Builder wants to mist coat before tiling & fitting bathroom!!

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Hi - just wondered if I could get seem advice on when to mist coat fresh plaster, and whether I then need to top coat quite soon after or not, please??

My builder is suggesting I mist coat our newly built, and newly plastered, bathrooms before he starts to tile and install the bathroom fittings, because it can be such a messy job. Meanwhile the rest of the house is also being plastered, and the weather outside is pretty cold and damp, so I imagine the plaster is going to take longer than normal to dry, especially as we have no heating in the house at the moment.

Are we okay to mist coat before the plaster is potentially fully dried out, and then do the top coats at a later date, once the bathrooms have been installed? Or would we be better to just wait and do the whole paint job later on, properly covering everything up, when we can be sure the plaster is fully dried out?

Thanks!
 
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I aint going to call this as knowledge but just logic. If you do a mist coat the idea is that the paint is thin enough that it penetrates the plaster and doesn't dry to quick and peel off. So to do a mist coat on not quite dry plaster I can't imagine is an issue but I would be interested in other opinion with supporting arguments though,
 
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Ideally the plaster should be dry, but if you have to mist coat before then make sure you use contract emulsion as it contains no vinyl and will allow the plaster to breathe. If you use vinyl emulsion to mist coat plaster that's not fully dry it may fail and blister. After mist coating with the contract emulsion, leave the plaster to then fully dry before applying any emulsion of your choice.
 
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Thanks so much for your responses, Jadele and ic1927 - am i okay to do the top coat a few weeks after the mist coat, once the bathroom has been fitted then, or should the misting and top coats be done quite close together in time? It sounds as if I should definitely not rush and do the top coats when there's still a chance that the plaster underneath might be slightly damp, but a mist coat might be all right? I have suffered with paint peeling off in strips right back to the bare plaster before, and there's no way I want that to happen again! Such a horrible messy job. But if I can mist earlier, using the correct matt emulsion, without causing a problem, then at least I'd be able to get a very messy job out of the way before all the new bathroom fittings go in - or would you just wait and do it all afterwards? My builder seems keen to at least mist coat now, as he says it seals the plaster, and will stop mould patches from forming (which seems to be happening in some of the rooms). Thanks again!
 
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you shouldn't be getting mould patches on new plaster, if you are and it is taking this long to dry then get some windows open and some heat into the rooms.
Has it been plastered over plasterboard or backing plaster.
Personally I would let it dry out properly won't take more than a day or two either way. Mist coat and paint to within one coat of finished, then fit the bathroom.
 
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Apparently the new plaster is mostly onto plasterboard, apart from in some places where just a patch up was required. Why, does it make a difference to the drying times? We live on the coast, so it's a pretty damp location. But the house has just been renovated to try to eliminate the damp problems we were experiencing on some of the walls, so I'm hoping this mould on the new plaster is not a sign that we are still going to have issues?? The builders do seem to be leaving the windows open whilst they are working, but at night time, they are closed up as it can get pretty windy here! There's no central heating on in the house, as the plumbing work is still ongoing, but they have a heater that they are using during the daytime. You've got me worried now that the mould is not a good thing - my builder tried to brush it off as normal when there's so much moisture in the air!?
 
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You may always have a problem with mould growing on a cold external wall as that's where the most moisture will gather, but once the central heating is back up and running and sufficient ventilation then this should make a difference (won't say eliminate), have a look at anti mould paints if it is a big problem.
Make sure to give the mould a wash off with diluted bleach first before painting.
 
D

Doggit

If they've plastered over plasterboard, then it'll dry in a few days, but when there's backing plaster behind it, then that has to dry as well, so could well take a week, but mould takes longer to form, so you've got other issues elsewhere to get that. You want to do a mist 50/50 paint and water before you start fitting the bathroom, as it'll splatter everywhere, but are they suggesting you do the mist coat where they're going to tile, as that's a no no. You don't need to mist and then paint straight away, and can leave it as long as you like to paint the top coat, just wipe it down to remove any dust that may have accumulated if you leave it for too long. A dehumidifier is much better at drying out plaster than heating is, as too much heating can crack the plaster (unlikely but it does happen) and the heating will just put the moisture into the air after which it's got to go somewhere. As others have suggested consider using ant mould paint in the bathroom,

The mist coat seals the dust into the plaster, but won't stop mould forming, as that's caused by moisture on a cold wall, so careful of what they are telling you. Have any of the walls been insulated, or is this just a general renovation job.
 
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If you are getting mould forming on fresh plaster before it has dried or even soon after then you have more fundamental issues to deal with and shouldn't yet be painting anyway.
 
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Thanks guys - you've all been really helpful.

Sounds like I need to take a closer look at why we are getting mould on these walls. Any new walls in the house have been insulated, but the rooms where the mould is happening, all have external old stone walls, that have no insulation, but have just been "tanked" in order to to seal them properly from the damp.

Good to hear that mist coating won't protect the walls from mould, as this didn't sound right to me at all! And nice to know that we can mist coat, and then it doesn't matter how long it then takes to getting around to painting the top coat. Means that we should be able to at least mist the rooms where we don't have any mould growing. Will definitely get mould resistant paint for the bathrooms.

Thank you so much! Really good to hear all your advise and wise words. Such a helpful site - and really appreciate the time you've taken out of your day to help me.
 
D

Doggit

I'd kick the builders off site having just heard they've tanked the stone walls to protect them from the damp. Stone walls work differently to brick, so shouldn't be tanked. They'd have been better off erecting a stud wall with insulation and a vapour control barrier. It's the cold stone walls that are causing the mould.

The real trick to getting rid of mould, is to keep the rooms well ventilated, and well heated.
 
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Yikes! We'd have lost a lot of internal space if they'd gone down the stud wall route. Its only a few rooms that had to have their one external wall tanked, and it looked as if it was our one and only real option to protect us from the prevailing weather. They spent a lot of time repointing the house with lime outside, so that the dampness should now be allowed to dry out a bit better. I really hope the tanking isn't just going to cause us a whole heap of new problems going forward now....
Thanks for your help, Doggit - hopefully things will get better once we can move back in and get the heating on and the windows opened...
 
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Doggit

You could have got a way with about 4" per wall, and if you find the problem still exists, come back and chat again. Beyond that, best of luck.
 
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Back to the painting issue, don't paint/mist the wall where the bathroom guy will be tiling.....he doesn't want to be tiling onto a painted surface.
 

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