Existing Damp Proof Course – Benefits or Problems

[J_Ashley]

We bought an end of terrace Victorian property last year and have gradually been doing renovations. Most of the work does not actually relate to issues caused by the age of the house, but rather remedying unsuitable/low quality repairs by previous owners.

We have managed to obtain documents relating to a chemical damp proof course treatment carried out almost twenty years ago. The damp proof course has been installed on all walls with an exterior face (given it’s an end of terrace this is all but the partition wall), to a height of around 60-100cm. Inside the property, to above where the chemical damp proof course has been inserted, there is then a very hard dark grey render acting as the initial layer of plaster. This looks rather cement like to me, and the documentation refers to ‘drywall chemical plastering’ that contains ‘drywall salt retardant additive’.

The property has no current dampness (all moisture readings have come back fine) and there does not appear to have been excessive damp problems at any time. The underfloor area around the bay window seems to have suffered slightly at some point in the past (presumably before this damp course was added), but quite why such an extensive damp proof coursing was added seems a slight mystery.

We have been trying to maintain/improve the breathability of the building using lime plaster and clay paints, and so the presence of chemicals/possible cements that restrict breathability makes me nervous. My questions are:
- Does this sound like an appropriate and well-executed treatment that is providing benefit?
- Is it likely to present a concern/problem for the future?
- Or is this a case of if it isn’t broken don’t fix it (i.e. everything is dry so leave well alone).

 

[plasticpigeon]

It isn't a mystery why there was a chemical damp proof course and cement render put on your walls. It was to make money, almost certainly fraudulently. Your house never needed it but this is an ubiquitous scam on a national industrial scale that mortagage lenders, surveyors and estate agents are either party to, or have no interest in stopping.The only people that benefit are the cowboys from the so called damp proofing companies. The amount of wasted materials and work not to mention homeowners money is absolutely criminal. However if your house doesn't seem to be suffering from these moronic modifications, forgot that they are there and live a happy life. However your lime plaster and clay paint is a bit pointless given the works that have been done in the past, you may as well take the easy option and use pink plaster and normal paint. Lime pointing outside is still a good idea though.

 

[Feltwell]

If it ain't broke, don't fix it would be my advice.

Yes, it was unnecessary and it is a concern of course because that waterproof internal render *can* hide damp in the wall itself. But, if it was done 20 years ago and there are no signs of any resulting problems such as ground floor joist ends rotting or damp appearing above the render line, then I'd leave it alone.

Use of cement or gypsum plaster in an old building *can* cause problems, but not always.

 

[CliffordPope]

I'm unclear whether the antagonism towards chemical damp-proofing is because they don't work, or because they do and a damp course per se is bad in an old building?

Surely a traditional slate or black firebrick damp course would be a "good thing" ? If a chemical treatment does the same thing, what actually is the difference?

 

[Kearn]

I'm unclear whether the antagonism towards chemical damp-proofing is because they don't work, or because they do and a damp course per se is bad in an old building?

Surely a traditional slate or black firebrick damp course would be a "good thing" ? If a chemical treatment does the same thing, what actually is the difference?

To make a broad brush statement, it's because what's often the case is that it is NOT a DPC in the functional sense. Therefore they don't work. And in fact cause irreversible damage to the ancient fabric. And merely mask an issue.

If it was a true complete barrier across the entire contact footprint of the ground floor and the ground below, serving it's purpose, then I don't think any of us would have an issue. Likewise for Victorian properties with slate courses originally built in. A DPC isn't necessarily a bad thing for an old house, if it is entire and provides a complete moisture barrier. However, retrofitting one properly is clearly a mammoth task to do properly. That said, solid wall construction will still enable some moisture ingress internally from the elements, even if the ground contact is dry.

However, this is usually not the case when it's referred to here. The cowboys injecting bricks to 'create a DPC' may as well be pumping snake oil into them. It only serves to leave ugly holes in old brickwork. And tanking / chemical painting doesn't solve an issue, it just hides the symptoms and/or moves them elsewhere as mositure can still move from the ground into the building and needs to exit somewhere.

