Help-peeling paint

[hm1986]

Hi, I'm currently redoing our bathroom, and have had all the walls replastered(rendered then skimmed), and have now started painting.The walls have been left for approx 2 months to dry out and now appear totaly dry, and I have coated them with a diluted coat of mat emulsion, which appeared to take fine. Now i have got to the topcoat stage, but having put on 1 coat of Dulux bathroom paint, it is now starting to crack and peel in patches? Any help or advice would be much appreciated.

 

[xr4x4]

are these areas subject to heat?

ie near radiators, or hot air vents.

 

[Richard C]

How much did you dilute the mist coats? How many coats did you put on? What did the plaster look like before you painted it, was it highly polished & nice & shiny?

 

[hm1986]

the cracks that appeared were not near any areas of real heat, other end of the room from the radiator. I probably diluted the paint about 3 parts paint to 1 part water, gave it t2 coats before puting on the top coat.Wouyld say the plaster was polished, more dull but felt very dry to touch, leaving dust marks on your hands etc. Have now sanded off a small patch of the problem paint, and think that the wall now feels cold and slightly damp to touch in comparison to how it felt before I painted it.

 

[Richard C]

Have now sanded off a small patch of the problem paint, and think that the wall now feels cold and slightly damp to touch in comparison to how it felt before I painted it.

Did you have any issue with damp, is that why the walls were re-rendered? What sort of walls are they, solid or cavity?

Just to be clear, is it just the paint that’s cracking or is the plaster cracking as well?

 

[hm1986]

hi no there were no issues with damp in thr room-it was re-rendered due to old render droping off when new windows were fitted and generally not being vrery straight.the walls are cavity walls, and it is just the paint which has cracked.

 

[Richard C]

It may be there was still some residual moisture in the plaster; a base & top coat will usually be OK after 4 weeks but as yours was left for 2 months, I would not have expected any problems. Is the bathroom paint peeling away from the mist coats or is it pulling the mist coat off the plaster with it? Is the peeling general or in patches in specific areas; i.e. next to or underneath windows?

You don’t seem to have made any obvious mistakes so far & I’m at a bit of a loss to guess what’s happened unless there is damp in there.

 

[hm1986]

well where i have scraped the peeling patches the mist coat has come away also, but it doesnt seem to be peeling everywhere just relatively small random patches?

 

[Nige F]

PVA migration through the plaster ..it`s all stable now but those patches are where it is . I`d use a zinsser sealer over them

 

[hm1986]

thanks for your replies, but this isnt really working-having now decided to sand off all the paint back to the bare plaster and start again. I coated the walls with diluted dulux supermatt emulsion (2 coats), which appeared to take fine, and the applied a top coat of a water based emulsion paint within 24hours is has cracked all over again, taking the mist coat along with it. I am now 99% certain that the plaster is fully dried out, so can only assume that there is some sort of chemical reaction occuring between the paint and the plaster. I know that pva was used in the plastering process, is this @pva migration@ as you call it responsible? any nsuggestions would be appreciated.

 

[Richard C]

Hello,

Since bathrooms are typically a bit more confined than most other rooms within the home and are frequently wet from shower and bathtub use, there are a few certain decorating needs that must be met. One need that must be addressed when redecorating a bathroom is using the correct kinds of paint. Due to the high-moisture content in bathrooms, this isn't a case where just any can of paint will do.
Bathrooms require a coat of water-based primer before painting the walls with your chosen color. This primer helps seal moisture away from the drywall, which could lead to serious problems with mildew. Some bathroom walls and/or ceilings have become so saturated with mildew that the drywall had to come down and in severe cases some of the studs required replacing.
Follow the coat of moisture-resistant primer with mildew-resistant paint. In some bathrooms that lack proper ventilation, mildew becomes visible on a weekly basis. While mildew-resistant paint won't completely prevent all instances of mildew from occurring, it will prevent it from occurring as often, and it won't allow it to penetrate as deeply, thus preserving the integrity of the actual wall.
if your bathroom has a serious moisture problem, using a paint with a semi-gloss finish (provided it is mildew resistant) will make routine cleaning a much easier process. The smooth finish of the semi-gloss paint wipes up easily with a damp sponge, yet is strong enough not to be marred by many bathroom cleaning products.

thanks!!

_________________
twin size comforter

Firstly this post is not about dry wall so you've got that completely wrong; secondly you are using your post as a crude link to advertising bed linen products which really doesn’t help with the OP’s problem.

 

[Richard C]

thanks for your replies, but this isnt really working-having now decided to sand off all the paint back to the bare plaster and start again. I coated the walls with diluted dulux supermatt emulsion (2 coats), which appeared to take fine, and the applied a top coat of a water based emulsion paint within 24hours is has cracked all over again, taking the mist coat along with it. I am now 99% certain that the plaster is fully dried out, so can only assume that there is some sort of chemical reaction occuring between the paint and the plaster. I know that pva was used in the plastering process, is this @pva migration@ as you call it responsible? any nsuggestions would be appreciated.

As an observation, I only ever use the cheapest white matt emulsion I can buy (thinned 25-30%) for priming wash coats, usually whatever is on offer at the sheds which I always leave for 24 hours to dry out thoroughly; the final decorative finish may be a premium brand emulsion but not always, depends what the customer wants. Dulux Supermatt spec. sheet gives a recommendation for use on new plaster even with a residual moisture content but states a maximum thinning of only 20% which personally I think is a little on the low side to ensure good adhesion but I’m not about to argue with ICI who presumably know what they are talking about! How much did you thin it?

I’ve got to say that I’ve never had any problems with "PVA migration"; interesting theory but I’m not sure how it could happen. Can you elaborate in more detail how the render & finish plastering was done; when you say PVA was used in the “plastering process” what exactly do you mean, did your spread use PVA in the plaster mix?

 

[boiler_new]

I actually had to post a reply as i had an extremely annoying problem with pva and the plaster skim coat, basically just had an extension done, we opted for sand and cement and then a skim coat of plaster instead of the hardwall method. When the plasterer came to do the skimming he must have used a lot of pva, and what had happened he plastered on top of wet pva and while working the plaster to get it smooth i am assuming the pva got mixed into the plaster causing nightmares when it came to painting on the fresh plaster, only really had the problem in a few areas, it caused slightly darker patches of plaster and the paint just would not absorb in to the plaster using all the right paints and did the mist coats myself which different levels of water mixed in, but it did require quite a few coats of paint to hide the problem areas and once the final coat of paint went on its not visible anymore but i will not be using blue tack or any tape on that wall because i believe the paint has only formed a layer like what happens when you use vinyl paint instead of matt or supermatt, btw i did use dulux matt paint and then watered down 3 -4 parts paint 2 parts water it worked for me.

Simply if you have this problem of pva migration then you will be able to tell if you have slightly darker patches of plaster on the walls .


never heard of zinsser sealer but if it worked i would have loved to know it a bit earlier

 

[boiler_new]

just a note maybe this problem could have been prevented if the plasterer left the pva too dry out a bit before apply the skimmed coat? not a pro so not entirely sure if its a good idea
but logically the use of pva stops the water from being sucked out from the plaster and allows the plaster to dry uniformly and seals dust if that the whole concept then allowing it to dry completely first seems reasonable?

 

[joe-90]

Your best bet is to use an oil based primer or undercoat. It's much tougher in damp or problem areas.