Treatment of old brick wall below ground - bitumen?

[Zebra]

Dear all,
This summer I completed my French drain arrangement. The house is around 300 years old. Along one side the ground level is about 300mm higher on the outside than the inside, and I dug a trench right up against the wall of the house, since the land on the other side is the churchyard, so I cannot dig a trench further away. Neither can I leave it open because of the risk to the public. (The church are fine with what I've done.)
So it's a trench say 300mm wide and 450mm deep (to the depth of the foundations) with a drain pipe in the bottom, which drains away to a soakaway. The trench is lined with geotextile to prevent dirt entering it, and filled with coarse gravel. The geotextile is wrapped over the top, with a shallow layer of pea shingle on top of that. The brick behind is bare. (It's a 9 inch solid brick wall.)

Now I've had a architect do a specification for me for the woodfibre-based external wall insulation which I want to use. He's consulted with an expert in the application of external wall insulation to historic buildings, so I'm inclined to consider his suggestions seriously. He says that this wall needs to be protected from groundwater as much as possible, and thinks that the wall will not dry externally through the gravel, only internally. He therefore recommends applying a bitumen coating externally to the brick, then a drain membrane system followed by a 40mm layer of XPS (extruded polystyrene foam) insulation, then a Baumit render. This layer would continue from the bottom of the French drain to 300mm above the external ground level, where it would then join, with a drip bead, to the vapour-open woodfibre insulation system above.

There are a few words in there that ring alarm bells with me. Applying bitumen to the brick? Would anybody have any views on whether bitumen would damage old brickwork?

What do you all reckon about having a non-breathable coating on the walls to above ground level, then switching to the breathable system? He's not recommended non-breathable materials anywhere else in the building, but feels that where the wall is below ground, the risk of ingress of ground water is more significant that the drying afforded by the breathable finishes.

Any views?

Thanks

 

[Lime]

He says that this wall needs to be protected from groundwater as much as possible,

The problem with that assertion is that it assumes that water penetration/saturation is a one-way process, i.e. into the brick.
What actually happens to a buried permeable wall will very much depend on what happens to the soil/subsoil and ground water levels.
If you accept the premise that ground water must be stopped entering the wall, does the application of a bitumen coating actually achieve that?
If the ground water level is relatively high, what is to stop the water permeating up through the brick foundation?
i.e. water entry into parts of the wall in contact with the earth but not coated.

 

[middi]

Bitumen based masonary sealing products do not in themselves do any damage to brickwork.

They will ( as the word implies ) create a barrier to prevent water intering through the surface of a brick or other masonary construction to which the " paint" is applied.

These paints will not allow water which has gained entry from other directions ( ie- from ground capillary action) to be dispersed trough the painted surface. The only way water can be removed from the " saturated " substrate ( or bricks, as in your case ) is to evaporate through the same route that entry was gained.

All this waffling about entry or no entry of water or as to how it gets out is not the point as to how brickwork will suffer damage. The damage to " water saturated " brickwork is caused by FROST ( and to some extend ground salts). As bricks themselves come in so many different grades, the rate of moisture absorbancy is also different and so is the rate of degradation and failure when our mr FROST decides to pay them a visit.

Wet bricks don't really suffer much damage this is the reason why you have been advised to ( at least) stop water entry gaining entrance from the external face and insulate that area, If water gains entry from other directions it can go out the same way but the outer surface of the brick will be reasonably well protected from mr FROST due to the insulation factor.

It is not a good idea to apply sealing paint directly onto the face of bricks at ground level ( or exposed bricks below dpc), the capillary action will saturate the bricks and these will succombe to frost damage. These bricks are best left unprotected and exposed to the fresh air so they can "breath" . Unless you insulate the exterior of the brick of course.

Middi

 

[Keithj]

We have brick foundations going as far down as Tudor ones do (so not very far). They are in earth. When we had the repair works done, these vintage bricks were in fine fettle. Below ground there is little risk of frost, although I suspect a seriously cold winter might freeze the water in them.

