Damp again

[zunetunes]

I've long subscribed to the scepticism of rising damp and its prevalence and read quite a lot of articles, forum threads about the subject.
However ... my problem.
Victorian house. Wet part of the country. No dpc. Mainly sandstone rubble fill construction with some brick walls. Concrete rendered (I'm 99.9% sure the render is original). Interior of walls originally lime plastered but now a mix of lime, pink stuff and plasterboard. We have left some walls as bare stone after removing internal plaster/lime - a bit dusty but looks nice and means these walls dry out nicely if they are damp.
Been here 10 years and have gradually eliminated penetrating damp (gutters/rooves etc). In our hallway we definitely have damp that appears to be rising. It is on the side of the house that is near to the road where the ground is higher. Although most of the house is sandstone, one side of the hallway is brick. (I think it is a Victorian extension to the original building.This is one of the damp walls. I thought we'd cured the damp, had someone do a quick plasterboard job, but the new plaster shows damp up to 1 metre. the hallway does always smell damp.
So I'd be inclined to believe this is rising damp. Just to note the house is very well ventilated (ie very draughty). I could dig a ditch along the outside of this wall (currently paved with old stone) but due to the topography there is nowhere that water could drain to from this ditch. I have read on here that part of the problem could be water bouncing up from the paved area alongside the wall. i'm inclined to believe this could be a factor but not sure how I could deal with it.

So I'm thinking of trying the dreaded chemical injection along the brick wall as a trial. DIY should not be too costly. I understand that it should be injected along the mortar bed. Howevr I can't tell where that is due to the very strong concrete render. Should I just inject through the render and disregard whether it is into the mortar bed or hack off the render at low level (heavy duty job as it's really tough stuff this Victorian concrete)

 

[zunetunes]

So having posted that and reflecting more I guess there may be some room for doing something with the "paved" area. I could remove the stones and dig down by say a foot. That would reveal the bricks below ground level. Might that help? The problem I envisage is that when we have one of our torrential downpours the ditch would fill up with water

 

[malcolm]

Damp doesn't rise up plaster if you have a little gap between the plaster and the floor. Skirting boards were invented to cover the gap. Doesn't sort the problem fair enough but if you have a wet floor it stops the damp from going up the wall. A trench outside is an excellent idea if outside ground levels are higher than inside. You drain the trench into a soakaway.

Don't do the stupid modern chemical injection stuff - it is a waste of time. Better work out the problem and fix it.

 

[MikeG]

I've long subscribed to the scepticism of rising damp........

You shouldn't. It exists.

You should, however, be very sceptical of injected damp courses. In one sense of the phrase, they don't really exist.

 

[zunetunes]

Damp doesn't rise up plaster if you have a little gap between the plaster and the floor. Skirting boards were invented to cover the gap. Doesn't sort the problem fair enough but if you have a wet floor it stops the damp from going up the wall. A trench outside is an excellent idea if outside ground levels are higher than inside. You drain the trench into a soakaway.

The damp isn't rising up the plaster. It's rising up the wall and then through to the plaster above ground level.

Problem with a trench is there is no possibility of soakaway. At one end of the trench would be an old barn abutting the house and at the other end the road which is at a higher level.

IF I did a trench how deep would it have to be?

My only thought at this stage is a trench with a cover over it that doesn't touch the wall and causes rain to run away (not sure if even this is viable

 

[kreyszig]

Can you run the trench/french drain around in front of the barn, giving you better access to somewhere you can put a pipe into a soakaway?

 

[noj]

Whatever else you do, you really need to try to get the external ground level below that of the internal floor. 150mm below if possible. That may solve everything - but you'd need to wait for a number of months to see the effect.

Depending on the permeability of your soil and the general slope of the concrete hardstanding your trench idea could work without the need for a french drain (or it could turn into a moat!) - may be worth removing just a couple of the paving stones and digging a test pit to see what happens for a while? If it doesn't fill with water then extending it along the wall may suffice

And if it does fill up then you know that's almost certainly your source of damp and a drainage solution is really required!

 

[Spoilt Victorian Child]

How old is the concrete floor in the hallway? I'm guessing it wasn't put down at the same time the Victorian brick wall was built? I think it could be the culprit for what you describe as 'rising damp'.

BTW is your stone wall (with less high moisture line) still lime plastered by any chance?

I also wouldn't bother injecting chemical DPC. You need to find the actual cause and solve that. Drilling holes will just wreck your bricks/stones.

 

[MatthewC]

In our hallway we definitely have damp that appears to be rising. It is on the side of the house that is near to the road where the ground is higher. Although most of the house is sandstone, one side of the hallway is brick.

Do you mean that the ground outside is higher than the floor of the hallway? You need to get it lower by 6" or so, so remove your paving beside the wall and dig down, just 8"-10" wide should do it, which you can either leave open or find some grating to cover. Then let it dry out for 6-12 months before you even think of spending money on anything else.

