We are now at the starting point of restoring our previously moldy-smelling and 5-months-ago gutted rec room and plan to start with the walls. Those who don’t want to read about drainage can skip to section 2 where my questions will appear. I know many are now thinking, "have you done drainage?" so we’ll start with that. Our Myresjöhus from 1974 has never been drained, and it will likely be a bit damp in our basement even now in the summer due to capillary forces combined with poor moisture protection on both floors and walls. Two moisture technicians (I didn't dare trust just one after reading probably 100 threads here on byggahus where the solution was often drainage...) independently thought drainage would be throwing money down the drain in our case since we wanted plastered walls and mechanically ventilated floors. The second moisture technician even asked me to get down to earth when I was rambling about damp wall plates on top of our bone-dry basement walls (which were also covered by a wall paper 
). After moisture measurement of the bone-dry plate, which he initially thought was redundant, he diagnosed me with "byggahus anxiety." He felt people should come to him before they started googling a lot, which only caused unnecessary anxiety and insomnia (Check). There is definitely something to what he says, but we always want to google, right?
SO we have opted to hold off a bit on the tedious drainage. Hopefully forever, but I promise to reconsider if the plaster starts falling off the walls. Now to questions.
Currently, there are concrete block walls finished to decent smoothness, but I plan to even out the surface a bit by plastering over the existing plaster. There are a few minor cracks that I have started to chisel out with a screwdriver and hammer, but otherwise, I think the plaster holds well. I’ve been going around gently tapping here and there but find no loose plaster.
1. Firstly, should you chip off plaster from a concrete block or should you scrape it? I feel the concrete block breaks apart and is very porous behind, and I wonder if it’s because I'm chipping away plaster that actually feels considerably more durable...
2. I have found out that it’s important to know the class of plaster to match with new plaster. But how on earth do I find out what plaster I have in a basement built in 1974? It might be in the building plans, but I don't know if I want to rely on these...
4. Can I use the same material in my chipped crack as when I am smoothing out the whole wall?
5. I have hammered in some old remaining nails about 1 cm. Right/Wrong? Most came out when I pulled out the studs. Some nails pulled out probably 5 cm of plaster, but others are just small holes. How should I fill these holes?
6. Other good tips are received with great appreciation as I am a beginner and completely inexperienced!
). After moisture measurement of the bone-dry plate, which he initially thought was redundant, he diagnosed me with "byggahus anxiety." He felt people should come to him before they started googling a lot, which only caused unnecessary anxiety and insomnia (Check). There is definitely something to what he says, but we always want to google, right? SO we have opted to hold off a bit on the tedious drainage. Hopefully forever, but I promise to reconsider if the plaster starts falling off the walls.
Now to questions.Currently, there are concrete block walls finished to decent smoothness, but I plan to even out the surface a bit by plastering over the existing plaster. There are a few minor cracks that I have started to chisel out with a screwdriver and hammer, but otherwise, I think the plaster holds well. I’ve been going around gently tapping here and there but find no loose plaster.
1. Firstly, should you chip off plaster from a concrete block or should you scrape it? I feel the concrete block breaks apart and is very porous behind, and I wonder if it’s because I'm chipping away plaster that actually feels considerably more durable...
2. I have found out that it’s important to know the class of plaster to match with new plaster. But how on earth do I find out what plaster I have in a basement built in 1974? It might be in the building plans, but I don't know if I want to rely on these...
4. Can I use the same material in my chipped crack as when I am smoothing out the whole wall?
5. I have hammered in some old remaining nails about 1 cm. Right/Wrong? Most came out when I pulled out the studs. Some nails pulled out probably 5 cm of plaster, but others are just small holes. How should I fill these holes?
6. Other good tips are received with great appreciation as I am a beginner and completely inexperienced!
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Is the render painted today? Are you planning to apply a layer of render to the entire wall, or is it enough to just spot-treat where it's needed to even out?
Your approach to drainage sounds reasonable to me. I think the drainage obsession on byggahus is largely due to many people in their 40s/50s wanting to realize their dreams and build home theaters in the basement ("for the kids"). In that case, you want a good indoor climate, but if the basement is only going to be used as intended, a bit of moisture or subpar insulation doesn't matter as long as you ensure good ventilation and materials that don't trap moisture.
Your approach to drainage sounds reasonable to me. I think the drainage obsession on byggahus is largely due to many people in their 40s/50s wanting to realize their dreams and build home theaters in the basement ("for the kids"). In that case, you want a good indoor climate, but if the basement is only going to be used as intended, a bit of moisture or subpar insulation doesn't matter as long as you ensure good ventilation and materials that don't trap moisture.
I had repaired cracks and holes with a C kc 0-3 mortar and then fine-plastered the walls with C kc 0-1 mortar. If there is paint on the walls, they must be sanded. Water the surface generously before plastering and rent a mixer so you can mix a few bags at a time.
It is unpainted plaster today that I will try to smooth out. A straight plank reveals that it is quite uneven and can vary a couple of centimeters in the plaster over a couple of meters. So I will probably plaster most of the wall to make it as even as possible.