 

[Flyfisher]

My questions are:
- Does this sound like an appropriate and well-executed treatment that is providing benefit?
- Is it likely to present a concern/problem for the future?
- Or is this a case of if it isn’t broken don’t fix it (i.e. everything is dry so leave well alone).

1. No
2. Maybe, maybe not.
3. Yes

Lots of information and disussion about this perennial subject online - here are a few results from a few minutes searching . . .
https://www.architectsjournal.co.uk/home/-rising-damp-is-a-myth-says-former-rics-chief/5204095.article
https://blog.completepreservation.co.uk/2015/01/07/rising-damp-is-a-myth-you-may-think-so-if-you-read-the-book-now-read-this-and-decide/
https://www.homebuilding.co.uk/damp-treatments-damage-home/
https://www.heritage-house.org/damp-and-condensation/the-damp-con-collection/injection-damp-proofing.html
http://buildingdefectanalysis.co.uk/damp/diagnosing-rising-damp/

Interesting video with Jeff Howells and Stephen Boniface discussing 'rising damp':
https://www.thenbs.com/knowledge/rising-damp

 

[J_Ashley]

Many thanks for the advice and links - I'll be sure to read through them.

Sounds like the DPC will be another “try to forget about it and move on with life”. Fortunately we don’t seem to be experiencing any damp problems, but it’s the uncertainty over potential future issues that remain a discomfort - I guess that’s all part and parcel of period property ownership though. We don’t want to go to the expense/hassle of renovation to then have to redo things in the not too distant future because we ignored them now. Equally though, undoing some of this stuff would be highly damaging itself and very expensive, and, in reality, there is no obvious problem to solve – only peace of mind about the workmanship.

Unfortunately the repointing was also done in cement. It’s hard to know the date, and it could have been done around the same time as the DPC, but is probably earlier (25+ years). We sought some advice and, again fortunately, it doesn’t seem to be doing much damage. We were advised that removing it now would likely be more damaging than the minimal detrimental affect the cement repointing is currently having. Leaving it to naturally weaken over the years to make removal easier, and then repointing with lime seems to be the way to go.

It frustrates me that it takes ignorance by two parties - both the owners and the workmen - to commit these mistakes! Such unawareness seems even more surprising considering that (thankfully) a lot of the original features (sash windows, cast iron guttering etc.) were never replaced with modern plastic versions.

 

[88v8]

Interesting.

But, the no rising damp theory, does not survive exposure to the Hobnob/coffee test.
And if there is no rising damp, why do houses have dpcs?

As regards the OP's query, I agree, not great but I'd leave it alone.

Ivor

 

[Gareth Hughes]

Interesting.

But, the no rising damp theory, does not survive exposure to the Hobnob/coffee test.
And if there is no rising damp, why do houses have dpcs?

As regards the OP's query, I agree, not great but I'd leave it alone.

Ivor

We don't build houses out of hob nobs, nor do we stand them in hot coffee.
If rising damp exists, why are dpcs not used in other countries (the Netherlands for instance where most buildings are permanently sitting in water)?

 

[MikeG]

Rising damp exists. DPCs and DPMs are just one way of handling the issue.

Anyone who claims that rising damp doesn't exist is going to need to explain to me how a house which I built, and which I then lived next door to for 17 years, had dark damp bricks below the DPC on the plinth, and light dry bricks above (same bricks of course).....every winter, and not during the summer. The name of the village ended in "...marsh". It's a lovely little theory, and there are some really weak bits of research backing it up, when the reality is that I can walk people around this area, with a moisture meter in their hand if they want, and physically show them the phenomena in action.

 

[Gareth Hughes]

Rising damp exists. DPCs and DPMs are just one way of handling the issue.

Anyone who claims that rising damp doesn't exist is going to need to explain to me how a house which I built, and which I then lived next door to for 17 years, had dark damp bricks below the DPC on the plinth, and light dry bricks above (same bricks of course).....every winter, and not during the summer. The name of the village ended in "...marsh". It's a lovely little theory, and there are some really weak bits of research backing it up, when the reality is that I can walk people around this area, with a moisture meter in their hand if they want, and physically show them the phenomena in action.