Unless you are going to dig down underneath the bricks and seal them there, I could see water permeating back up inside the bricks from the unsealed bottoms. It then will have nowhere to go. Without the bitumen it would be able to escape outwards into the French drain.

Surely since your French drain is deep enough, it will carry the water away. Is it waterlogged or dry inside? If it's dry, then the bricks will be dry.

WIthout wishing to insult the architect, is he an expert in period properties? I've seen many examples of well-meaning experts who specified tanking or injected DPCs.

 

[Feltwell]

Neither can I leave it open because of the risk to the public.

How about leaving it open, but with a metal grid over the top?

 

[JoceAndChris]

There are a few words in there that ring alarm bells with me. Applying bitumen to the brick? Would anybody have any views on whether bitumen would damage old brickwork?

Would you like piccies of how bitumen has damaged the lovely old brick walls in my sunken kitchen? Also in this kitchen, there are different brick sunken walls, deep piled with earth on the outside, that are completely fine. They don't have any bitumen. I am talking about an interior tanking sysytem, now 25 years old, that we will have to pick off somehow. The moisture has pushed in and is pushing off the plaster, bitumen or not. Thr bricks crumble and fall down. It makes me want to cry every single day!

No bitumen will evr be allowed near my house again.

Well done on your drainage construction, Zebra.

 

[Zebra]

Thank you all. The way in which the architect was proposing to protect the bricks from water ingress from below, was by means of an injected dpc. (He says he very rarely recommends it, but that in some cases it is appropriate.)
I didn't mention that to you all in my first post, as I knew that would set everyone off :wink: and wanted to get your veiws just on the bitumen at first. I don't intend to have the injected dpc, needless to say!
So let's see, if the brickwork is insulated from the outside by means of the XPS as the architect proposes, then frost damage to the bricks wouldn't be a risk, it's just moisture we're considering. If I had the bitumen and the XPS without the injected dpc, then the moisture would have to travel further up the wall before being able to evaporate, i.e. to 300mm above ground level where the breathable layer starts. Or it could evaporate indoors (I will have lime hemp plaster).
Middi you say bitumen doesn't damage bricks but JoceandChris you say you wouldn't have it anywhere near, although you're talking about internally. It seems to me that it would do less damage than a cement waterproofing system, which takes the faces off the bricks when it's removed, but that it would mark the bricks forever, and that if it were to break down and crack over time, you'd have the problem of water getting in and not being able to get out (likewise if the proposed injected dpc ever failed, water would get in and not get out).
I like Lime's point that the issue depends on soil/subsoil and ground water levels. In actual fact, there isn't a high water table, I don't really have a rising damp issue in this area. Right now, it's bare brick indoors, bare brick and French drain outdoors, I've dug the cement slab up at the edges to let it breathe and the soil under the brickwork OK it's a bit moist but not sodden! The bricks feel dry to the touch.
I could leave the lower part of the wall as it is - bare brick in the French drain, and apply a lime hemp plaster indoors - but for the fact that I'm going to have this external wall insulation which starts at 300mm above external ground level - which is 600mm above internal ground level - and the lower part of the wall would have no insulation at all.
Would it work do you think to have the XPS to insulate that part of the wall externally, without either the bitumen or the injected dpc? Or better to let the brickwork breathe through the French drain if indeed it does, and not insulate there?

 

[Moo]

I don't know whether this will be of any help, but when we started work on our house twelve years ago the back wall was wringing wet. I guessed that it was because our back garden consisted of a concreted yard that sloped towards the house.
So we got rid of all the concrete, levelled the ground, and laid flags with wide, ungrouted, gaps in the hope that this would allow rainwater to soak into the soil rather than into the brickwork.
Our builder suggested that while we were doing this he should dig a trench along the back wall (with a lining that looked to me like very deep plastic guttering) that would take any rainwater into the main drainage pipe, and cover said trench with a metal (removable) grating.

