Autoclaved Aerated Concrete blocks as insulator?

murphaph

Hello all,
We have a problem in our Berlin flat. The bedroom has 2 external walls and one (the gable end) gets particularly cold in winter. We have even seen some mould forming though this is preventable when we ventilate the room properly for 10 mins in the morning and is due entirely to room occupation-there is no damp penetrating from the outside etc.

I would like to improve the comfort in the room but am aware that by better insulation the room from the inside (external insulation is not on the cards for the building as the other owners are too tight-hopefully new building regs will force them into it at some stage) will tend to reduce the temp of the outside wall even further and thereby poses a higher risk of damp air condensing on the wall and ultimately forming mould behind any new insulation-something I am determined to avoid.

We took a trip to our equivalent of B&Q to see what they have on offer and spoke to the guy in the building department. He said the best option would be to use Autoclaved Aerated Concrete slabs, bonded directly to the existing block wall (it's very flat and smooth and needs no making good etc.) with thin bead mortar. He said AAC has the property of being able to store moisture from the air and then release it back into the room without becoming damaged (as any normal masonry wall does).

We have a slightly different climate to Ireland with very cold winters. What I like about the method is that there is no vapour barrier to get 100% right and still the thermal properties of the AAC blocks look good (apparently the Swedes build their houses out of them). They cost €10 per m² including mortar and we have 15m² to cover but I think I can get them cheaper elsewhere. The surface would need to be plastered afterwards.

Does anyone have any experience or thoughts about this stuff?

heinbloed

You have the correct material in mind. However the landlord must be asked for permission since the glueing of Ytong or similar is considered to be a permanent solution. It reduces the m2 and the Germans know their rights. They meassure when renting or buying.
The organic matter has to be romoved completely from the inner wall, wall paper, paint, maybe old hair containing plaster (Altbau).
Contact a Baubiologe (a building scientist specialised in mould problems etc.),
you will find them in the "gelbe Seiten" (golden Pages) or here:

http://www.baukammerberlin.de/

If you are renting then talk to the owner, they're usually interested in a good quality of their property. However some sharks (Miethaie) aren't , so contact the Berliner Mieterverein. For a small fee,the anual membership, you'll have free legal advise concerning your apartment.

murphaph

Cheers Hein blöd. We own the flat so thankfully there's no bother on that score. The building is Altbau but our flat was "aufgestockt" (added on top of the existing structure) about 20 years ago. To be honest it's quite disappointing that in a relatively new structure that the insulation is so bad.

Thankfully there is just Raufasertapete (wood chip wallpaper) as is common in Germany on the walls. We wanted to get rid of it anyway. The plastered surface underneath has never been painted so we are sort of lucky that little prep work is required.

I was also looking at Calcium Silicate boards likethese but they are horrendously expensive in comparison (starting at €30 per m²) so the suggestion from the OBI guy is interesting to us.

Nochmal, vielen Dank

heinbloed

I think the (Greek-) my-value is decisive for the choice of material, not the brand. This my-value has to be considered up through the entire build-up, each layer, including the final layer to the room side(wall paper, paint).
Obi offers DIY courses, Steglitz has some good choice:

http://www.obi.de/de/markets/maerkte/Berlin-Steglitz/events/index.html

In 5 hours you'll know more than most builders in Ireland about a particular issue. Be it internal or external insulation, tiling or plumbing.
Talk to your shop floor staff, they'll organise a course if enough interest is there.
Get a certificate in writing from the course organiser and you can register with the NSAI as a professional-if coming back (smiley).

PS
Here some literature, note the first link:
http://www.tzwl.de/downloadbereich/schimmel_in_innenraeumen