My wife and I have bought a villa with a basement from 1924 outside of Stockholm. We would like to convert the basement's three rooms into a laundry room/spa, a computer room, and a guest room. However, we first need to address the moisture problems and the basement smell present in the basement (We also have a radon issue, but that's another matter). These are the conditions:
-Concrete slab of 10 cm directly on soil
-The concrete slab is very uneven and sloped
-All organic materials have already been removed
-Masonry concrete walls that are fairly dry. Drainage performed about 30 years ago
-The concrete slab is super damp. If you spill water, the spot does not dry for several days.
-A dehumidifier has been running on "Sahara mode" for the past 2 weeks. The basement smell is still present.
-Limited building height, at least 2.04 from the concrete slab to the ceiling joists
I'm absolutely not keen on renewing the drainage if it can be avoided. I'd prefer to postpone that expense for a few years. Likely it works okay as the walls are dry. The concrete slab is probably the main cause of the moisture in the basement. I'm also not keen on breaking up the existing slab and doing the job properly with insulation and a moisture barrier under the concrete slab. I have looked at ventilated flooring, platon, and nivell, but the costs are high and it adds height.
What I'm considering is placing a moisture barrier on the existing slab in the form of a moisture-resistant plastic film and then using self-leveling compound on top of the moisture barrier to create an even and dry slab where I can later lay carpet and limewash in the laundry room. The moisture can then run rampant in the lower slab, but it won't rise into the house because of the moisture barrier. The moisture barrier would also seal the house and might reduce radon leakage, although this is not the primary goal. This solution would mean I need to build very little in height, which is a big plus. I've never heard of anyone doing something similar. Do you see any problems with this solution? Very grateful for any response.
-Concrete slab of 10 cm directly on soil
-The concrete slab is very uneven and sloped
-All organic materials have already been removed
-Masonry concrete walls that are fairly dry. Drainage performed about 30 years ago
-The concrete slab is super damp. If you spill water, the spot does not dry for several days.
-A dehumidifier has been running on "Sahara mode" for the past 2 weeks. The basement smell is still present.
-Limited building height, at least 2.04 from the concrete slab to the ceiling joists
I'm absolutely not keen on renewing the drainage if it can be avoided. I'd prefer to postpone that expense for a few years. Likely it works okay as the walls are dry. The concrete slab is probably the main cause of the moisture in the basement. I'm also not keen on breaking up the existing slab and doing the job properly with insulation and a moisture barrier under the concrete slab. I have looked at ventilated flooring, platon, and nivell, but the costs are high and it adds height.
What I'm considering is placing a moisture barrier on the existing slab in the form of a moisture-resistant plastic film and then using self-leveling compound on top of the moisture barrier to create an even and dry slab where I can later lay carpet and limewash in the laundry room. The moisture can then run rampant in the lower slab, but it won't rise into the house because of the moisture barrier. The moisture barrier would also seal the house and might reduce radon leakage, although this is not the primary goal. This solution would mean I need to build very little in height, which is a big plus. I've never heard of anyone doing something similar. Do you see any problems with this solution? Very grateful for any response.
In fact, most of the moisture in a basement comes from within. This is because warm air can hold more moisture (in the form of water vapor). When the warm air meets the cold in the concrete floor or masonry wall, the water vapor condenses in the wall/concrete. As long as you don't have more than 16° in the basement, it's not a big issue. If you lay plastic on top of the concrete floor, the condensation will occur on the top side of the plastic.
The only really good solution is to insulate walls and floors from the outside. If you need to insulate on the inside, you must use materials that can withstand moisture and never enclose them with plastic sheeting.
Your house is probably constructed with so-called spread footings, which are concrete beams located under the walls. Between these spread footings, a thin concrete slab has been cast. It is not particularly difficult to break up such a thin concrete slab, insulate, and pour a new one.
The only really good solution is to insulate walls and floors from the outside. If you need to insulate on the inside, you must use materials that can withstand moisture and never enclose them with plastic sheeting.
Your house is probably constructed with so-called spread footings, which are concrete beams located under the walls. Between these spread footings, a thin concrete slab has been cast. It is not particularly difficult to break up such a thin concrete slab, insulate, and pour a new one.
I have chipped away half a basement with about a 15cm concrete slab. It's not something I would do by hand again. I agree with Justus in what he says. What you can do is drive away the moisture with, for example, underfloor heating. However, many say that the moisture then travels up into the walls. Personally, I would have blasted all walls and floors from old paint and painted anew. Also replaced the ceiling. I think a lot of the smell you sense will disappear then. Then make sure everything can breathe and run the dehumidifier at max. However, I wouldn't spend too much money on expensive decor until the drainage issue is resolved. I think it is quite common this time of year that the water doesn't dry in basements that aren't constantly heated and well ventilated. We use black/dark gray "patio mat/artificial grass" in a room in the basement. Maybe not the prettiest, but nice to walk on, reasonably easy to clean, cheap, and the moisture and water go straight through (annoying when you spill).
