Breathability of floors

[leifinlisbon]

Hi there, I'm a new poster — and not located in the UK. I hope you can overlook that. My 19th-century home is located in Lisbon, Portugal, but there are few countries that do renovation as well as the UK. Certainly in Portugal there is little expertise or knowledge in this realm.

I'll cut to the chase: I'm really confused about breathability requirements of the ground floors of historic homes. I've been researching the issue for more than a year, and I'm more unsure than ever.

I'm of course aware of the dictum that old homes must breathe. And I'm aware of the impressive innovation in lime-based products and building techniques promoted by the likes of Mike Wye, Roundtower and Ty-Mawr. Until just this week, I had been full steam ahead on installing a Limecrete floor in my home, despite being considered a crazed, over-Googler by every builder whom I've interviewed. I was reassured when I recently discovered an industrious British couple that has been documenting on YouTube their backbreaking experience of installing Limecrete slabs throughout their home in Portugal.

(To be clear, I've been looking at Limecrete only for the breathability feature, not because I intend to install underfloor heating.)

Nevertheless, I'm now having doubts. I just became aware of a recent study out of the University of Bath that found that impermeable floors do not affect the moisture content of adjascent rubble walls. Another study found that limecrete slabs were only marginally more breathable than concrete slabs. Both were funded by Historic England. Its webpage summarizing the research grant stated: "It is a widely-held belief that if an impermeable ground bearing slab is installed in an old building, ground moisture will be ‘driven’ up adjacent walls. Although there are numerous references to this phenomenon, both in technical and product literature, they tend to be anecdotal and unsupported by scientific evidence."

In addition, I spoke today to the local sales rep for Diasen, an Italian company that is at the forefront of innovate lime-based products. They have two flooring products, Diathonite Thermostep.047 and Diathonite Screed, that boast high breathability with very impressive insulation values. Both, especially the Thermostep, are quite expensive. Yet the rep told me that their floor systems are typically installed with a liquid waterproofing and vapor-blocking product called WATstop underneath. I asked the Diasen rep why they would possibly advocate blocking the vapor permeability of floors when one of his company's main — and very expensive — value propositions is maintaining breathability. He responded by saying that while Diasen is singularly focused on breathability, walls are what really matter. Inhibiting their breathability is what has the potential to cause serious damage. But according to him, it is Diasen's position that floors in historic homes do not absolutely, 100% need to breathe. (I still don't get why someone would buy their pricey screeding products for a ground floor if breathability were not an issue, as a concrete slab with PIR underneath is much cheaper.)

All this is not even to mention the controversies over rising damp, with one camp promoting technology including magnets, and another camp saying that rising damp doesn't exist (and that the magnets are snake oil).

So what gives? Is the recent research somehow flawed? Is this only an issue in climate like Britain's, where the soil is frequently damp (a frequent retort by Portuguese builders)? Is underground water vapor (evaporating from the water table through the soil) really that big of a cause of rising damp or is it truly more about liquid groundwater and/or condensation of water vapor that enters the walls from inside of the house?

And how is the migration of moisture through traditional homes still so misunderstood?

 

[malcolm]

I have a bunch of concrete floors on my ground floor that are not so breathable. They work so long as the exterior ground level is 150mm lower than internal. That 150mm of outside wall does need to be breathable - lime not cement. If you've not got the underfloor breathable to outside already there will be a long drying time for the earth underneath the house to dry out.

I'm a fan of thinking about how to let the water out. If you have an older house with limited damp proofing you will have water getting in. The trick is deciding where you want to let the water get out. Releasing the water to the outside of the house is better than letting it into the house. Breathable floor is good if you can't do that and you want to stop the water coming up the walls. If you can't do anything about the walls then definately you need a breathable floor.

 

[leifinlisbon]

Thank you, @malcolm. I appreciate your insight. It's great to know that the position of the floor in relation to the outside wall is key to understanding how liquid and gaseous water will move under a sealed floor. Most of my house is at least 15cm above the adjacent ground, so I'm good on that front.

The tricky thing in my case is that I don't currently have an observable wetness issue. The house functions perfectly fine. I'm just nervous about messing with the historic fabric and creating a problem. At the same time, I don't want to overengineer a costly solution — a Limecrete slab is a bit of a risk if your builder has never even heard the term before.

