Hello.
Split-level house built in '67. Due to an old water damage (caused by inadequate drainage in '67), my newly purchased recreational room has been left untouched. It's a story in itself, but there was water damage, the drainage was redone, but nothing was done in the recreational room when one of the owners suddenly passed away. Now I don't feel any moisture at all, it seems calm.
So now I've taken over and removed everything.
The plaster was quite loose in many places as expected, so I've knocked off all the loose parts.
There is blåbetong behind, as you can see in the pictures below. What should I do with the wall now? I want to plaster, but with what should I plaster? Is there something more suitable for radon? I've heard good things about gypsum and it sounds fun, but is it suitable, considering there were some deep holes?
The radon level is at 400 now, so not a disaster but above the limit, I'm thinking of supplementing the natural ventilation with some mechanical exhaust and using ventilated flooring in the recreational room.
Gypsum may be fun and certainly handles holes quite well, but strictly according to the rulebook, gypsum plaster below ground is not recommended. Even if drainage is now arranged and you're not noticing any additional moisture. If you use the search function, you'll see similar threads where some people go for it anyway, but you should be aware that a cement-based product is probably what should be used. Unfortunately, it's a jungle which plaster is suitable for lättbetong though.
That said, I have personally used gypsum plaster on lättbetong, both above and below ground, and find it wonderfully easy to work with compared to cement-based products.