Thank you for your reply Justusandersson. I believe I have control over the moisture coming from the inside through ventilation and a dehumidifier if required. When I measured relative humidity, it was specifically the floors that stood out, the walls were okay. Doesn't that indicate that moisture is traveling upward through the thin concrete slab?
So what I'm thinking is to embed a moisture barrier between the old slab and the new layer of self-leveling compound. On top, a breathable carpet will be laid. The moisture from below should be kept away with the help of the barrier and the moisture from the room should be ventilated out or handled by the dehumidifier.
The most aesthetically pleasing solution would probably be to break up the slab and insulate from underneath as you suggest. With such a solution, I would get a better insulated floor and gain a few centimeters in ceiling height, but on the other hand, it requires a lot of work and the risk of undermining the house if professionals are not hired. I am leaning towards, after all, installing a moisture barrier and casting on top of the moisture barrier...
So what I'm thinking is to embed a moisture barrier between the old slab and the new layer of self-leveling compound. On top, a breathable carpet will be laid. The moisture from below should be kept away with the help of the barrier and the moisture from the room should be ventilated out or handled by the dehumidifier.
The most aesthetically pleasing solution would probably be to break up the slab and insulate from underneath as you suggest. With such a solution, I would get a better insulated floor and gain a few centimeters in ceiling height, but on the other hand, it requires a lot of work and the risk of undermining the house if professionals are not hired. I am leaning towards, after all, installing a moisture barrier and casting on top of the moisture barrier...
J justusandersson said:
In my ears, it sounds risky to experiment with such solutions instead of using proven products such as a leveling floor or the suggested solution to chisel, insulate, and pour.
"Own" solutions unfortunately tend to be both inferior and more expensive.
Now I don't know what kind of moisture barrier you're considering, but you should probably ensure that the one you choose can withstand being poured on so the chemical processes of the concrete don't risk damaging the waterproofing layer.
"Own" solutions unfortunately tend to be both inferior and more expensive.
Now I don't know what kind of moisture barrier you're considering, but you should probably ensure that the one you choose can withstand being poured on so the chemical processes of the concrete don't risk damaging the waterproofing layer.
Only if the slab is standing in water and then through capillary action, but it's very unlikely. Moisture bound in air as water vapor tends to move from warm to cold. Water vapor can move upwards through a concrete slab, but that occurs when it's heated by underfloor heating that is then turned off. The fact that the relative humidity in the basement isn't abnormally high is no guarantee that the water vapor in the air doesn't condense when it gets cooled by the cold concrete slab.jakazoid said:
I agree with mexitegel and Jonathan79.
A few years ago, I fixed up a room in the basement and am currently working on another room. Jackhammered, dug out, new capillary breaking material and insulation. Concrete slab with underfloor heating on top of that. It creates a completely new environment in the rooms.
Moreover, it's a good opportunity to lay down sewage pipes and other conduits under the slab while you're at it, which makes the rooms more pleasant and reduces the risk of hitting your head on hanging pipes. If you're lucky, you might be able to lower the floor a bit and thereby increase the ceiling height as well.
Sure, it's a really tedious job, but if you spend a couple of hours every evening jackhammering and digging, it's manageable.
Undermining the house isn't a risk as long as you don't dig below the edge of the footings. Make a small test pit and dig along the wall down to the edge of the footings to find out how much depth you have to work with. At least around 30cm is good if available.
Moreover, it's a good opportunity to lay down sewage pipes and other conduits under the slab while you're at it, which makes the rooms more pleasant and reduces the risk of hitting your head on hanging pipes. If you're lucky, you might be able to lower the floor a bit and thereby increase the ceiling height as well.
Sure, it's a really tedious job, but if you spend a couple of hours every evening jackhammering and digging, it's manageable.
Undermining the house isn't a risk as long as you don't dig below the edge of the footings. Make a small test pit and dig along the wall down to the edge of the footings to find out how much depth you have to work with. At least around 30cm is good if available.
If you block the moisture's path up from the slab with a tight layer, it only has one way to go... Up and out into the walls instead.
Lay Platon or equivalent on the concrete and mechanically ventilate it under negative pressure.
On the Platon mat, you can self-level but leave space for the air via a ventilated baseboard.
Lay Platon or equivalent on the concrete and mechanically ventilate it under negative pressure.
On the Platon mat, you can self-level but leave space for the air via a ventilated baseboard.