Can anyone advise on waterprrofing rock face in solum?

[aa44]

I am building a house (for me) which is on a rocky, sloping site. There is a solum behind the rooms downstairs at the front that rises steeply and then levels off. The face of the steep bit is a very uneven rock surface.

Has anybody got any suggestions about how I can treat this to seal it? One of the local contractors suggested just painting it with bitumen paint but I think that the surface has too many fissures in it for that. (Some of the cracks are probably 10 mm wide). My BCO is no help.

I have been reading up on two part concrete slurry products but they also seem to be too fine and thin. What I think I need is some sort of mortar cap that could then be coated with a waterproof slurry. Anybody got any suggestions?

 

[r896neo]

How you expect anyone to give you advice based on the few sentences you provided is beyond me?

With some photo's and detailed description people may be able to put some possible scenarios to you but really you need a professional on site to look at it. I assume you have a steep sloping site so drainage may be a major factor and you'd need to see the lie of the land around as well as ground conditions.

Sorry if that seems a bit harsh and its not building controls job to come up with engineering solutions. Pay an engineer.

 

[themiddleagedun]

Could you build a block wall in front off the rock and apply your waterproofing to that?

 

[OwainDIYer]

if you waterproof the rock face you will end up with hydrostatic pressure behind the rock face, which can cause Very Bad Things to happen.

I'd suggest contacting a structural engineer or groundworks contractor.

 

[^woody^]

How you expect anyone to give you advice based on the few sentences you provided is beyond me?

There is more than enough information there from the OP .... a rock surface with some fissures which the OP wants to coat to seal it. What more do you need, a geological survey?

Assuming the rock is stable, then yes you can use a cement slurry or even a slurry with some fine grain washed sand to thicken it a bit for the wider cracks and crevices. And then coat with a suitable compound - of which bitumen may well do ... but not bitumen without a further non-reactive coating if this area is going to be used in any way

The rock would presumably be non-porous, but if there is a chance of moisture under any slight pressure then you would need a coating product to deal with that rather than standard bitumen

 

[Norcon]

Had to look "solum" up.
Just stick a big concrete retaining wall in front of it excavating back whatever is necessary. Job done.

 

[aa44]

Thanks for the replies.

The site doesn't slope that steeply. The rock face in the solum is steep because it sits behind what the amercicans would call a walk out basement. It's not going to be an area that is used at all.

I am hoping that there shouldn't be much water trying to come out through the rock because there will be a perforated drain all round the house, including either side of the solum. The rock is stable, i.e. it's not going to move but it is a mica schist which is quite shale-like and so has lots of fractures in it. It's not impossible that water might work it's way through from somewhere else on the site to a crack in the rock face.

There will be a perforated drain in chippings at the bottom of the slope so that anything that does come through can be led away and the back wall of the rooms in front of the slope will be tanked. The house is ICF and the bottom metre of the walls is poured concrete with a waterproofing admix so the only weak spot is the join between the concrete wall and the foundation.

Anyway thanks for the replies.

 

[r896neo]

There is more than enough information there from the OP .... a rock surface with some fissures which the OP wants to coat to seal it. What more do you need, a geological survey?

On a sloping site a solum could be 5 foot high and need an engineered retaining wall. Creating a dam by waterproofing it might be a terrible idea and need a proper engineered solution rather than yea go ahead stick a bit of paint on it. So i was being a little careful. Obviously too cautious for woody's liking....

 

[aa44]

Here's a picture. As a belt and braces approach, the wall at the back of the basement has been designed with the strength to retain whatever is thrown at it. It's eight inches of reinforced concrete. In fact, the ground behind the wall won't touch it as the rock face is stable and is about 500mm from the wall at the bottom of the slope.

The bottom metre of the wall has a waterproofing admix in the concrete and the back face of the wall will be tanked. The drain will take away whatever water does get down there. I just want to stick something on top of the rock to try and minimise the chance that any water gets in there at all.

Untitled

• aa44
• 13 May 2012
• 1

The foundations are poured and the concrete wall is in place.

 

[OwainDIYer]

I think I'd be inclined to use some form of permeable geotextile, to stop any loose materials from the rock face blocking the drain, and allow any water to drain away easily rather than having it build up somewhere.

 

[aa44]

Thanks for that. It was a quick sketch to show the shapes so I didn't put all the details in but the drain will be wrapped in a geotextile.

 

[joe-90]

I'd love to see a piccie of the house. Any chance?