2. Dug out the floors (which were originally ceramic and brick tiles on earth) and replaced these with limecrete floors before replacing the tiles.
3. Installed a french drain (actually in my case a 100mm perforated land drain wrapped in geotextile) and then installed to the base of the trench and covered in pea gravel.

I have to say I'm very pleased with the results. The floors and walls are now dry despite the higher ground level (and all our recent rain) and the limecrete seems to be doing it's job. In fact there was an old bit of cement as a hearth in the kitchen fireplace - this stayed constantly damp, yet right next to it the limecrete is dry.

 

[Ushy M]

Thanks for that - the tip re. the lime putty is really useful. - and glad to hear you're all dry now!

 

[Lime]

In fact there was an old bit of cement as a hearth in the kitchen fireplace - this stayed constantly damp, yet right next to it the limecrete is dry.

Proof if any were needed that lime is better than cement in older houses.