Hello!
I have now (hopefully) completed the plastering of old basement walls (brick house from 1900, likely built with lime mortar or similar). Some are exterior, some interior walls - and now I'm starting to worry that they won't dry... The drying time of these walls varies considerably; some exterior walls are drying as planned and the plaster has assumed a dry/set/hardened state, others are still somewhat cold/damp, though hard, but if you rub slightly on the "damp spots," you can feel that they are not fully dry. Even some interior walls, like parts of the partition wall, still have this "dilemma."
I suspect not surprisingly that these have higher moisture content, but... Is it just a matter of waiting and seeing, or should I accelerate the drying time by heating the space? What risks are there if the drying takes too long? Can you even dare to paint these walls - with silicate paint - if they (once they are finally dry) still likely contain moisture!?
I have now (hopefully) completed the plastering of old basement walls (brick house from 1900, likely built with lime mortar or similar). Some are exterior, some interior walls - and now I'm starting to worry that they won't dry... The drying time of these walls varies considerably; some exterior walls are drying as planned and the plaster has assumed a dry/set/hardened state, others are still somewhat cold/damp, though hard, but if you rub slightly on the "damp spots," you can feel that they are not fully dry. Even some interior walls, like parts of the partition wall, still have this "dilemma."
I suspect not surprisingly that these have higher moisture content, but... Is it just a matter of waiting and seeing, or should I accelerate the drying time by heating the space? What risks are there if the drying takes too long? Can you even dare to paint these walls - with silicate paint - if they (once they are finally dry) still likely contain moisture!?
Not to sound whiny, but many do not recommend gypsum plaster on basement walls because it is too dense and does not withstand constant moisture migration, regular plaster usually works better in damp basements.
if there is a non-functioning drainage, the basement walls will be constantly moisture-laden so they do not dry out.
is the house drained and has the basement been dry before you started plastering?
if there is a non-functioning drainage, the basement walls will be constantly moisture-laden so they do not dry out.
is the house drained and has the basement been dry before you started plastering?
Hmmm, would be pretty typical in that case... Yes, the house is drained, so on that outer wall, it's ok, patchily darker but otherwise quite ok. In that regard, one can probably conclude that it has been relatively dry. I read somewhere here that gypsum plaster was most suitable when there was mortar behind it - although not if there was a risk of moisture migration - but the wall that seems hardest to get dry is an interior wall (the heart wall)! Do you recommend pressing on with a heater to speed up the drying?
I use some gypsum plaster on the interior walls at home to achieve a plastered look. Now it's on the entrance level and never directly on the exterior walls, so it differs a bit from your use of the material!
What I can say, though, is that it takes a shockingly (relatively) long time to dry. I apply about 5 mm of gypsum plaster on the walls (with plasterboard behind) and it's a normal indoor temperature in the room (around 19-21 degrees). I initially thought it would dry in a few hours considering the thin application. But now I know it takes at least 3 days before it's dry and can be painted... The day after, you can see how it's dried in some places and still damp in others. Where it's thickest, usually in the inner corners, you should count on about 3 days before it's done...
So on a cold basement wall with moisture, I think it could take significantly longer...
I use MP75L from Knauf. I tried using a dehumidifier in one room to see if it made a difference, but it was negligible. I haven't tried a heater but imagine it might crack then?
What I can say, though, is that it takes a shockingly (relatively) long time to dry. I apply about 5 mm of gypsum plaster on the walls (with plasterboard behind) and it's a normal indoor temperature in the room (around 19-21 degrees). I initially thought it would dry in a few hours considering the thin application. But now I know it takes at least 3 days before it's dry and can be painted... The day after, you can see how it's dried in some places and still damp in others. Where it's thickest, usually in the inner corners, you should count on about 3 days before it's done...
So on a cold basement wall with moisture, I think it could take significantly longer...
I use MP75L from Knauf. I tried using a dehumidifier in one room to see if it made a difference, but it was negligible. I haven't tried a heater but imagine it might crack then?
Interesting, the thickness of my walls varies quite a bit from 5 mm to 3-4 cm, but my walls have dried in very different amounts of time, regardless of thickness. I used two different types of plaster, Norgips (K-rauta) and another one I can't remember the name of, bought from Jem&Fix (similar in price) - so that might have something to do with the difference in drying time. But not to this extent, I think. Norgips is the one causing the most trouble - it's been almost a week and it's still not completely dry, whether it's an outer or inner wall - I'm going to kick K-rauta in the shins if they've recommended the wrong type... ) I've put down a dehumidifier, at least it can't make it worse, raises the temperature and dries out. I'm holding off on the heater - most worried about whether this long drying time affects the strength and if the stuff will come off after a while...
Gypsum plaster is a good material for interior walls but not risk-free in an old basement. It tolerates moisture movement as little as a drywall. Even if the house is drained, there is often some moisture movement along the floor in old houses, and it's so sad to see new damages coming after all the work one has put in. It's too late for changes in TS's case, but maybe others will read and have time to consider their material choices.meckis said:
I get so angry at all the sellers who sell the wrong material and avoid all responsibility if it goes wrong. I've personally removed a lot of disintegrated wall coatings in my basement made with materials considered "best" at the time - cement, gypsum filler, some plastic filler ... whatever the seller had on the shelf. Lime plaster, which was most suitable for an old basement, was forgotten in a storage corner. It's now been about 7 years after replastering with lime plaster, and the walls look and feel dry despite the little moisture movement that constantly occurs in my basement (ground moisture is drawn up capillarily). No other building material can handle moderate moisture movement as well as lime plaster does, so it should be the first choice when plastering an old basement that was originally plastered with lime plaster. Choosing otherwise just goes wrong.
gaia