Water-proofing basement

[mrcharly-YHT]

Step daughter has bought a house on a steep slope.

Downstairs, the room has exit door to garden at one side. The other wall is underground to the height of the ceiling and is damp.

They want to convert the room for use as a kitchen.

I'm not very up todate with waterproofing methods.

One proposal is to coat the walls with a waterproof slurry. Apparently this is called 'tanking' these days. Plaster on top.

The other is to affix a membrane, gap then dry lining.

My gut feeling is that a 2metre water column is going to apply a lot of pressure to the slurry, probably cracking it.

Input from experience and expertise, please.

[Little Jim]

Even modern basements built using waterproof concrete leak very slightly, so applying an internal membrane to the wall to "tank" it will not completely solve the problem, the water pressure will lift it off the wall.  Tanking is better applied to the rear face of the wall when it it built.  Better to use a drainage membrane - a sort of plastic sheet of egg boxes that comes on a roll applied to the internal face of the wall to collect the water and allow it to drain down to a drainage point and then build a second water tight skin inside that using a waterproof membrane to the rear of the inner skin.  This is, essentially, how all the modern basements, the essential must-have for people with too much money, are now constructed.

[mrcharly-YHT]

What about the floor? I presume that would need a membrane, sealed to the wall membrane? Or is it possible to just use waterproof slurry on the whole lot?

This room does have the advantage that the ground slopes down on the side. So one short side of the rectangular room opens onto ground level, one side is a party wall, one long wall has ground sloping from ceiling down to ground over the length of the wall. The other short side has ground to the ceiling.

[Little Jim]

Normally you would use the "egg box" (I think it is called waffle drain) under the floor screed, connected to the wall drainage and leading to a sump with a small pump in it.  You might not need to do it if the floor has a proper DPM in its construction.  If you wanted to go down this route it would be best to get an architect involved who has experience in this type of work then they can give you proper advice and specify the correct materials.

I assume that digging down outside and installing tanking and drainage along the buried walls is a non starter?  Tanking on the outside is much more effective as the water pressure cannot push it off.

[mrcharly-YHT]

Cost, location rule out tanking on the exterior.

I doubt the floor has a DPM.

Sounds like the project will be a great deal more expensive and complicated that they thought.

[Canardly]

Mastic asphalt could be a possiblility for the floor.

[mrcharly-YHT]

DAughter has a quote for the work.

Basically a builder is saying they will dig out down the side of the house, dpm the wall on the exterior and put a perforated drain pipe down side of house before backfilling.
Foul water drain manhole is at front of house (uphill side).

So I'm wondered where the perforated pipe would lead. Is it acceptable to just terminate in a soakaway in the garden?

[SoreTween]

DAughter has a quote for the work.

Basically a builder is saying they will dig out down the side of the house, dpm the wall on the exterior and put a perforated drain pipe down side of house before backfilling.
Foul water drain manhole is at front of house (uphill side).

So I'm wondered where the perforated pipe would lead. Is it acceptable to just terminate in a soakaway in the garden?

Yes. I was recently told current regs are 5m from the house.

[cygnet]

Tanking the outside is good. What have they proposed for the floor? (Water doesn't care where the gap in protection is)
Converting to a habitable space might need more/diverse protection.

[mrcharly-YHT]

Tanking the outside is good. What have they proposed for the floor? (Water doesn't care where the gap in protection is)
Converting to a habitable space might need more/diverse protection.

I was a bit worried about that - because there is nothing listed for the floor.

However, new info (to me) is that it seems foul water is seeping into the basement, suggesting the drains from the downpipes (which are at side of house) are leaking. No damp or sign of water on floor.

So the builder is going to excavate down side of house, make good piping, DPM side of house, put in said drainage to take water away (which is a step I think is the really important one).