I totally understand that it's important to let water out. As I understand it, once water gets into your walls (either through capillary action or through water vapor entering and condensing), the only way out is evaporation. That's why the breathability of walls is non-negotiable.

It makes some sense that the amount of ground moisture would be increased if 110m2 of flooring suddenly become unbreathable. Then again, we have a garden of 60m2 behind the house. Surely, its buffering role will make the impact on the walls relatively minor?

 

[leifinlisbon]

This is an exploratory hole in the floor:



In this room, we can see 3cm terracotta tiles (not original — they probably date to 1955) on top of a 4-5cm mini "slab". I assume the slab was made with quicklime and aggregates because of the large white clasts inside and the violent reaction when vinegar is poured on it. (Portuguese builders continued doing things "the old way" well into the 20th century.) Under that, around 1cm of fine leveling sand on top of bedrock.

In other rooms, there's no bedrock. The lime mortar bed is laid on round river stones laid on top of compacted earth.

The tiles have interesting perforations that I suspect might have been a 1950s solution to rising damp and/or salt attack:



A document from Heritage Victora out of Australia notes that perforated masonry units were used to control damp in the 19th century: Some of the most effective DPCs used were glazed hard-burnt ceramic tiles or bricks, often with perforations allowing ventilation (Figures 9 & 10). These DPCs were laid without mortar in the perpendicular joints to prevent moisture passage through permeable mortar. In pulling up the tiles, I might be inadvertently reversing a solution to past problems of damp.

So far, I've been considering a few options for the slab that will go under my new floor:

1. In the areas with bedrock under the floor, there's no room for a foam glass layer. So instead of Limecrete, in those zones I was thinking of applying an insulating lime-based mortar/screed such as Dianthonite Screed directly onto the stone. In areas where no bedrock is present, there is indeed room to do a Limecrete "2.0" slab (the version using foam glass instead of expanded clay)
2. Skip all the lime-based breathable solutions and let my Portuguese builders put in the cheaper, easier solution that they're comforable with: a thin vapor-impermeable concrete slab reinforced with a wire mesh
3. Keep the existing historic lime-based slab, accepting that I will always have cold floors, but possibly add a waterproofing agent such as WATstop on top to block capillary action

The new flooring that will go on top is a mix of large-format marble and travertine tiles.

Any thoughts or insights?

By the way, this video presentation is super informative on the latest scientific understanding of moisture issues in historic buildings.

 

[88v8]

Quite some research !

Our only experience of limecrete is in the sitting room where we inherited a 70s concrete floor with dpm, and the walls were damp. Indeed, the perimeter was so damp that the wooden Gripperods were rotting.

A leca/limecrete slab - this was 12 years ago - made the damp disappear.

Regards your house, I'm tempted to say that if it ain't broke... so if your floors are dry, leave well enough alone.
However, you may well break it if you lay impermeable finishes such as marble, especially with tight joints that afford no possibility of breathing.
On the whole, a tiled floor breathes through its joints, and needs to be bedded in lime and pointed in lime, otherwise you may find in a few years that you have shot yourself in the foot.

Ivor

 

[Cubist]

Ahhh, this one had me stepping back a long way to collect my thoughts and particularly how I want to present them. Apologies in advance if some of the following sounds a little patronising.

Your, my, our primary enemy is not damp. Damp is merely a front line ally of the greater enemy 'entropy' and stands shoulder to shoulder with thermal cycling as the roots of all decay. It is thermal cycling that promotes repeated expansion and contraction of materials and the extent of that expansion and contraction is influenced by how much moisture may be present in those materials at any moment in time. Were you to take two new bricks and place one inside an absolutely water tight environment and leave the other exposed to atmosphere you would not be surprised later to find that the latter has crumbled to dust - but leave the other a little longer and it too will end in the same way. This destruction is predominantly an effect of 'differential movement' within the brick albeit that external erosion may also play a hand.

Differential movement also plays a hand when disparate materials are placed in close proximity or are somehow bonded together. Indeed, the bonding material itself, say mortar, can play a major role and there are many examples of wals that have in effect pushed themselves apart because the bricks and the mortar expanded and contracted at different rates.