It works a treat, even in the heaviest downpour, and the house has been bone dry ever since.

 

[Zebra]

a trench along the back wall (with a lining that looked to me like very deep plastic guttering) that would take any rainwater into the main drainage pipe, and cover said trench with a metal (removable) grating

That is interesting. How deep is it? Is it right up against the wall of the house? And is the wall left bare brick?

 

[Moo]

It's only a few inches deep (I'll brave the elements and measure it, if you really need to know), right up against the exposed bricks at the base of the wall.
On the inside of the wall the floor level (slabs laid straight onto soil) is only marginally higher than outside, and we have no damp at all there either.
And at the front of the house, in the cellar (where I am at the moment) there's a bare brick wall where only the top 18" is above pavement level; I've just given it a good 'feel' and there's no sign of damp there, either.

Which leads me to suspect that the walls can cope with the amount of moisture in the soil, but not the occasional monsoon - but, of course, that begs the question of the water table. We're quite a way above river level.

 

[Zebra]

I'm rather inclined as you say to let the wall cope with the damp by itself and not put any barriers in. The architect would seem to disagree with this, as does the technical expert from the company that supplies the breathable external wall insulation. Do you know, the process of working on this house is the strangest thing. Half the time I feel so out of my depth, like I have no idea what I'm doing and I wish someone would tell me what to do. So I pay an expert to work it out for me, and then I reject half of what they say because I think that (with all you people's help!) I know better myself!

 

[middi]

I'm rather inclined as you say to let the wall cope with the damp by itself and not put any barriers in. The architect would seem to disagree with this, as does the technical expert from the company that supplies the breathable external wall insulation. Do you know, the process of working on this house is the strangest thing. Half the time I feel so out of my depth, like I have no idea what I'm doing and I wish someone would tell me what to do. So I pay an expert to work it out for me, and then I reject half of what they say because I think that (with all you people's help!) I know better myself!

Take the advise of the " experts" which have viewed and assessed the situation- with written 25 year guaranty- and see what their reaction is.

Or ask them what needs to be done to guaranty the work for 25 years and note the comments.

If none of the above does not appear convincing, do nothing, and leave the brick faces exposed to fresh air. if, in time, this does not appear to be satisfactory , you have not lost much and can re-think again.

( just another way to look at it)

Middi

 

[Zebra]

do nothing, and leave the brick faces exposed to fresh air. if, in time, this does not appear to be satisfactory , you have not lost much and can re-think again

Well yes except that if I am going to do anything, I need to do it at the same time as doing the external wall insulation.
I can go against the advice of the architect and the technical experts but I think I need to have made up my mind!

Take the advise of the " experts" which have viewed and assessed the situation- with written 25 year guaranty- and see what their reaction is. Or ask them what needs to be done to guaranty the work for 25 years and note the comments

Sorry middi, I'm not sure I understand. You think go for the bitumen system if they'll guarantee it? Or are you being sarcastic about salespeople? (Sorry, difficult sometimes to detect irony in writing!)

 

[Moo]

A couple of options to consider:

Take the advice and have the bitumen and insulation done. If it doesn't solve the problem you've wasted your money.

Postpone taking the advice, just go with the trench + grating cover option, which will be cheaper, and wait a bit to see what happens. If it doesn't solve the problem you can think again about the bitumen etc.

Which is a long-winded way of saying 'take it one step at a time'.

 

[middi]

If I were in your situation ( and if am interpreting it correctly) I would not entertain sealing paints or dpc injection . Paints and dpc injection is totally useless in soft bricks I would leave the brickwork exposed and let natural ventilation deal with any damp problem.

If you managed to remove excess water from the perimeter of you house quite swiftly, and you are located on a reasonably well drained site, it should be ok. As you can appreciate what may work quite well in a certain situation may not work so well on another.

