Waterproofing house from flower bed (Do I need a membrane?)

[GilesMDavis]

Right,

I was clearing some blown render from the outside of the house (old stone-built) and that got me thinking about the damp wall.

We have a flower bed against the wall, no idea how long it's been there - we've only lived here 18 months. As far as I can see there's no barrier between the soil and the wall.

I can't help thinking that a pile of damp soil against an external wall won;t be helping the damp inside.

Would it be worth digging out the soil and putting something between the bed and the house to keep it "dry"?

What exactly would I need? (I am a total novice at this sort of thing, so speak slowly!) Looking at some posts about damp garages there was talk of impermeable membranes and that got me thinking.

Thanks for any advice

Giles

 

[RedHerring2]

I'd go for an air gap if it's possible. So much easier to maintain/inspect.

You're going to be excavating it anyway, so why not excavate a bit more and install a barrier to retain the soil away from the wall.

Don't forget to aim for external ground level adjacent to the wall at least 150mm below dpc (if there is one).

 

[GilesMDavis]

I'd go for an air gap if it's possible. So much easier to maintain/inspect.

You're going to be excavating it anyway, so why not excavate a bit more and install a barrier to retain the soil away from the wall.

Don't forget to aim for external ground level adjacent to the wall at least 150mm below dpc (if there is one).

Thanks for the advice.

I think there isn't a DPC in this bit of the house - it's rather ancient - 3ft thick stone walls. Hence it's prone to mildew inside.

The bed's not huge - about 2m along the wall by 60cm out. There's then a concrete path. Could I add an air gap by putting something against the wall that doubles as barrier and air gap - bricks or blocks of some sort (or gravel?)

Sorry for noddy questions, I am a total beginner.

 

[RedHerring2]

I'm not an expert on this (or anything else tbh) I'm only a DIYer, so if any other posters suggest anything else, you might want to consider their advice also...but..
I would go with an air gap completely, no solids of any sort.
This could be achieved quite simply, depending on height of soil. Supposing the soil is only 200mm high or so, a gravel board retainer fixed away from the wall by about 100mm.

It is possible that engineering bricks placed against the wall may be OK, but a) you're still going to get soil permeating the joints unless they're mortared, in which case build it away from the wall anyway. b) there's no airflow to the wall so any dampness can't dry out.

It sounds like you could lose the soil bed completely.

How high is the soil?

 

[GilesMDavis]

That sounds like a top idea - I'd never heard of a gravel board before.

I have no idea how deep the beds are but I suspect they are not huge. They support a wisteria (lovely but grows like mad) and a few tulips (much less hassle!).

I might dig down to see the depth then I could slide in in a couple of paving slabs to act as a gravel board. Not quite sure how I'd keep them upright but I'll have a think.

Brilliant advice! Thanks

 

[RedHerring2]

Just think about reducing the height of the beds to about 150mm below what would have been a dpc, which would have been about 200mm below the internal floor level.

If that's too much then you need to think about the 'retaining the soil away from the wall' idea.

If you use something like 900mm X 600mm slabs, placed upright with at least 300mm buried in the ground and about 100mm away from the wall, I think they should be OK.

If using gravel boards, think about burying them up to about half way.

I wouldn't want to retain any more than about 300mm to 450mm of soil using this method.

Bearing in mind my comments about me not being an expert and if any regulars provide conflicting/ more experienced advice, please consider it.

The reason for going 150mm below where the dpc would have been is to prevent rain splashes splashing up the wall to a point above where the dpc would have been. Another way to avoid that if you can't reduce the soil low enough, is to provide some sort of barrier to deflect the water away from the wall. Or you could think about providing some sort of surface to minimse rain splashes, like a decent layer of pea gravel.

 

[GilesMDavis]

That's genius. I'm also looking into adding some external waterproofing to the paintwork. Should be nice and dry once we're done.

Thanks again for the ideas.

 

[RedHerring2]

Hmm, sorry to pipe up again, but I'd give serious consideration to your idea of waterproofing the wall.

Going on your description of the situation so far, I'm guessing:
Thick stone walls, lime mortar, no dpc....the walls are meant to breathe.

That is they will take up some moisture but they will 'expire' that moisture again. Obviously a covering of soil has prevented that previously.
If you apply a 'waterproofing' layer to the wall, you're going to trap the moisture in the wall and preventing it from drying out.

The only option for adding any layer to the wall is a lime render and my experience of that is extremely limited.
If you need any more advice on that I suggest you post a specific enquiry in the more appropriate forum: Plastering & Rendering or Building.

 

[GilesMDavis]

Interestingly I'm already posted up there ( //www.diynot.com/forums/viewtopic.php?t=246370 ) and that was a suggestion from earlier today.