I take it that by "moisture meter" you mean a device which does not measure the moisture content of a wall and which will give completely misleading results in most circumstances?

 

[plasticpigeon]

Rising damp exists. DPCs and DPMs are just one way of handling the issue.

Anyone who claims that rising damp doesn't exist is going to need to explain to me how a house which I built, and which I then lived next door to for 17 years, had dark damp bricks below the DPC on the plinth, and light dry bricks above (same bricks of course).....every winter, and not during the summer. The name of the village ended in "...marsh". It's a lovely little theory, and there are some really weak bits of research backing it up, when the reality is that I can walk people around this area, with a moisture meter in their hand if they want, and physically show them the phenomena in action.

How high was the floor level inside the house? How high do you think the water would rise up the wall without the dpc? Obviously capillary action is a real physical phenomena but it is dependent on fluid and materials. I think all this is moot though, as I don't believe drilling holes in masonry, injecting something (silicone?), and cement rendering internally, which by definition wouldn't be needed if the chemical injection worked, is anything but destructive and fraudulent. It's looks like a cynical panacea preying on fear an ignorance to me.

 

[Flyfisher]

I once read that the issue with injected DPCs is not so much that they can’t work, more that they don’t work because of poor workmanship. The gist of the argument was that installers typically do not use enough time or pressure for the silicone treatment to fully percolate throughout the bricks and mortar. After all, imagine replacing an entire course of bricks with truly impervious treated bricks and mortar, wouldn’t that be exactly equivalent to a plastic DPC? So perhaps the theory is sound but the implementation is usually deficient? Unfortunately, I cannot find where I read that and really wish I’d kept the link.

What does surprise me though is that the seemingly simple proposition of ‘rising damp’ still seems to attract supporters and detractors is equal measure. I’m surprised there has not been some properly rigorous scientific investigation to answer the question one way or another.

 

[MatthewC]

My questions are:
- Does this sound like an appropriate and well-executed treatment that is providing benefit?
- Is it likely to present a concern/problem for the future?
- Or is this a case of if it isn’t broken don’t fix it (i.e. everything is dry so leave well alone).

1. No
2. Maybe, maybe not.
3. Yes

+1

If it ain't broke, don't fix it would be my advice.

+1 again

I'm unclear whether the antagonism towards chemical damp-proofing is because they don't work, or because they do and a damp course per se is bad in an old building?

Surely a traditional slate or black firebrick damp course would be a "good thing" ? If a chemical treatment does the same thing, what actually is the difference?

At best a chemical DPC is a waste of money and at worst it can cause huge irreversible damage to such a building, as the chemicals used can have a very bad reaction with limestone; it isn't doing the same thing as an inert slate DPC.

As for whether "rising damp exists", I certainly believe in capilliary action. The question is how high can it go? Water has a certain value of surface tension, and this is what makes it rise up but diameter of the holes in the stone/brick/mortar governs how far up. This of course depends very much on the exact material used.

Who's been to Venice? The fact that the place still stands is surely testament to the fact that capilliary action can only lift water so far. In fact in some places the walls are eroding away but it is the water traffic which causes the base of the walls to be wet up to a few feet and thus causes the erosion.

The approach of DPC salesmen in general is simply to pretend to be "experts" when in fact they are just salesmen flogging their product. Treat them as exactly that. They are only in it for the money, after all, and they are not going to point out the obvious causes of damp and suggest that you try to fix the gutters before spending your cash on a DPC.

 

[MikeG]

Rising damp exists. DPCs and DPMs are just one way of handling the issue.

Anyone who claims that rising damp doesn't exist is going to need to explain to me how a house which I built, and which I then lived next door to for 17 years, had dark damp bricks below the DPC on the plinth, and light dry bricks above (same bricks of course).....every winter, and not during the summer. The name of the village ended in "...marsh". It's a lovely little theory, and there are some really weak bits of research backing it up, when the reality is that I can walk people around this area, with a moisture meter in their hand if they want, and physically show them the phenomena in action.

