De-tanking a converted Victorian mill building?

[Galen]

I purchased a ground floor flat in a converted Victorian era mill building about 1.5 years ago. Unfortunately since then a penetrating damp problem in a corner of the building has come to light (amongst a number of other problems). Since buying the flat I've learnt a lot about solid wall buildings and how they're very different to modern buildings and require different treatment, materials etc.

If anyone is curious, the issue with penetrating damp is due to the ground level outside being higher than inside by roughly 1-2 brick courses. The management company are installing a french drain and also installing an injected DPC internally at the floor level (I know injected DPCs are somewhat controversial, but being done internally in the mortar at ground level, I can't see what the harm is?). Picture below showing the high ground level, efflorescence, and deteriorated mortar:


The other side of this corner is a north facing wall that doesn't get any sunlight. Again the ground level is too high on the left corner, and it looks like there's quite serious efflorescence under a pipe of some sort (no one seems to know what this pipe is for, and I've never seen it actually expelling water) plus damp bricks along the bottom. There are actually 3 DPCs on this wall if you look closely, which indicates to me that there have been persistent problems here, and the management company has just tried the same wrong solution at least 1-2 times ...


Internally the bricks are quite visibly damp at the base of the wall, but as the walls have been tanked internally with a cement render, it's difficult to know how far up the wall the dampness extends (although presumably as the exterior bricks don't look too bad, maybe not that far?)







The building was converted to flats in the 80s, and I think a lot of these problems have been caused by a bit of a botched conversion (high ground levels, injected DPCs, poor plumbing, no windows or extractor vents in kitchens, internal cement render etc.).

I'm quite keen to remove the internal cement render and then re-plaster these brick walls with lime plaster internally, the questions I have about this are:

1. How high is the risk of damaging the brickwork? I don't know what condition of these bricks is like, but judging from the exterior brickwork I would assume they're in OK condition.
2. How difficult would this be? Is it something I could DIY? I've had a look online and it looks possible, but it seems to depend how well bonded the cement is, and what sort of condition it's in (it seems pretty tough to me, but I'm really far from an expert here).
3. Is this actually worthwhile to do? And if so, how do I convince the management company? Most information I can find online pertains to external cement render (e.g. https://www.spab.org.uk/advice/lime-renders-vs-cement-renders) and not internal cement render.
4. If I don't remove the cement render, and assuming it runs say half way up the wall, would it still be worthwhile stripping the gypsum plaster back and re-doing it in lime? Or does the cement render largely make this a pointless endeavour?
5. Would it be worthwhile not plastering these walls at all (i.e. just stripping it back and leaving them as bare brick internally)? Presumably they would have been left as bare brick internally while the property was a working mill (unfortunately I can't seem to find any images of the inside pre-conversion). The walls are a brick and a half thick, so slightly thicker than most Victorian properties. Plastering would offer some small insulation advantage, but I'm willing to forgo that benefit if it means better humidity management.

I've had hygrometers in the property for the last year or so now. The only way to keep the RH inside anywhere below 60% is basically to have a dehumidifier running 24/7. Opening the windows when outdoor humidity is low helps for a few hours, but the humidity quickly shoots back up again. I'm aware this is being exacerbated by the damp bricks shown above, but I'm keen to do anything that will help with this, and I'd like to break the cycle of bad practice here by actually implementing solutions that are sympathetic to letting the building breathe inline with how it would have been designed to work originally.

 

[Cubist]

it looks like there's quite serious efflorescence under a pipe of some sort (no one seems to know what this pipe is for, and I've never seen it actually expelling water) plus damp bricks along the bottom.

If you mean the small diameter, circa 25mm, white PVC pipes at approx 2 meters above ground then these are overflow pipes servicing cisterns and basins installed on the first floor and above. Water would only be expelled through these due to over-filling of a bath or basin or, in some instances a failing valve in a toilet cistern.

