Internal sealing of floor and wall connection

A friendly Grüß Gott to all helpful forum users...

Unfortunately, I have a somewhat special problem (hence the somewhat lengthy text), for which I have not yet found a well-founded/feeling-right solution for implementation. I would greatly appreciate tips from experienced builders/renovators!

Starting situation: Old building from the 60s, not basemented, concrete slab (30cm rubble underneath), exterior walls brick, horizontal barrier typical for the construction year starting from the first row of bricks, completely renovated and expanded, slight slope (north room just above ground level, south side about 1.50m above), occupied by us for 2 years, no other problems

Problem: Earthy smell and moisture since summer 2018 in the north room (there also mold infestation on furniture and clothing, NOT walls) and bathroom, intense after opening the door thresholds

Cause: Wrong sealing compound recommended by a professional friend (PCI Lastogum; for splash water in the shower area, not against penetrating ground moisture), used throughout the entire ground floor ("I've always done it that way; it always worked").

Consequence: Compound on the wall below the horizontal barrier has detached and softened like rubber; floor structure (Fermacell dry screed; also wrongly advised as we now know, since partly organic) moist and infected with bacteria

but:
Lastogum on the floor slab still tight/hard and well bonded with concrete
Problems only occur in north room and bathroom

Plan: Dismantling of the floor in north room and bathroom; proper sealing up to above the horizontal barrier and new floor structure with inorganic material; leaving the floor in the rest of the ground floor as long as no visible problems exist there

Previous information: Several professionals contradict each other in almost every respect (procedure, which rooms, material, floor structure, exact cause, interior or exterior sealing, health hazard...).
Currently, the air quality is good again and moisture is low (due to wintertime/correct ventilation as always/building dryer).

Now my questions, hoping for your help:

- Can the intact Lastogum on the floor slab remain and the new sealing be applied above it, or if not, why must it be milled off?
- What is the best way to realize the wall connection?
- Sealing slurry or bitumen membrane?
- Where vapor barrier or vapor retarder, where not?
- Water-repellent dry screed or must it be flow screed?

Furthermore, a downright creepy piece of information came from one of the professionals:
"There will always be water collecting under the insulation layer and rotting there, basically like a swimming pool" (due to condensation moisture/low dew point on the very cold floor – this issue is now well known to us). But "that does not matter, you wouldn’t notice it."

...If it’s just about not noticing it, one could seal everything airtight and let it rot underneath. That can’t be right??

...If the insulation layer is well glued, no water can accumulate there, but somewhere else in the floor structure where it also evaporates again??

I am looking forward to your tips; many thanks!

Pajero

PS: We know that our approach, not questioning the suitability of the sealing compound, was wrong, but at that time we had no reason to doubt the recommendation of the professional who has advised us excellently elsewhere in the house.

PS: Exterior sealing is planned in the medium term but cannot be carried out before 2025 for several reasons. There are no subjective impairments on walls and in other rooms; the living quality is good, the building fabric (still) not affected.

Dear forum experts,

Doesn't anyone have a tip or advice for us? There are so many related topics here; surely someone can help us? We would be very happy:-)!

Best regards, Pajero

...Many here are very experienced; does really no one have an idea for us? We would be very happy!

Best regards and a Happy New Year, Pajero

I can’t really imagine exactly how the structure is set up there, but I think any internal measure makes no sense without external sealing. Damp walls eventually crumble away. You also can’t apply proper sealing to damp masonry. I don’t necessarily see the wrong sealing compound as the problem here, since it didn’t cause the main issue (moisture from outside). You can only properly address the interior once the problem outside has been fixed. If that can only happen in 5 years (?), then the interior just has to wait that long. Otherwise, you will tear it open again. In the meantime, I would remove the Lastogum and leave the area open so the moisture can dry out.

Would the ceiling height allow for floor insulation to 1. solve the condensation problem and 2. bring the new floor closer to the height of the old moisture barrier between the 1st and 2nd brick layer? ... and thus simplify the connection problem. Otherwise, as Elina writes: dig out and renovate and check whether the old horizontal barrier is still intact.

Hello and many heartfelt thanks for your tips!
The house is from 1962 and the walls have never been sealed from the outside - there were no problems before because the floor construction consisted of inorganic screed on bitumen felt; ergo: the bottom row of bricks has been damp for 57 years and the building fabric is flawless according to the expert report, since the water could not diffuse inward and thus no salts were washed out of the wall. There was also no mold in the room before (and for us only on furniture/carpets etc. and luckily not yet on building components - here the problem is the moisture and odor caused by the resulting colonization).
Unfortunately, we now had a partly organic floor construction with Fermacell dry screed, which could get damp and indeed did so in the area. Only then did the manifest problem with moldy furniture and water diffusing into the floor construction arise (see photos 1, 2 and 3: detached Lastogum and crumbling plaster behind it).

Regarding the height of the floor construction: The polystyrene insulation, dry screed and parquet were together already higher than the old construction (carpet on screed on bitumen felt), so we had to cut the doors.

About "leaving open": It is not just one spot but the entire floor slab and the bottom row of bricks. The floor slab has been sealed with bitumen felt since 1962; although it was no longer intact recently, drying out of the slab has never been an issue because the house is not basemented.
We have largely removed the floor construction today and will soon also remove the wall covering of the bottom row of bricks (plaster on Heraklith) in front of the brick outer wall as well (see photo 3 with the first breakthrough through the wall layers). This area can then dry out; the bricks look like new (see photo 4) - so obviously no damage has occurred here due to the moisture.

An external sealing, unfortunately, is not an option for quite some time - therefore we worry less because as said the situation has left no traces on the building fabric for 57 years.

About the horizontal barrier: It is obviously continuously intact (measurement with the Gann Hydrometer above and below the 1st row of bricks: above between 25 and 30 digits, below 60 and more).
Maybe you can give us a tip whether the horizontal barrier might be damaged when chipping away the Heraklith? It should only be inside the brick wall and therefore no danger should exist?

And since the Lastogum on the floor slab appears to be intact: what do you think of a new floor construction with a cold self-adhesive vapor and radon barrier ON the Lastogum (since it does not adhere anyway on concrete), a vacuum insulation, inorganic screed and then the existing parquet?
(Possibly a bitumen coating and then insulation and screed would be the better variant, since that was obviously fine for a very long time before?)
With the internal plinth sealing we are still uncertain... on the exposed bricks with sealing slurry and vapor barrier raised from the floor? We do not yet know whether a cove fillet is needed and whether a remediation plaster would be necessary or how to proceed after installing the raised vapor barrier.

In any case, we sincerely thank you very much for your interest and your patience and are very happy about your advice :-)!

Best regards,

Pajero