 

[zunetunes]

Whatever else you do, you really need to try to get the external ground level below that of the internal floor. 150mm below if possible. That may solve everything - but you'd need to wait for a number of months to see the effect.

The level of the outside is currently 230mm below the floor level.

MatthewC - The road level is higher than the level of the ground immediately outside the house ( so no way of draining off in that direction) but the ground level outside is lower than the floor level

 

[zunetunes]

How old is the concrete floor in the hallway? I'm guessing it wasn't put down at the same time the Victorian brick wall was built? I think it could be the culprit for what you describe as 'rising damp'.

BTW is your stone wall (with less high moisture line) still lime plastered by any chance?

I think most of the concrete floor is same age as that part of the house ie late Victorian or just after. The hallway leads to stairs which seem to rest on the concrete.
The bit of hall nearest the front door (some slabs late on concrete) is of more recent vintage and I suspect may have a damp proof membrane.

The stone wall is modern plaster on the hall side and lime on the other room side

 

[MatthewC]

The road level is higher than the level of the ground immediately outside the house ( so no way of draining off in that direction) but the ground level outside is lower than the floor level

I trust that you don't get run off from the road in your direction?

I would start by removing the paving slabs as I said above. The splashback can affect the wall to a surprising height, regardless of its height in relation to the floor inside.

 

[Spoilt Victorian Child]

Hey Zunetunes,

Here's something that was happening in one of my floors, and what I'm guessing could be happening in your case, where you say the new concrete is. You would only know by excavating a little bit though. :-/

The floor had been dug out, and a plastic sheet had been placed over the natural sand/ash floor to protect the new concrete from getting damp and failing. But the sheet wasn't tucked into the wall in any way (ideally it'd be beneath whatever original DPC the wall had if any, sometimes slate, sometimes blue engineering bricks, I think).

The knock-on effect in my case was the moisture found it's way around the plastic sheet, and up the walls via the modern gypsum plaster someone had re-plastered with. If it had been lime plaster it might've stood a chance of letting the moisture escape, but the gypsum just soaked it up and caused a constant damp smell and stains up the wall, with paint/wallpaper failing year after year in those areas.

We dug the concrete and plastic out, it dried out in a matter of weeks, and the smell went.

Does the 'damp' in your walls correllates to the position of the 'new' concrete?

 

[88v8]

Here's something that was happening in one of my floors, and what I'm guessing could be happening in your case, where you say the new concrete is.

Exactly the situation we had.
Concrete floor with dpc.
Very damp at the perimeter.
Dug it out, replaced with limecrete.
Sounds easy if you say it quickly.

With your external ground being 9" below floor level, no problem there other than potential splash as Matthew said, so digging a trench isn't going to help.
Replacing the paving with gravel would be an easy first step. Gravel doesn't create splash.

If it were me, next step if that doesn't fix it by next summer, would probably be limecrete with a suitable breathable topping.
After that, a dpc properly sawn into the brick wall. But that gets expensive.

Ivor

 

[Flyfisher]

Replacing the paving with gravel would be an easy first step. Gravel doesn't create splash.

I wouldn't bet on it. We have a gravel bed against our house and a dripping gutter joint caused significant splashing against the wall. I was surprised on a number of counts; the gutter joint wasn't leaking badly, the gutter itself overhangs the wall by about two feet (as can be seen by the dry strip against the house after some recent rain) and I also thought that gravel would prevent splashing. Seems it only reduces it!

 

[zunetunes]

Have pulled up some of the "paving" - will post pics tomorrow.
Why is splash a problem? - the wall gets wet from the rain anyway

 

[frogman]

Here's something that was happening in one of my floors, and what I'm guessing could be happening in your case, where you say the new concrete is.

Exactly the situation we had.
Concrete floor with dpc.
Very damp at the perimeter.
Dug it out, replaced with limecrete.
Sounds easy if you say it quickly.

With your external ground being 9" below floor level, no problem there other than potential splash as Matthew said, so digging a trench isn't going to help.
Replacing the paving with gravel would be an easy first step. Gravel doesn't create splash.

If it were me, next step if that doesn't fix it by next summer, would probably be limecrete with a suitable breathable topping.
After that, a dpc properly sawn into the brick wall. But that gets expensive.

Ivor

How much was your limecrete floor? This plan b for me if my gully doesnt work. I was also thinking of maybe just a meter wide buffer zone along the one damp wall as a limecrete light option.

 

[88v8]

The room is about 12' x 15'.
4" LECA, 4" limecrete.
Would have made it thicker but there was insufficient footing and I wasn't going to get into underpinning.
Around £4,000 iirc, to break out the concrete, and install the slab, but best to get your own quotes as our specialist had a 120 mile round trip. And our cottage has access problems which made the job more difficult.

Ivor

 

[zunetunes]

So here I've excavated down by about 10". The render went below the outside ground level. The wall is brick above ground but below ground seems to be a mix of brick and stone. The inside floor level is about 1" below the level of the clip on the pipe