Your management company is doing the right thing by installing a French Drain but I cannot say I agree their suggested DPC approach. Based on your photos I would suggest that they also need to re-point the lower courses of brickwork given the degree of mortar degradation. They should also be encouraged to use a lime based mortar to effect these repairs if it is established that the extant mortar is NOT cement based. Differential movement between these materials can be quite significant and lead to greater damage to the walls structure and the bricks themselves.

One of the issues with ground floor domiciles such as yours, and say a bungalow, is that the need for enhanced security often translates into windows and doors being kept closed at almost all times. As a consequence air-flow into and through these spaces can be less than optimum and result in moisture generated by the occupants being absorbed into the fabric of the structure itself. If there is no efficient means for that moisture to escape to the outer environment it will reveal itself in internal damp that cannot be traced back to any obvious water source and could potentially result in health hazards such as black moulds.

With that in mind I would suggest that, unless you are absolutely convinced that your flats problems are due to 'penetrating' damp from outside, then you would be wise to ensure that all kitchen and bathroom extractor fans are working efficiently and at all appropriate times. Also, any and all air-bricks should be checked and cleared of any obstructions.

 

[Galen]

Thanks for your reply, and explanation about the PVC pipes in one of the pictures I shared.

I agree with you that some of the brickwork needs need attention (there are actually some bricks that need replacing). I have mentioned this to the management company, and they thankfully are already aware of the importance of using lime mortar rather than cement based mortar, so that's positive.

The survey I had done came to the same conclusion as you - inadequate airflow due to the flat being ground floor. I have been opening the windows when I can for 15-30 minutes (whenever the outdoor humidity is low and I'm passing by the flat). Realistically this has been a couple of times a week over this summer.

The problem is that I've had the entire flat essentially gutted (there was water damage to almost all the internal studwork from various leaks) and replaced, but despite having a dehumidifier on 24/7 for weeks now, there's still a persistent damp smell in the property. I'm wondering if this is perhaps related to the internal walls being gypsum plastered and then left to dry with no ventilation for 3-4 weeks. That's the only other thing I can think of apart from the penetrating damp (the property hasn't been lived in for 2 years now, and the water supply is literally turned off, so there's no other source of moisture here), and is why I'm taking the penetrating damp so seriously - there are no other signs of damp or mould in the flat apart from the penetrating damp in that corner of the flat.

 

[aockenden]

Yes the cement render can be hacked off the underlying bricks. Yes it can be done by a competent and thoughtful DIYer.

Yes, depending on how well-adhered it is, it may damage the underlying bricks. If you’re lucky it’s already delaminated and will just fall away in big sheets. If you’re unlucky it’ll be fully adhered and tear up / pull off the faces of the bricks as it gets chiseled / SDS’d off.

Yes it’s probably worthwhile for the health of the building, especially in a damp hotspot and if you cannot resolve the high ground levels externally. That being said, I would never dream of doing it FOR a landlord unless they were paying me through the nose. Removing hard cement render is a big, dirty, nasty, labour intensive job which is tough on the body in multiple ways.

Just redoing the top coat of Gypsum in Lime might give you some minor benefits in terms of managing internal condensation problems, but I wouldn’t expect it to resolve any issues of damp penetration from outside until you’re fully breathable through every layer of the wall. And even that’s not the ideal way to handle it: reducing the exterior ground levels is.

My suggestion would be to get management to actually lower the ground levels (assuming their install of the French drain doesn’t lower them) and improve the external brickwork pointing, and also try to pin down what the deal is with that pipe. Once all that has been squared-away for a year and the issue is still not improving, then you can look at the next steps of removing cement internally.

 

[Stevers]

Those overflows could be for WC cisterns, the ball/diaphragm valves for these may develop slow leaks that overfill the cistern and lead to the overflow running. Each time the loo is flushed the overflow stops running, and that can mean that it is rarely caught running during the day, but can run for much of the night or when no-one is around to see it. This may also happen with the ballcock on cold water storage tanks Use of water in the house temporarily stops the overflow, but it can still run during times of almost zero water usage.

