ᐅ Insulating an Unprotected Basement Wall with Bitumen After Construction?
Created on: 3 Oct 2017 00:18
A
Andy70Hello,
I have a single-family house (built in 2001, which I bought from the previous owner in 2006) and have had damp basement walls for years, worsening over time, now with mold growth on the walls. Apparently, only the walls facing the garden outside are too damp. This was confirmed by a building biologist’s measurement. The other basement walls are enclosed by the garage, terrace, and front stairs, etc. But some of these walls are also slightly damp, especially near the floor, though not severely.
Today, I dug up a small section of the exterior wall down to the foundation slab and saw that the bitumen coating is only present in the upper area (about 30-35cm (12-14 inches)). Below that, down to the foundation slab, everything is unprotected (!). You can basically see the bare masonry bricks which were only plastered. No wonder the walls have been damp for 16 years (room humidity often 83%). At least there is a cove fillet (fillet molding at the base). We will excavate the entire area this weekend (with an excavator) and a friend plans to seal it later with a 4-5mm (0.15-0.2 inch) thick bitumen membrane and dimpled drainage sheets.
I have three questions about this:
1) How long should the walls be allowed to dry out from the outside after the surrounding soil is removed before applying the bitumen coating? Of course, in the meantime it will be protected from rain with a tarp. Is 3-4 weeks enough? A dehumidifier (capacity: 20 liters/24 hours) has been running inside since today.
2) Does the existing cove fillet need to be removed and rebuilt, or can it be used as is and simply coated with bitumen? I’m not really an expert and am unsure whether the cove fillet might have suffered damage over 16 years of wet soil contact and become porous. Or is a bitumen coating sufficient if it feels solid and looks apparently “good”? At the one spot we dug, it looks fine from a distance. We will only know more when the whole section is excavated this weekend. My main question is whether it is absolutely necessary to replace it because it was unprotected for so many years, or if that is not essential. A bricklayer friend (a bit removed) said it should not be a problem: just clean it, apply bitumen, and that’s it. Is that correct?
3) The building biologist and a renovation company told me that the two walls which are not built against anything on the outside are the main culprits. The other walls seem to have become damp over the years from the water that seeps in there. That is why these are slightly damp as well. Using a dehumidifier, I should be able to gradually dry out the rooms. The dehumidifier has been running since today. Is it plausible that the moisture from those two affected walls has spread across half the basement over the years? The humidity in the other basement rooms is also high (above 75% and sometimes over 80%).
Thanks in advance for your advice.
Best regards
Andy
I have a single-family house (built in 2001, which I bought from the previous owner in 2006) and have had damp basement walls for years, worsening over time, now with mold growth on the walls. Apparently, only the walls facing the garden outside are too damp. This was confirmed by a building biologist’s measurement. The other basement walls are enclosed by the garage, terrace, and front stairs, etc. But some of these walls are also slightly damp, especially near the floor, though not severely.
Today, I dug up a small section of the exterior wall down to the foundation slab and saw that the bitumen coating is only present in the upper area (about 30-35cm (12-14 inches)). Below that, down to the foundation slab, everything is unprotected (!). You can basically see the bare masonry bricks which were only plastered. No wonder the walls have been damp for 16 years (room humidity often 83%). At least there is a cove fillet (fillet molding at the base). We will excavate the entire area this weekend (with an excavator) and a friend plans to seal it later with a 4-5mm (0.15-0.2 inch) thick bitumen membrane and dimpled drainage sheets.
I have three questions about this:
1) How long should the walls be allowed to dry out from the outside after the surrounding soil is removed before applying the bitumen coating? Of course, in the meantime it will be protected from rain with a tarp. Is 3-4 weeks enough? A dehumidifier (capacity: 20 liters/24 hours) has been running inside since today.
2) Does the existing cove fillet need to be removed and rebuilt, or can it be used as is and simply coated with bitumen? I’m not really an expert and am unsure whether the cove fillet might have suffered damage over 16 years of wet soil contact and become porous. Or is a bitumen coating sufficient if it feels solid and looks apparently “good”? At the one spot we dug, it looks fine from a distance. We will only know more when the whole section is excavated this weekend. My main question is whether it is absolutely necessary to replace it because it was unprotected for so many years, or if that is not essential. A bricklayer friend (a bit removed) said it should not be a problem: just clean it, apply bitumen, and that’s it. Is that correct?
3) The building biologist and a renovation company told me that the two walls which are not built against anything on the outside are the main culprits. The other walls seem to have become damp over the years from the water that seeps in there. That is why these are slightly damp as well. Using a dehumidifier, I should be able to gradually dry out the rooms. The dehumidifier has been running since today. Is it plausible that the moisture from those two affected walls has spread across half the basement over the years? The humidity in the other basement rooms is also high (above 75% and sometimes over 80%).
Thanks in advance for your advice.
Best regards
Andy
Hello Andy, years ago we had a similar problem—excavate, dry, install a new cove fillet, apply bitumen coating twice, add perimeter insulation, and a dimpled membrane—plus a drainage pipe 20cm (8 inches) below the footing with a 30cm (12 inches) concrete chamber and a sewage pump. (The pump ran about three times a year) ;(with the pump, you can also reach walls you can’t excavate). After three weeks, you can probably apply the coating; the rest will dry out internally anyway. Regards, Dietema
Hello,
thanks for the information.
The whole situation has changed fundamentally by now. We excavated earlier today and had a mason come over. I have a waterproof concrete tank (white tanking), so there is no bitumen coating or fillet mortar. Only at the transition to the masonry, the exterior was sealed with bitumen for 40-50 cm (16-20 inches). This seems to be perforated, which is probably why the walls got damp....
thanks for the information.
The whole situation has changed fundamentally by now. We excavated earlier today and had a mason come over. I have a waterproof concrete tank (white tanking), so there is no bitumen coating or fillet mortar. Only at the transition to the masonry, the exterior was sealed with bitumen for 40-50 cm (16-20 inches). This seems to be perforated, which is probably why the walls got damp....
Andy70 schrieb:
Hello,
thanks for the information.
The situation has fundamentally changed by now. We excavated earlier today and had a mason come over. I have a waterproof concrete tank (white tank method), and there is no bitumen coating or fillet mortar. Only at the junction to the masonry, about 40-50cm (15-20 inches) from the outside, was bitumen applied as a sealant. This area seems to be perforated, which is probably why the walls have become damp... Could a white tank also be leaking (due to incorrect concrete mix, poor workmanship, etc.)?
Hello Andy, then the question arises, as mentioned above, whether the connection between the floor slab and the concrete wall is really airtight, or if the moisture problem is caused by condensation – concrete is cold and gets damp first – so definitely insulate! (Has anyone ever said where the dew point is located?) Regards,
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