I take it that by "moisture meter" you mean a device which does not measure the moisture content of a wall and which will give completely misleading results in most circumstances?

That's why I said "if they want". I have no use for them, and wouldn't trust one as far as I could throw it.

 

[MikeG]

........How high was the floor level inside the house?

Suspended beam and block floor probably a foot or 18 inches up the that wall at that point, but completely irrelevant to the dampness rising up the outer leaf to the underside of the DPC, and getting no further. The floor is suspended from the inner leaf, and isolated from the wall by a wrapped DPC. There is no damp in the house, but obvious evidence of it below the DPC externally.

How high do you think the water would rise up the wall without the dpc?

I'm not sure what this has to do with the question of the existence of rising damp, or the fact that it could only rise to the underside of the DPC in the case I described.

Obviously capillary action is a real physical phenomena but it is dependent on fluid and materials.........

I'm not following your argument. Are you saying that rising damp exists, or that it doesn't exist? You are accepting the root cause of rising damp, so it would be hard to see how you'd argue that rising damp doesn't occur.

......... I don't believe drilling holes in masonry, injecting something (silicone?), and cement rendering internally, which by definition wouldn't be needed if the chemical injection worked, is anything but destructive and fraudulent. It's looks like a cynical panacea preying on fear an ignorance to me....

I couldn't agree more.

 

[plasticpigeon]

I'm not denying the mechanism for rising damp, I'm afraid that is a straw man, but the question I am asking is if it is an issue. If a building is made of granite or slate I would put money on it not being an issue hence the material is important. I don't know about brick. I'm certain with vitrified bricks no water would rise. I have a hunch that with soft brick the water would rise but it wouldn't be a big issue if the wall wasn't covered in something impermeable. This is through limited personal experience of an internal wall in my house sitting on an earth floor without a dpc in the wall. It was covered in hardboard and was damp behinid. I lime plastered it and substituted the earth floor covered in quarries with a limecrete floor covered in quarries. Obviously this lowered the ground level by 18" or so. The wall is not damp enough for it to feel damp or cause any problems associated with damp so as far as a homeowner is concerned it is not damp. I'm not making a simplistic either or argument. It is more to what extent is it an issue, and I think it is overblown.

 

[MikeG]

Well we're talking past each other. I was refuting the claim that rising damp doesn't actually exist. I said previously that there are a number of ways of overcoming the issue, and having a DPC/ DPM is only one of them. I don't dispute anything else you are saying. We may even be in violent agreement with each other.

 

[plasticpigeon]

I think so!

 

[J_Ashley]

I thought I'd already posted this reply, but apparently not......

Thanks for all the advice and links - it's been an interesting read through.

Sounds like the DPC will be another “try to forget about it and move on with life”. Fortunately we don’t seem to be experiencing any damp problems, but it’s the uncertainty over potential future issues that remain a discomfort - I guess that’s all part and parcel of period property ownership. We don’t want to go to the expense/hassle of renovation to then have to redo things in the not too distant future because we ignored them now. Equally though, undoing some of this stuff would be highly damaging itself and very expensive, and, in reality, there is no obvious problem to solve – only peace of mind about the workmanship.

Unfortunately the repointing was also done in cement. It’s hard to know the date, and it could have been done around the same time as the DPC, but is potentially earlier (25+ years). We sought some advice and, fortunately, it doesn’t seem to be doing much damage. We were advised that removing it now would likely be more damaging than the minimal detrimental affect the cement repointing is currently having. Leaving it to naturally weaken over the years to make removal easier, and then repointing with lime seems to be the way to go.

It frustrates me that it takes ignorance by two parties - both the owners and the workmen - to commit these mistakes! Such unawareness seems even more surprising considering that (thankfully) a lot of the original features (sash windows, cast iron guttering etc.) were never replaced with modern plastic versions.