The friendly builder never mentioned it, so I might just follow his advice.

I think a previous owner moved away from lime render, too expensive/high maintenance. I'm doing a patch-up; in the fullness of time and money we'll take it all back and re-do it properly

 

[JohnD]

if you put a barrier against the wall, it will do nothing but good. One method is to put a trench full of pebbles against the wall, with a barrier on the garden side. This will take the soil pressure without breaking, and transmit it to the wall. Pebbles also do not carry much damp as they have hardly any capillarity. This is called a french drain. Water may accumulate at the bottom, so lead it away from the house and downwards.

Excessive water against the wall will tend to wash away mortar between the bricks or stones, especially if it is soft lime. If you are exposing it, you might like to clean out and replace damaged mortar.

Interestingly, even if you waterproof the old wall all the way down to the foundation, it will not stop damp, as water will penetrate up from underneath. However, if you have a well-ventilated cellar or subflooe space, and the inside surface of the wall is exposed, some water will evaporate off the inside of the wall, so the higher you go the drier it will be.

 

[RedHerring2]

Edit: Sorry John, I was aiming my comments at Giles, not at you.

Fair do's. I've just read your other post. The contibutors in that post aren't fully aware of the situation, i.e. thick stone walls, no dpc, and I bet lime mortar.

Plus your interior problems of mildew, etc ,may be symptomatic of trapping moisture in your walls with a cementitious render.

I'd do two things: firstly make the other contributors aware of the full situation, see if they stick by their previous advice. Secondly, research the situation more. There's a heritage building web site that's very helpful. The link has been posted on these forums before, not by me. If I find it I'll post it.
In the meantime research lime render and lime plaster.

 

[GilesMDavis]

I like the sound of the French drain, John, I think that's even within my capabilities. I could also use some pea gravel on top and it might even look ok - which is not par for the course for me!

RH2, thanks for the clarification on the render - it's like learning a new language (yes, I even had to look up DPC the other night, d'oh).

I'm pretty sure it's not lime at the moment (the friendly builder had a look at it and all the houses round here are the same, so he's something of an expert!) but will research it out of interest.

I think the render is part of the mildew problem. Also I hadn't figured out the ventilation (i.e. trickle vents) until recently, it's already improved.

Cheers

 

[johnheritage]

If you don't want to use a plastic, you can push slates down the backs of the beds to encourage the water down and away from wicking up the walls.

I have no idea how applicable this is to old thick walled houses with no DPC, but does anyone have any idea if he could use an injectable DPC with this?

You can now buy them as cartridges to go in caulking guns. You drill holes every half foot or so (need to check the instructions) and then squeeze the caulk into the hole. It will permeate through normal mortars and create the layer. I could actually see mine going over a day or two when I used it, the mortar line looks greasy and the patches spread out until they touch.

It has the consistency of moisturizer when it comes out the cartridge and, again, feels greasy between your fingers.

If you can work a drill and tape measure, it's not all that hard to do.

 

[RedHerring2]

From my very limited experience, the stone walls tend to be constructed of two skins of stone with rubble in fill.

Because the walls are 900mm thick, there's no way that you can get the treatment to meet in the middle. So all you're doing is treating the outside 150mm, perhaps of both skins, if you treat both skins. The midlle 600mm of the wall will still have no dpc.

 

[johnheritage]

Yep, you're right.

With them being that thick, it'd need a small fortunes worth and deep holes. Maybe you could see if you can buy a BIG tank of it and rent an injector from someone, the cartridges likely have a premium on them given that not many people do them.

Another possible option if you're considering plastics would be to use a waterproofing paint behind the flowerbeds to get a complete seal.

You can also use 'tanking' if damp is a problem inside something like a basement. If you check out toolstation.com they have 5l containers of SBR Bond in the structural section, alongside the other admixes. It's chemical name is 1,3 Butadiene and it's a kind of rubber.

It's used for rendering and things like that as a backing layer on poor walls (more expensive version of PVA but chemically superior), to bond the render and prevent damp / salt problems. I'm sure it says on the back of the container I have that it can be used for tanking as well.

To tank a room, you paint the solution over every inch of the walls and floor and the SBR forms a waterproof liner. It stinks of new carpets, even more so than a new carpet, so it'll smell nice and new in there alright!

You could do every room in the house to get the damp out of the whole place, but again, with this being such an old house and built in a none standard way with regards to the SBR, you need to have a google and see if anyone else in such a building has used that before and if it's okay with regards to the breathing effect of the walls.

These places have all kinds of quirks, like the lime render requirement and so on. But I expect at least one other person will have looked into this and tanking.