And this is where I get to the specific points I want to make concerning your situation and questions.

• Modern Portland Cement based concretes have a life expectancy measured in decades and steel reinforced concretes will fail much sooner. (Say NO to the steel mesh)
• Lime based mortars and concretes can last centuries and you can find many that have survived for millennia.
• There is a contention that many of the Roman lime concrete structures, e.g. the Pantheon, were constructed using a 'hot lime mix' process that appears to possess a 'self healing' function in which small cracks are repaired by internal chemical processes.
• Portland cement and lime based mortars and concretes are not good bedfellows. They will not bond well at the level of the interface between them and they will soon separate and one or the other may then begin to break up. (If your builder will not use lime then tell him the tell him 'Obrigado and bugger off!'

Ultimately we all face something of a balancing act insofar that we must encourage moisture, whatever its source, to migrate outdoors as rapidly as possible but we have to be careful about the various transition points between different materials as these may either prevent or seriously inhibit that flow and this contributes to the development of other problems like wet rot and beetle infestation among others.

 

[leifinlisbon]

Thank you, @88v8! Experiences like yours seem to confirm that a breathable floor is hugely helpful with damp issues. Looking at the research out of Bath, I see that they only made one room impermeable, not the whole house. That might be why it failed to capture an impact on wall moisture levels. And the other study only looked in a lab at the vapor permeability of chunks of concrete versus Limecrete, whereas what's underneath it — glass foam gravel/leca versus a DPM — are probably hugely determinative.

I hear you about not fixing what ain't broken. Yet the tiles themselves are in pretty bad shape (especially after my exploratory holes ha), so we are going to replacing the flooring material at the very least. The house is also extremely uncomfortable in winter as it has no heating, a not-uncommon feature even in nice houses in Lisbon, despite weather that's chillier than you might guess. So under floor insulation would be great if it didn't come at the cost of other problems.

It's my understanding that porous stones like limestone and travertine do have decent vapor permeability. Every room will be tiled 50-100% in porous stone. And I hear you that oversized joints and lime-based bedding and grout are important too.

Keeping in line with your advice, the least invasive option would be to keep popping the terracotta tiles off of that Roman concrete-style slab and just install the new stone flooring over that. The floors will continue to be cold, and there will continue to be thermal loss through them (8%, according to my house's energy rating study), but we won't need to wear winter coats on the ground floor once the heat pumps are operational. (Last winter it was so cold that we saw our breath most nights.)

Is the soil around your house generally damp? And do you have much exposed earth in the front and/or back of the house?

 

[leifinlisbon]

Has anyone heard about systems like this? It seems like a decent compromise to allow a vapor permeable perimeter yet add some kind of vapor impermeable layer in the middle of rooms.

In the context of my house, that could mean keeping the old lime slab, but adding a waterproofing expoxy just in the middle of the room,.

 

[leifinlisbon]

Ahhh, this one had me stepping back a long way to collect my thoughts and particularly how I want to present them. Apologies in advance if some of the following sounds a little patronising.

Your, my, our primary enemy is not damp. Damp is merely a front line ally of the greater enemy 'entropy' and stands shoulder to shoulder with thermal cycling as the roots of all decay. It is thermal cycling that promotes repeated expansion and contraction of materials and the extent of that expansion and contraction is influenced by how much moisture may be present in those materials at any moment in time. Were you to take two new bricks and place one inside an absolutely water tight environment and leave the other exposed to atmosphere you would not be surprised later to find that the latter has crumbled to dust - but leave the other a little longer and it too will end in the same way. This destruction is predominantly an effect of 'differential movement' within the brick albeit that external erosion may also play a hand.

Differential movement also plays a hand when disparate materials are placed in close proximity or are somehow bonded together. Indeed, the bonding material itself, say mortar, can play a major role and there are many examples of wals that have in effect pushed themselves apart because the bricks and the mortar expanded and contracted at different rates.

And this is where I get to the specific points I want to make concerning your situation and questions.

