Damp on Internal Walls - treatment

Doozergirl

Not like me to start a thread!

We are working on a project in a typical Central London 3/4 storey terrace where the bottom floor is below street level. although it has stairs leading down at the front and a garden at the back which means it isn't strictly a true basement. I guess that the water table is nearer than it would be although we've already dug to 1 metre outside and it is dry.

Having taken the internal walls back to brick, the bottom floor has been rendered internally - previous issues I'm sure! There were also tide marks on the walls through the render at quite high level before the skim was removed. I think the walls are dryer than they were (just from removing the render), but this is a really expensive house and it will be sold, so there is no opportunity to wait and see.

To my mind, if you have a concrete floor, then even if you use lime plaster on the walls there is still potential for the moisture in the ground to be pushed up into the walls as the floor isn't able to breathe. This makes me nervous.

I'm also worried that the houses either side may have put DPC in and/or rendered themselves,pushing any dampness onto our side, putting more strain on those walls. I am thinking that we do need to err on the side of caution.

The other half has had a quote for tanking the walls with 'optional' combiflex jointing system to wall/floor. It goes against my feelings as the damp will only be held in the wall long term but I'm not sure if I have any choice. It comes with a 10 year guarantee and that feels better to me than leaving people with a potential problem!

I'm not sure what I'm asking. I'm just seeking opinions from those that generally share my feelings about "damp". I guess we are in a basement, even if it doesn't exactly feel like it. We have always avoided basements in the past, we've been caught out!

BJV

We have a large office with a basement and we had to have it tanked. Tanking will or at least dose not have to mean leaving the water to stand. There are systems like the one we have which will periodically pump anything out and flush ???

I would not take any chances, damp and there are lots of different types is a horrible nasty thing that come back at any time. Speak to a specialist.

teneighty

In my experience the only way to achieve a damp proof basement is to use a cavity drain membrane.

I have seen too many of the waterproof renders and other cheap quick fixes fail.

Furts

I am uncertain. Are you saying there is a light well down to the basement with steps going down this? If so the basement wall does not retain the street? Or is it an old coal storage area where it does retain the street?

The ten year guarantee should be insurance backed, but it is possibly so full of exclusions to be almost worthless. Here one has to watch the installers like a hawk and pull them up on everything.

Doozergirl

No retaining walls around the house. The coal area is under the actual public pavement surface, so there is a substantial light well between pavement and house.

The only link to 'earth' is at the front where the party walls make it through a porch to the coal sheds, but still 2 metres away from underground.

We're being quoted full Sika tanking, insurance backed as an extra 10% cost. I will look at the cavity drain when I have not been to the pub. I do recognise it.

Thanks

Furts

I do not see the point of a cavity drain. You do not have a real basement, just external walls like countless other homes. Any damp here can only either be rising, or from rain on the external surface. The latter can be a problem, with the light wells not receiving good air flow and general ventilation. Equally if water drains into the well, be it off the street or off the building there is more damp.