Fresh plaster slightly patchy but also cracking

[randomdave]

Had our front bedroom replastered (all walls and ceiling) more than 2 weeks ago and was told it'd be fine to paint a "mist coat" of watered down emulsion after a few days (one week max). We left it a little longer as there were still a couple of very slightly darker areas above the windows but there are also cracks beginning to appear on the really dry areas. I had left it totally alone for the first week (with the windows open whenever we were in the house) and for the last week its had a heater on in there at night as well to try and speed the process along.

Everything was perfectly dry to the touch and I didn't want the cracked areas to become too dry without being sealed so yesterday I applied a mist coat to the whole room. This morning, most of the walls look really nice but the patches above the windows are still quite dark. There's also one other patch which had previously looked perfectly dry before we painted it but has gone dark as well.

First question is have I made a massive mistake in painting a mist coat onto areas that perhaps aren't 100% dry? If so, what can I expect the result to be and is there anything I can now do to minimise problems? Or am I just panicing?

Second question is what to do next? Should I now leave the room until its all gone totally dry? How long should I expect that to take (its all been dry for over a week - its just those patches and they don't seem to have been getting drier!)? And then should I do a second mist coat or is it ok just to go ahead and decorate?

Thanks in advance for any help and advice.

 

[PrenticeBoyofDerry]

First question is have I made a massive mistake in painting a mist coat onto areas that perhaps aren't 100% dry? If so, what can I expect the result to be and is there anything I can now do to minimise problems? Or am I just panicing?

During the curing stages plaster can go through cycles of differing colour shading even sometime return to a darker shade.
I personally would not apply paint to plastered walls until completely dry, it can sometimes take upto 2 months for the drying process to be complete.
You have done what you have done and for the moment I would stand down and let the plaster dry and where cracks have occurred I would contact the plasterer regarding this, as it sounds like the area has not been prepared sufficiently.

Second question is what to do next? Should I now leave the room until its all gone totally dry? How long should I expect that to take (its all been dry for over a week - its just those patches and they don't seem to have been getting drier!)? And then should I do a second mist coat or is it ok just to go ahead and decorate?

I think most of these points have been covered above, simple answer is give the plaster a reasonable time to dry/cure prior to priming for painting, the drying period is not an exact sciences and depth of coats, condition of wall, weather conditions and environmental temperatures can all factor into this.

 

[randomdave]

Thanks very much for the quick reply.

Do you (or anyone else) have any idea what the results of painting the mist coat too early might be? Will it just take longer to dry or have I totally ruined the new plaster and will need to get the plasterers to start again?! Perhaps there's someone out there who understands the mechanics of the materials a little better than me.

I've now got all the upstairs windows wide open (luckily its a nice day!) and a heater keeping the room nice and warm

 

[loply]

What ratio was your mist coat, and what type and brand of paint?

Generally when I've pushed my luck and painted too early the paint ends up not bonded to the wall and either bubbles off in large blisters or cracks and flakes off.

A lot will depend on how watery your mist coat was.

 

[randomdave]

Thanks for the reply. The mist coat was roughly half paint and half water. We just used cheap (B&Q own brand) white, matt emulsion. Apparently it has a low VOC content (whatever that is!).

So do you feel its unlikely that the plaster will have been damaged then? I can deal with paint bobbling and pealing off - that's easy to redo! Thanks.

 

[Micilin]

It's unlikely that a water based paint , diluted with water, will cause any problem on plaster that is a week old, unless the plaster was still wet to the touch. Problems are with vinyl type paints etcthat are not permeable to water.

 

[randomdave]

Thank you for that. Takes a little weight off my mind! Very much appreciate all the help.