• Modern Portland Cement based concretes have a life expectancy measured in decades and steel reinforced concretes will fail much sooner. (Say NO to the steel mesh)
• Lime based mortars and concretes can last centuries and you can find many that have survived for millennia.
• There is a contention that many of the Roman lime concrete structures, e.g. the Pantheon, were constructed using a 'hot lime mix' process that appears to possess a 'self healing' function in which small cracks are repaired by internal chemical processes.
• Portland cement and lime based mortars and concretes are not good bedfellows. They will not bond well at the level of the interface between them and they will soon separate and one or the other may then begin to break up. (If your builder will not use lime then tell him the tell him 'Obrigado and bugger off!'

Ultimately we all face something of a balancing act insofar that we must encourage moisture, whatever its source, to migrate outdoors as rapidly as possible but we have to be careful about the various transition points between different materials as these may either prevent or seriously inhibit that flow and this contributes to the development of other problems like wet rot and beetle infestation among others.

Thank you, @Cubist. Not patronizing at all and very helpful.

You make a great point about the dangers of mindless mixing of materials. My understanding is that the most extreme example of this is re-pointing an old rubble wall with cement. And even the wrong type of lime mortar mix can mess things up quickly, no?

That's an interesting point about the steel mesh. I didn't know that. What do you think about acrylic fibers? Or are there non-metal meshes that are more appropriate?

Thank you also for that advice about avoiding applying Portland cement to layers rendered in lime. I'll be sure to avoid that.

Regarding Roman concrete, I read that recently too and found it fascinating. It's why I'm really hesitating to dig up the existing slab. (Believe it or not, the budgeting director at my builder didn't even know what quicklime is!)

Pretty much every old building in Portugal is being unintentionally destroyed when it's renovated. Builders are outrightly hostile to the idea that modern materials aren't perfectly suited to the job. Part of it is a famous culture of shortcuts and short-term thinking. Part of it economics — this is poor country that hasn't had the luxury of pricey conservation. And part of it is brain drain. Some of the world's best tradesmen are Portuguese, but few of them are still in Portugal.

 

[Cubist]

As is my want I sometimes go back over the content of a discussion to see if I've missed something and in doing so this time the tiles caught my attention.

You're right I believe that the tiles are a much later addition to the property. These would most likely have been produced using an extrusion process where the wet, heavily processed, clay is pushed through a suitable die and then cut to the desired length. I doubt though that salts or damp produced the patterns on the upper face of them. This, I think, were most likely printed/embossed on what would have been the underside of tiles as they were transported away from the press on a conveyor belt. The conveyor belt itself would have been strewed with sand to prevent the still wet and highly plastic tiles sticking to the belt itself and this would have produced an entirely random pattern of indentations in what would become the face of the tiles.

You make a great point about the dangers of mindless mixing of materials. My understanding is that the most extreme example of this is re-pointing an old rubble wall with cement. And even the wrong type of lime mortar mix can mess things up quickly, no?

That too is true, but theres a much better chance of getting the old and new to bond and co-habit.

What do you think about acrylic fibers? Or are there non-metal meshes that are more appropriate?

I haven't used them, but others here may have done so and will comment, the problems with steel is corrosion and the rate of expansion and contraction, particularly in fairly thin depths of concrete. I would chi to see if there are any negative chemical interactions with the chosen concrete before deciding which re-inforcement to use.

(Believe it or not, the budgeting director at my builder didn't even know what quicklime is!)

No surprise there, sadly such ignorance is not uncommon.

Pretty much every building in Portugal is being unintentionally destroyed when it's renovated. Builders are outrightly hostile to the idea that modern materials aren't perfectly suited to the job. Part of it is a famous culture of shortcuts and short-term thinking. Part of it economics — this is poor country that hasn't had the luxury of pricey conservation. And part of it is brain drain. Some of the world's best tradesmen are Portuguese, but few of them are still in Portugal.

That too is sad and, again, not uncommon. Portugal was a key part of my personal bailiwick when I was accountable for Southern Europe in one of my professional incarnations but never got to know it terribly well.

That said, I know that sometimes Lisbon can receive a lot of rainfall but mostly it is rather warm, much more so than back here in the UK. With this in mind I am puzzled, particularly as your house stands on granite, why you are so concerned about rising damp and are considering adding any kind of impermeable layer, however limited, above it?

Frankly, in your shoes, I think I would be focusing on simply making the floors good while ensuring I did not introduce anything that could inhibit moisture movement.

