Stopping damp in rubble stone wall resting on rock

[danieldodson]

I've got an issue with damp getting into a newly plastered wall. Previously the wall was blown at the bottom and there was a lot of pink plaster used. Now this rubble stone wall has been padded out with NHL 3.5 and then plastered with 30mm of Secil EcoCork and 6mm of fine hemp. Water is obviously getting into the wall from the outside where the rock is higher. The wall is still sound at the moment but obviously wet. You can see where the sawdust (from cutting the floorboards) is sticking to the wet wall.

I'm keen to explore external options for how to solve this. The property is located in North Wales and I've tried to contact the local Soverign chemicals rep for technical support but without any joy. They have a product called Weather Chek which the local builders' merchant can supply. Is this suitable? Other ideas I have are to put a channel outside and a bell bead above said channel near the foot of the wall to divert water away. Is this a sensible way to tackle the issue?

This is the outside aspect of that same wall. The wet patch of the interior wall runs roughly from the slate slab leaning against the wall down to the gas box. The sharp sand pile is no longer against the wall.

 

[George_engineer]

I suspect the render is cement based which will seriously slow down drying. Also, the external concrete hardstanding will bounce water back onto the wall and these are often laid on top of the previous ground - raising the external ground level (should be 150mm below internal ground level). How does the surface drain in rainfall?

I would consider removing the render and cutting back the external concrete. Chemical treatment is unlikely to help much.

 

[JohnD]

Water is obviously getting into the wall from the outside where the rock is higher.

Do you mean the external ground level is higher than the internal floor level?

The external concrete is clearly wet and mossy. Why?

Do you know why somebody thought it would be a good idea to apply a cement render to a stone building?

What was the building used for, before its conversion?

What is the floor made of?

 

[danieldodson]

I think the external concrete hardstanding was put there to get a constant slope for water to run off. Yes it does raise the ground level but without it water might not have such a clear path away down the hill. But I think a channel would be better. So yes, the external ground level is higher than the internal floor level. There is scant height in the room so raising the floor is not an option. Floor rests on battens, moisture barrrier and then slate chippings.

Cement renders on houses in the area are pretty common. My understanding is that the render was applied sometime in the 80s. Not sure if it was done on a grant or something like that. It has always been a house. Definitely no DPC in the walls. I would guess that it was built at the end of the 19th century. It was part of the Penrhyn estate as were most of the houses in the area.

 

[JohnD]

. So yes, the external ground level is higher than the internal floor level.

How much?

 

[danieldodson]

How much?

I have not measured it but I would guess probably external level is 150mm higher. Obviously it varies but roughly I believe that is what it is.

 

[JohnD]

I think you ought to lower the external level by at least that amount. Line the trench with cobbles or pebbles which do not hold water to enable it to drain. Lead the trench away from the building.

Adding an impermeable layer outside will not prevent water getting into the wall because it will enter from underneath

There is a chance you will find a layer of slate while you are digging. Remove all sources of water such as leaking drains, gutters and downpipes discharging onto nearby ground.

Exposing bare stone will allow some water to evaporate off the surface so the watermark will not be so high. I don't think you will ever make the wall dry. You can conceal the damp on the inside but ventilate it well.

Your wooden floor must be well ventilated to external air. You can use periscope vents. You might do better to dig it out and lay a new floor with DPM turned up the walls to isolate it from the damp walls. You can incorporate insulation.

Silicond injections will not help.

 

[tell80]

Your S&C render is in ground contact and capillary action is creeping up at the base of the wall.
You could cut a neat line of, say, 50mm away just to break ground contact?
How you would dig out a French drain is hard to say given, if I understand you right, you appear to have rock just below the surface?

The verge of the lean-to is leaking or was leaking.

 

[Koolpc]

As above, render touching ground. Not good.

Also, dig out and lay a french drain.

 

[danieldodson]

Your S&C render is in ground contact and capillary action is creeping up at the base of the wall.
You could cut a neat line of, say, 50mm away just to break ground contact?
How you would dig out a French drain is hard to say given, if I understand you right, you appear to have rock just below the surface?

The verge of the lean-to is leaking or was leaking.

Good point about the verge. I fillied in some missing mortar a year ago there but I don't know that I necessarily remedied the actual cause of the mortar having failed, perhaps there is a broken slate that I missed. Next time I'm there and it is raining I'll check.

Removing 50mm of render from the base of the wall sounds sensible and I will look at getting that done and report back.

Re the French drain, yes I think this is going to be hard (excuse the pun) to do and quite limited in how deep I can go. At another property nearby we dug out a french drain round the entire property about 1ft deep but that property wasn't directly built on rock. I don't think this would be possible here without cutting into the stone. I've no experience at how difficult cutting into the stone would be. None of the other walls have any significant problems with damp, it is just this larger gable wall (only one gable).

 

[Koolpc]

With the right tool, cutting into stone should be fine.

 

[tell80]

Not the best tools for a DIY'er to learn on but the best tool for rock cutting would be a large corded disc cutter - but given that the depth needed would be approx 300mm, the disc cutter would only go so deep - its then a case of jack hammering.

 

[tell80]

OP,
is the floor solid or suspended?
All affected damp wall plaster needs knocking off and rendering with a 4:1 mix of sand and lime.
All external render needs the same.

 

[danieldodson]

OP,
is the floor solid or suspended?
All affected damp wall plaster needs knocking off and rendering with a 4:1 mix of sand and lime.
All external render needs the same.

So the builder I was using only had this plastered 3 months ago and the internal plaster is sound. Is removing the plaster really necessary yet? I'd agree with you if it were gypsum plaster but surely since it is already lime based - and therefore breathable - it should not be necessary and not worth moving to a weaker lime sand ratio. Having already spent thousands on getting this done and a lot of hassle and time, I'm reluctant to tear up things that will further delay the works. It's a solid floor underneath, large stone slabs with a layer of slate chippings to level it off. I made a mistake earlier, it isn't a vapour barrier underneath but an impermeable layer of thin insulation - exactly the same that is protecting the floor on top in the photo. I'm honestly not worried about rising damp from the floor as I'm convinced that it is the water getting in at the base of the wall outside and that is the situation that I want to manage. There is so much rock underneath the house that there is probably very little earth from which water will come.

 

[Koolpc]

Excavate outside. Only long term solution.