Hello,
I have a problem with the floor in my "new" house from 1953.
The floor is about 20 mm (0.8 inches) lower than the hallway. Previously, there was 10 mm (0.4 inches) of glued polystyrene foam and high-pile carpet. Below that is an unheated basement, and it felt quite warm underfoot!
The other rooms have some kind of screed with a wood fiber board(?).
I’ve never seen this before. Therefore, I assume that in my bedroom there is no insulation or screed at all, just a concrete ceiling.
The hallway will be tiled over, so it will get a bit higher, around 30 mm (1.2 inches)?
QUESTION: Can I glue 20 mm (0.8 inches) XPS 300 rigid foam board and pour 10 mm (0.4 inches) of leveling compound?
Possibly with reinforcing mesh. Will this work?
Best regards,
Olaf R.
I have a problem with the floor in my "new" house from 1953.
The floor is about 20 mm (0.8 inches) lower than the hallway. Previously, there was 10 mm (0.4 inches) of glued polystyrene foam and high-pile carpet. Below that is an unheated basement, and it felt quite warm underfoot!
The other rooms have some kind of screed with a wood fiber board(?).
I’ve never seen this before. Therefore, I assume that in my bedroom there is no insulation or screed at all, just a concrete ceiling.
The hallway will be tiled over, so it will get a bit higher, around 30 mm (1.2 inches)?
QUESTION: Can I glue 20 mm (0.8 inches) XPS 300 rigid foam board and pour 10 mm (0.4 inches) of leveling compound?
Possibly with reinforcing mesh. Will this work?
Best regards,
Olaf R.
Hello Olaf,
As a general note at this point: Insulation should be installed on the underside of the ceiling in the basement! That is where it belongs, always on the cold side.
The insulation boards you mentioned are not suitable as a substrate for floor coverings. Therefore, drop the idea of gluing anything onto them.
If the floor surface is now 20mm (0.8 inches) lower after removing the old construction, this only causes issues at construction joints—meaning at stair landings or room transitions where the floor height might be higher.
Do it like this:
First, thoroughly sand the substrate exposed after removing the old insulation and textile covering (concrete? old screed?), then carefully vacuum the dust from the surface.
Next, prime the entire surface (an emulsion primer is perfectly sufficient) and level the visible substrate surface with about 3mm (0.1 inches) of filler. This creates a smooth, installation-ready surface for later bonding of the floor covering.
At transitions to other rooms that still have their original height (i.e., higher floors), ramp-shaped smoothing should be applied using a sturdy filler.
The approximate ramp length can be calculated with the formula:
> cm height difference x 0.6 = ramp length in meters <
For a 3cm (1.2 inches) height difference, this would be about 1.8m (5.9 feet) of ramp length extending into the room.
This dimension ensures no tripping hazard occurs.
Within the room itself, it doesn’t matter whether the subfloor is 3cm (1.2 inches) higher or lower than in the adjacent room.
But it’s best to avoid considering insulation boards as an indirectly usable surface under a floor covering!
-------------------
I would leave the wood chipboard substrate in place if it is still load-bearing and does not show any bending when walked on.
Only the insulation in the basement is important for maintaining comfortable floor temperatures, and this should be ensured by the next flooring layer.
Wishing you success: KlaRa
As a general note at this point: Insulation should be installed on the underside of the ceiling in the basement! That is where it belongs, always on the cold side.
The insulation boards you mentioned are not suitable as a substrate for floor coverings. Therefore, drop the idea of gluing anything onto them.
If the floor surface is now 20mm (0.8 inches) lower after removing the old construction, this only causes issues at construction joints—meaning at stair landings or room transitions where the floor height might be higher.
Do it like this:
First, thoroughly sand the substrate exposed after removing the old insulation and textile covering (concrete? old screed?), then carefully vacuum the dust from the surface.
Next, prime the entire surface (an emulsion primer is perfectly sufficient) and level the visible substrate surface with about 3mm (0.1 inches) of filler. This creates a smooth, installation-ready surface for later bonding of the floor covering.
At transitions to other rooms that still have their original height (i.e., higher floors), ramp-shaped smoothing should be applied using a sturdy filler.
The approximate ramp length can be calculated with the formula:
> cm height difference x 0.6 = ramp length in meters <
For a 3cm (1.2 inches) height difference, this would be about 1.8m (5.9 feet) of ramp length extending into the room.
This dimension ensures no tripping hazard occurs.
Within the room itself, it doesn’t matter whether the subfloor is 3cm (1.2 inches) higher or lower than in the adjacent room.
But it’s best to avoid considering insulation boards as an indirectly usable surface under a floor covering!