 

[DaveG]

Looking at the pictures there the exterior wall is already full of injected chemicals which people are starting to realise do cause long term problems. As these chemicals eventually degrade, moisture gets into these holes and overtime the bricks break down.
It’s likely that the damp caused by higher ground levels is the primary cause of the breakdown of those bricks and their mortar but it wouldn’t surprise me at all if the previous injections have actually accelerated the issue too.
Filling them with even more chemicals is not going to help.

 

[Cubist]

I've been mulling over your damp problems and suspect that internal leaks and water penetration through the brickwork may not be the full root cause. Mill buildings built in the Victorian period were constructed with ground floors to withstand the weight of heavy equipment and the regular movement of large and perhaps also heavy loads. As a consequence these needed to be massive, resilient, well constructed and, in the absence of both cement based concretes and the means to mix and pour these in very large volumes, would be constructed using layers of stone slabs, tiles, bricks and the like bound in a matrix of lime mortar. These floors, of course, would not include a DPM unless perhaps the matrix included a bed of slate. Therefore, and unless the developers who divided the mill structure into flats were obliged to remove the old floors and replace them with modern poured concrete, those ground floors would be a significant source of groundwater rising into the building from below. I think that most property developers would take the line of least expense where possible and simply pour fresh concrete over the existing floors with the aims of stabilising the old floor and establishing a new consistent level surface to support construction of dividing walls and partitions. The last photo you supplied seems to bear this out as it appears to show the remains of air bubbles that rose while the concrete was initially settling and commencing the curing process. However, these could also result from the use of one of the commonly available 'self levelling' compounds to establish the final floor level and surface ready for carpeting and tiles.

Whatever; such massive flooring structures would be capable of absorbing very large quantities of water, arriving into them from any avenue, that would then try to find its way out by whatever means may be available. And sadly, here I think is the rub for you. In effect the dehumidifier you are using is drawing moisture, absorbed into atmosphere from all the surrounding surfaces including the floor BUT the 'well' of water contained by your floor extends to the total footprint of the building!

 

[Galen]

Hi all,

First of all, thanks for all of your responses. I've already learned a few new things which is good (in my mind!).

To be clear - I own the flat as a share of freehold, so any improvements made would be to my benefit as well as to the buildings longevity.

To give a bit more background to the issue, the base of the affected wall does have some sort of foundational cement of some sort (I don't really know how else to explain it). There was a pond very close to this wall previously if not right next to it, so my assumption is that this concrete runs quite deep.

The surveyor and builder that came to look at the foundations concluded that the foundations here are very shallow, but I've since got other opinions completely to the contrary (and also, how could the foundations here be shallow when there are 3 stories above being supported by this wall!?).

I've attached a picture below to try and show this sort of concrete foundation. It's not the best, but it also shows where it was excavated to try and determine the depth of the foundations. There is soil on most of this concrete slab which unfortunately obscures it from view in this pat of the building (this will all be cleared away when the french drain is installed):



@Cubist - Thanks for your reply, that's really interesting. Unfortunately I can't seem to find any pictures of the inside pre-conversion, and despite my best efforts, I've been unable to find out what the floor or indoor condition would have been like pre-conversion (I even talked to a builder who used to come here as a teenager when the mill was derelict pre-conversion, but he couldn't seem to remember much about the actual material state of the building unfortunately).

All I know is that my section of the building was completed around 1890, and includes substantial metal pillars and wooden beams alongside the brick and a half thick walls. The metal pillars seem to have a base that meets the current flooring quite nicely, so perhaps the historic flooring actually wouldn't have been much deeper?

Whatever the state pre-conversion, the floor post-conversion is some sort of concrete/screed. Onto which was glued hardwood flooring (which unfortunately has since been ruined by the damp problems).