 

[leifinlisbon]

You're right I believe that the tiles are a much later addition to the property. These would most likely have been produced using an extrusion process where the wet, heavily processed, clay is pushed through a suitable die and then cut to the desired length.

Oh nice, that's interesting to know. Thank you.

I doubt though that salts or damp produced the patterns on the upper face of them.

Actually, the photo is deceptive. The tiles are covered in dust from the grinder. In fact the surface is fairly regular except for years of lindseed oil and dirt having built up on them.

That said, I know that sometimes Lisbon can receive a lot of rainfall but mostly it is rather warm, much more so than back here in the UK. With this in mind I am puzzled, particularly as your house stands on granite, why you are so concerned about rising damp and are considering adding any kind of impermeable layer, however limited, above it?

It's a fair question. I would love for an authority tell me that I don't have to worry about these issues in Portugal.

It's certainly possible that I went down a rabbit hole and got misinformed along the way. Like I said, I've had trouble finding a specialist here who seem to know what they're talking about. Instead I've had to fall back on my own research. Most of the best resources on historic renovation online come from the UK, and moisture seems to be an eternal vexation for you guys. It occurred to me that this could just be a British problem given your climate, yet usually this is described as a function of old building modalities/materials and the water cycle, so it seems more universal than that.

First, just to clarify, you're right at least some parts of the floor rest on stone, but I don't know how much. It could be entire rooms, or it could be just that hole I made. (I think the stone is limestone, not granite, but I'm no expert.) Underneath the floor in other rooms we just found bare earth. In one of those latter holes, the earth was quite moist in winter. I'm not sure if that was because of a leaking pipe somewhere nearby or soil moisture from precipitation.

Lisbon gets a surprisingly decent amount of rain: an average of 100mm in Oct, 127mm in Nov, 126mm in December, and 99mm in January. (Last December, we got 65mm in just three days!) London, for just one comparison, gets 67, 66, 59 and 59 respectively.

The terracotta tile skirting that lines the walls shows significant damage over time from dampness and salts. They're splotchy white and crumbling away in many places. There's also bubbling plaster one one exterior wall, presumably from past dampness, although this might have been caused by a leak as opposed to rising damp.

We have a well in the back that still produces water — we use it to fill the pool and water the plants. Most houses in our little neighborhood have wells. It seems the aquifer is substantial.

My upstairs neighbor shares one external wall with me on the ground floor. (He has the top two floors of our building, which was once a big grand family house, and I have the bottom two floors). He totally gutted the place over a two-year project. It was all modern materials — he's never heard of breathability. Lo-and-below, the paint on the exterior wall next to his staircase is starting to bubble. His builder told him they need to apply even more waterproofing to the exterior walls to keep the water out of his apartment.

I have also heard from my architect and various builders that salt efflorescence is a not-uncommon occurrence in Lisbon, especially because the sand used in mortars was traditionally picked up right from the ocean and used directly. I've been in old houses for sale here where the smell of mold and mildew is overwhelming, and probably never going away.

So I'm not totally sure. This whole enterprise is hard because it's all theoretical and mostly based on resources from other countries/climates. Right now the house is dry. But I would hate to go to great expense fixing it up, only to introduce a new major problem.

Frankly, in your shoes, I think I would be focusing on simply making the floors good while ensuring I did not introduce anything that could inhibit moisture movement.

This sounds wise. In this case, I think that would mean using the grinder to take off those old clay tiles, but leaving the Roman-concrete-style slab, and then laying the new stone tiles directly on top with no waterproofing and only lime-based adhesive and grout?

 

[Lacan07]

View attachment 11163


Has anyone heard about systems like this? It seems like a decent compromise to allow a vapor permeable perimeter yet add some kind of vapor impermeable layer in the middle of rooms.

In the context of my house, that could mean keeping the old lime slab, but adding a waterproofing expoxy just in the middle of the room,.

Interesting, I guess the question to ask yourself is will the moisture have a suitable area to escape from before it considers going sideways into the walls.

You see similar versions of this over here where people have dug out a trench around the perimeter of a room and filled with stones, kind of like an interior french drain. There's an old shop in the town near me that has one.