-------------------
I would leave the wood chipboard substrate in place if it is still load-bearing and does not show any bending when walked on.
Only the insulation in the basement is important for maintaining comfortable floor temperatures, and this should be ensured by the next flooring layer.
Wishing you success: KlaRa
Thank you for your response.
I’m not really satisfied with the solution, so I will probably pour 3–3.5cm (1.2–1.4 inches) of self-leveling screed—FE50-Largo.
Now, a basic question: Since I am pouring screed onto concrete (old leveling compound), do I need to install a separating layer (plastic sheet)? Currently, I have edge strips and a layer of acrylic primer (EcoPrimT PLUS) applied. It feels rubbery!
Is that okay?
I’m not really satisfied with the solution, so I will probably pour 3–3.5cm (1.2–1.4 inches) of self-leveling screed—FE50-Largo.
Now, a basic question: Since I am pouring screed onto concrete (old leveling compound), do I need to install a separating layer (plastic sheet)? Currently, I have edge strips and a layer of acrylic primer (EcoPrimT PLUS) applied. It feels rubbery!
Is that okay?
@Olaf R.:
Apparently, you didn’t read my answer (properly).
No one suggested pouring 3–3.5cm (1.2–1.4 inches) of leveling compound somewhere.
I was referring to applying a standard self-leveling underlayment (which not only evens out the existing screed surface but also provides a stable substrate for subsequent adhesives) and smoothing the transitions.
A membrane is neither practical nor possible because—according to DIN 18560 Part 4—for uncoupling screeds in residential construction a minimum thickness of approximately 45mm (1.8 inches) of cement screed is required.
What good would a membrane do under a 3–3.5mm (0.12–0.14 inch) thick layer of leveling compound except crumble the moment it is walked on?
Edge insulation strips must be installed between unheated screeds and wall surfaces, with a thickness of 5–8mm (0.2–0.3 inches), for soundproofing reasons.
Conclusion:
Anyone experimenting with any compound without the necessary background knowledge about why certain steps are required should not be surprised when the result does not meet expectations.
Of course, the choice is yours. But you should not ignore the warnings from those who have been professionally involved in the field of “flooring technology” for decades…….
----------------
Still: good luck: KlaRa
Apparently, you didn’t read my answer (properly).
No one suggested pouring 3–3.5cm (1.2–1.4 inches) of leveling compound somewhere.
I was referring to applying a standard self-leveling underlayment (which not only evens out the existing screed surface but also provides a stable substrate for subsequent adhesives) and smoothing the transitions.
A membrane is neither practical nor possible because—according to DIN 18560 Part 4—for uncoupling screeds in residential construction a minimum thickness of approximately 45mm (1.8 inches) of cement screed is required.
What good would a membrane do under a 3–3.5mm (0.12–0.14 inch) thick layer of leveling compound except crumble the moment it is walked on?
Edge insulation strips must be installed between unheated screeds and wall surfaces, with a thickness of 5–8mm (0.2–0.3 inches), for soundproofing reasons.
Conclusion:
Anyone experimenting with any compound without the necessary background knowledge about why certain steps are required should not be surprised when the result does not meet expectations.
Of course, the choice is yours. But you should not ignore the warnings from those who have been professionally involved in the field of “flooring technology” for decades…….
----------------
Still: good luck: KlaRa
Ok, but you mentioned "applying about 3mm (0.1 inch) of filler to the visible surface of the substrate" and "at the transitions to other rooms… (which are higher) ramps are formed with a stable filler compound."
I don’t want that.
Otherwise, I would be at least 3–3.5cm (1.2–1.4 inches) lower than the finished floor level in the other rooms, and the floor wouldn’t be level at the transitions.
Currently, the room only has the reinforced concrete with a firm layer of leveling compound.
Therefore, I will now use flowing screed. It can be applied from a layer thickness of 30mm (1.2 inches). That is perfect. According to Knauf’s instructions, it can be done with or without a membrane. As far as I know, you only use a membrane if there is thermal and/or impact sound insulation underneath. I don’t have that.
I will do this together with my drywall installer, who is a trained bricklayer. Thanks!
I don’t want that.
Otherwise, I would be at least 3–3.5cm (1.2–1.4 inches) lower than the finished floor level in the other rooms, and the floor wouldn’t be level at the transitions.
Currently, the room only has the reinforced concrete with a firm layer of leveling compound.
Therefore, I will now use flowing screed. It can be applied from a layer thickness of 30mm (1.2 inches). That is perfect. According to Knauf’s instructions, it can be done with or without a membrane. As far as I know, you only use a membrane if there is thermal and/or impact sound insulation underneath. I don’t have that.
I will do this together with my drywall installer, who is a trained bricklayer. Thanks!
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