If you have had professional advice from specialists that have been on site, one would assume that they would have assessed the situation correctly. The only corcern I have is any conflict of interest these professionals may have in selling something.

We can only make suggestions as to what could be a course of action to take, consideration has to be given to the type of terrain, brickwork porousity, situation etc...

Unfortunately this can only be made by close and thorough inspection of the site.

Base wall damp is not a " cut and dry" ( excuse the pun) situation.

There is a guaranteed way of never experiencing damp again in these situations, usually the only obstacle is the cost and disruption involved, ie- installation of a dpc by cutting into the base wall and the dpc lapped into a dpm into the floor. ( a few thousands of pounds !!!)

I wish I could, categorically, advise on a quick remedy solution that it would " guarantee" no damp ever again.

Sometimes the simplest and quickest solution works perfectly well.

MIddi

 

[Flyfisher]

Do you know, the process of working on this house is the strangest thing. Half the time I feel so out of my depth, like I have no idea what I'm doing and I wish someone would tell me what to do. So I pay an expert to work it out for me, and then I reject half of what they say because I think that (with all you people's help!) I know better myself!

I certainly do know that feeling, and I'm sure many others on here do too. I generally subscribe to Moo's "one step at a time" suggestion to which I add "and give it time". This may be a result of inherent laziness on my part, but my feeling is that a lot can depend on how long a particular problem has already existed.

I imagine an old house being in equilibrium with its environment and if that environment has been pverflowing gutters/downpipes for 5 years, a leaking roof for 10 years or raised ground levels for 20 years, then it seems unreasonable to expect the house to suddenly find its new equilibrium when these problems are suddenly fixed - indeed, it may not even be always desirable. It takes a lot of time for damp walls to dry out and, frankly, I suspect it's better for the building to let it slowly find its new equilibrium than to 'force' it in some way.

I appreciate such things are sometimes easier said than done, but I think they're worth at least bearing in mind as we rush to apply all our new-fangled instant techno-fixes to buildings that would probably have been quite happy had they not been inadvertantly abused in some way.

 

[Keithj]

I'm old and cynical.

Experts selling stuff will assure you that what they are selling is the bees knees. That's how this house got its "injected damp course", which cost the poor unsuspecting then-owner some thousands of pounds for the high-tech stuff they used. It was a total waste of money.

When we had the proper repairs done, we picked out the little placcy sausages that had gone nowhere (other than to fill the holes drilled for the machine to inject the stuff).

Another set of experts had subsequently applied the wonder solution for damp/partly rotten sole plates: smother them with concrete. That resulted, 15 years later, in there being no sole plates and the house being suspended on the concrete (with some brown wood dust filling).

Our "real" technical adviser put it to me very simply: the house has been here since around 1500. Most of it is still sound: the bits that aren't are the ones where modern technology has been applied. The Tudor builders used brick, oak, and lime (mostly): so should you. So we did.

The only problem is that the green oak they had to use shrinks and cracks for the first few months/years/decades (don't yet know which) so we've got lots of gaps to pack with wool (in winter) and lime (in summer).
The old wood is fine.

 

[Zebra]

I'm totally in agreement Flyfisher, that the building needs time to recover, and I'm with you Keith about not having injected damp proof courses and cement render. I'm just trying to plan properly for the works which will take place next year, so that I can do the lime rendering in the summer. I could do nothing and leave it as it is, with the cracked cement render and no external wall insulation, but is that better? It's absolutely freezing in here!

 

[tobydog]

On a related topic (black paint on old bricks above ground level) I understand that you can buy plinth paint which takes about two days to fully cure but is actually breathable. Has anyone tried this? I would like to try and remove the existing black waterproof paint on our house but there's a fair chance the bricks are, or will be, damaged and therefore I'm looking for a healthy option to replace it.

 

[tobydog]

Here's the stuff:

http://www.enviro-live.com/plinth-paint.html