I'm worried that I'll use the wrong plaster and everything will fall off the wall since I don't know what it is plastered with today =(
C kc 0-3 mortar in cracks and C kc 0-1 mortar for leveling says one user, any more opinions? I've gouged out cracks where parts of the leca followed, maybe 3 cm deep in some places. Can I smear in 3 cm of mortar directly, or should I do about 1 cm at a time and let it dry before the next layer?
We will probably use the space down there anyway, even though we are not draining it. It was damp behind the walls and under the floor when the moisture had nowhere to go, but now that everything is torn out, the ventilation we have in the basement seems sufficient to maintain a good climate (RH 50-60% now). Dehumidifier is ready to compensate for the warmest summer days!
I'm worried that I'll use the wrong plaster and everything will fall off the wall since I don't know what it is plastered with today =(
C kc 0-3 mortar in cracks and C kc 0-1 mortar for leveling says one user, any more opinions? I've gouged out cracks where parts of the leca followed, maybe 3 cm deep in some places. Can I smear in 3 cm of mortar directly, or should I do about 1 cm at a time and let it dry before the next layer?
We will probably use the space down there anyway, even though we are not draining it. It was damp behind the walls and under the floor when the moisture had nowhere to go, but now that everything is torn out, the ventilation we have in the basement seems sufficient to maintain a good climate (RH 50-60% now). Dehumidifier is ready to compensate for the warmest summer days!
At least for the small but deep dents, like around removed nails, you should work in stages (when you've chosen your mortar, check the product description for their recommendations). Or use some kind of repair mortar like husfix or ardex a46, but they are very hard and depending on the previous mortar, it may cause cracks when the materials move out of sync. Remember to thoroughly scrape out the dents, for example with a steel brush and then a vacuum cleaner, and pre-wet before applying the mortar.
If the rest of the wall needs to be plastered smooth and it varies as much as a few cm per m, it's probably not a good idea to slap on the finest mortar in a single go; it's usually recommended to keep it under a few mm. I would use a somewhat coarser mortar that, according to the product description, can handle sufficiently thick applications. Alternatively, you could do several rounds of fine mortar, but I find it a bit trickier because you have to get the wall more and more even with each layer, which is difficult when you only have a few mm to work with each time and it's easy to just build on the unevenness. Simplifying the process by just doing a single layer with a bit coarser mortar and using a straightedge and a sanding board could be enough, depending on the surface texture you want?
Regarding the type of plaster, it depends on how precise you want to be. You could knock off a piece and have someone knowledgeable analyze it. Or test different mortars, wait a year (how fun is that?), and then see which gave the best result. Applying a kc-mortar is probably quite safe. Since there hasn't been any paint on it, maybe the surface is full of dirt even if it isn't visible, so clean and pre-wet thoroughly. Worst case, you'll have to knock it down and redo the whole thing.
Remember to wait with the dehumidifier until the mortar has fully cured; in the beginning, it's actually good for it to be damp, otherwise you'll get drying cracks.
If the rest of the wall needs to be plastered smooth and it varies as much as a few cm per m, it's probably not a good idea to slap on the finest mortar in a single go; it's usually recommended to keep it under a few mm. I would use a somewhat coarser mortar that, according to the product description, can handle sufficiently thick applications. Alternatively, you could do several rounds of fine mortar, but I find it a bit trickier because you have to get the wall more and more even with each layer, which is difficult when you only have a few mm to work with each time and it's easy to just build on the unevenness. Simplifying the process by just doing a single layer with a bit coarser mortar and using a straightedge and a sanding board could be enough, depending on the surface texture you want?
Regarding the type of plaster, it depends on how precise you want to be. You could knock off a piece and have someone knowledgeable analyze it. Or test different mortars, wait a year (how fun is that?), and then see which gave the best result. Applying a kc-mortar is probably quite safe. Since there hasn't been any paint on it, maybe the surface is full of dirt even if it isn't visible, so clean and pre-wet thoroughly. Worst case, you'll have to knock it down and redo the whole thing.
Remember to wait with the dehumidifier until the mortar has fully cured; in the beginning, it's actually good for it to be damp, otherwise you'll get drying cracks.
Bumping the thread.
Currently, TS is busy setting up a room in the basement with a new mechanically ventilated floor.
The wallpaper on the walls is in the process of being removed and will be painted later.
Over the years, the wallpaper has been spackled in the corners and against the floor, so not all of it is coming off.
Wallpaper paste is also left behind.
Might rent a giraffe with a dust separator to get a clean plaster surface.
After sanding, you probably need to smooth it out (or can it look okay after sanding???), and a small question is which plaster mix should be used, and also what m2 consumption can be expected when smoothing?
Currently, TS is busy setting up a room in the basement with a new mechanically ventilated floor.
The wallpaper on the walls is in the process of being removed and will be painted later.
Over the years, the wallpaper has been spackled in the corners and against the floor, so not all of it is coming off.
Wallpaper paste is also left behind.
Might rent a giraffe with a dust separator to get a clean plaster surface.
After sanding, you probably need to smooth it out (or can it look okay after sanding???), and a small question is which plaster mix should be used, and also what m2 consumption can be expected when smoothing?