Assuming you're right about the floor being a big source of moisture, do you have any ideas what could be done to try and remedy or manage this? Are you saying running a dehumidifier is likely to be counter productive in this instance? Are you saying that the ground level around the whole exterior needs reducing (I think unfortunately the ground level all around has crept up a few cm during the conversion)?

Beyond lowering the ground level outside + installing a french drain, I am going to try and pick off some of the plaster to see how high the cement render runs inside. I think I need to do everything possible to try and combat the problem here.

If anyone else has experience with removing this sort of cement render I'd be happy to hear more about it, because I think unfortunately this would have to be a DIY job for me.

 

[Cubist]

Cast iron pillars spanned by either heavy wooden and/or iron beams were fairly common in these kinds of structure and were used to support the upper floors. Hardwood parquet was also fairly common in some ground - floor areas but this was typically restricted to office spaces rather than those where manufacturing or processing would be carried out.

I didn't mean to imply that the dehumidifier may be of little use - merely that it alone may never be man enough for the potential scale of the task.

You need to be careful when attempting to remove the cement base render from the walls. The render can be very hard and the bricks could be quite soft. As a consequence there is a significant risk of damage to the brick ranging from cosmetic surface injury up to its complete destruction.

With something as massive as the old floors and the surrounding foundations there will be no economically viable short term solution to the damp problem. In my view the only meaningful strategy would be to provide as many routes as possible to ensure effective transfer of internally generated moisture to external atmosphere whilst also ensuring that all land around the structure encourages and supports effective drainage of water from any source away from site.

 

[Galen]

The hardwood flooring is a bit of a mystery to me. The mill building was used for battery farming chickens inbetween it's life as a mill building and the conversion to flats, which to me would suggest the flooring would have been completely ruined. The poor job done with the conversion (which I think was in large part due to the motivation of cutting costs) makes me think it unlikely they would have chosen hardwood flooring as it is one of the more expensive floor types. I'm trying to see if I can get more pictures of the building (inside and out) as I know they exist somewhere in the local community, so maybe I'll find out at some point.

And thank you for your notes on the cement render; I'll proceed with caution. I suppose there's a small chance that I get lucky and the render doesn't reach far up the wall, in which case I may just strip back the gypsum plaster and re-do it in lime.

I'll talk to the management company more generally about what you've recommended - trying to ensure effective drainage away from the building wherever possible (unfortunately some of the land surrounding the building slopes towards the building, which is completely counter-productive and needs changing. I have discussed this with them already and I think this may even be considered as part of the french drain work).

When you say trying to "provide as many routes as possible to ensure effective transfer of internally generated moisture to external atmosphere" - did you have any specific ideas in mind? Or just you just mean making the building more breathable in general?

I'm aware that good ventilation is important, and I'm also going to submit an application to the local council to get an extractor fan fitted for the kitchen (another corner cut during the conversion) which I'm hoping they'll approve.

Beyond that and the potential of replastering internally in lime, I'm not sure what else can be done from an internal perspective.

 

[Stevers]

The mill building was used for battery farming chickens

Chicken effluent would be an excellent source of salts, and the original floor and walls could be heavily contaminated.

 

[Cubist]

ensure effective transfer of internally generated moisture to external atmosphere" - did you have any specific ideas in mind? Or just you just mean making the building more breathable in general?

Nothing specific but ensuring that all bathrooms, kitchens and laundry rooms being equipped automatic extractor fans would be a good contribution. Also, if the flats do not already possess them then carefully sited air-bricks in both the flats and communal areas would also be advantageous.

Stevers advice regarding chicken waste is indubitably correct. But the floors, such as they may have been, would not have suffered much direct physical damage. Any such would be due mostly to the caustic effects of the manure and the accumulation of salts as Stevers says.

Don't right off the possibility of hardwoods too quickly. Oak was abundant and fairly cheap and was a common material used in parquet floors in many public and private buildings. I remember the caretaker having to refresh the varnish each year in every assembly room, class room and office at the schools I attended.