Paint bubbling in bathroom

[Dbas]

Hi all,

 

We got our bathroom redone a couple of months ago, and the walls were replastered and repainted. Just recently, bubbles have started appearing just on one section of the walls. They only appear after showers, and when the bathroom has cooled down the bubbles disappear.

 

Our contractor is insisting that he's never seen this problem before, and that he had paid for quality bathroom paint for the painter.

 

Can anyone advise what could have caused it? Wrong paint / primer / waiting times not sufficient?

 

I attach a photo below, I hope it's clear enough.

 

Many thanks in advance.

Edited July 4, 2017 by Dbas

[Nickfromwales]

Looks like trapped moisture in the wall or unsuitable paint. Do you know if the plaster was allowed to fully dry prior to painting, and what paint was used? 

[Dbas]

Hi @Nickfromwales, thanks for the reply.

The plaster was given the full weekend to dry (Sat and Sun). I don't know what paint was used, but thinking back, I wonder if the plasterer didn't plaster over that section of the wall because that one happened to already have paint on it. So then when the painter came, he just painted over that old paint plus the other newly plastered walls. There is a slight different in colour between that section and the rest, so either that was the case, or a different paint was used.

 

Do newly plastered walls and old painted walls require different primers?

[Jeremy Harris]

My experience was that a newly plastered wall takes a week or two to dry out.  The surface may have been dry after a weekend, but the chances are that there was still moisture deeper in the plaster, and when covered with a moisture impermeable bathroom paint, that's come up to the surface and caused the bubbles.

 

You can get away with painting over new'ish plaster with something like ordinary emulsion, that will let any trapped moisture come out, but probably not with a water resistant bathroom paint that forms a waterproof skin on the surface.

[Barney12]

Those 'micro blisters' are almost certainly a reaction to the surface underneath. Its a common paint problem.

They become more evident in damp/moist conditions simply because the emulsion absorbs some moisture and expands. 

Without knowing what was on the wall before its hard to comment further but it's could be something as simple as a build up of soap scum which is common in bathrooms. Were the walls scrubbed with sugar soap before painting over the previously painted area? 

 

As as for the solution. There is unfortunately only one:

 

Key it back and add a primer sealer. I would recommend Zinser Bullseye http://www.zinsseruk.com/product/bulls-eye-1-2-3/

Then paint it again.

 

Any shortcut from the above will end in tears. 

 

Edit: Sorry I should have said at the beginning that the above is written on the assumption your builder had painted onto an existing surface. 

 

 

[RichS]

As JSH says, "the full weekend" is nowhere near long enough to let the plaster dry properly.

 

[Dbas]

Thanks all for your replies. The painter that did our walls just gotten back to me -- he said it was probably the new paint reacting with the old paint on that particular part of the wall. It looks like we might have to pay extra to get this sorted. The walls were not scrubbed with soap, nor was the shower room used for at least a week before painter came previously, so trapped moisture shouldn't be an issue. Our contractor claims he has never encountered this problem before.

 

Can I check -- was he supposed to have sanded down the old paint prior to painting as a preventive measure against blistering? Or do anything else to the part that was painted previously? 

Any advice gratefully received, thanks in advance.

[Nickfromwales]

At the absolute bare minimum it should have been sugar soaped and scrubbed clean, then rinsed with clean water. 

If it was a silk or eggshell then it should have been prepped accordingly eg scratched and or sealed prior to new paint going on. 

I'd offer to pay for the paint if they remove the u/s coat and reapply it properly for free, that way it's only time and not money for them. It really should be totally free but all depends how good the relationship is.  

[Dbas]

Ah right. I didn't know they were supposed to soap and scrub the old painted part clean first. This definitely didn't happen because they applied primer straightaway on their first visit. 

 

To remedy bubbles appearing after showers, 

2 hours ago, Nickfromwales said:

they remove the u/s coat and reapply it properly for free,

 is the "u/s coat" you mention this current layer of paint? As in they'd have to scrap this layer (and the bottom old layer?) off? Then scrub it, wait a day to dry, and apply primer. Wait, and then new coat of paint?

 

Painter suggests coming to have a look at the bubbling wall later (which means we turn on the shower to steam up the room for bubbles to appear), he'll take a look, then he'll prime and paint it, all later today. Presumably, with no waiting time in between, this issue won't actually be resolved?

 

Thanks in advance.

[Dbas]

Hi again, would this solution work --  pva coat, replaster and then repaint. Would there be any problems adding more layers on top of this wall that is currently bubbling after showers?

[Nickfromwales]

Sense says to scrape it back and do it once. Only problem is, once you start scraping, re-plastering is your only real option. 

Thistle have a PVA loaded plaster which iirc is only available through the likes of b&q, designed specifically to go over existing painted surfaces. My mate ( plasterer for 30 years ) says it's really good stuff and has used it a few times without issue. It does away with the need for usual 'two coats of plaster over roller applied PVA' so you can put one thinner set on if say skimming to tile trims / other depth sensitive abutting detail like coving. 

[Ferdinand]

 

24 minutes ago, Nickfromwales said:

Sense says to scrape it back and do it once. Only problem is, once you start scraping, re-plastering is your only real option. 

Thistle have a PVA loaded plaster which iirc is only available through the likes of b&q, designed specifically to go over existing painted surfaces. My mate ( plasterer for 30 years ) says it's really good stuff and has used it a few times without issue. It does away with the need for usual 'two coats of plaster over roller applied PVA' so you can put one thinner set on if say skimming to tile trims / other depth sensitive abutting detail like coving. 

 

Is there any reason you cannot add PVA to normal plaster when mixing?

 

Have sometimes done it with glue with eg cement.

 

F

[Nickfromwales]

It's getting the amount right. It's cheap as chips so not worth experimenting imo. . 

[Temp]

Thanks for the tips as I have a similar issue to sort out.

 

 

[Nickfromwales]

46 minutes ago, Temp said:

Thanks for the tips as I have a similar issue to sort out.

 

 

Link

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[Bsil]

Thanks Nick

Edited July 20, 2017 by Bsil

[Dbas]

Thanks for your thoughts  @Nickfromwales . I asked contractor about sanding beforehand as you suggested, but he said he's never removed paint before. On previous jobs he's used pva and plaster to cover painted walls and so far no issues, as a pva creates a barrier. 

 

With our problematic wall though, and this is in the shower room, will not sanding the wall down cause an issue later?

[Nickfromwales]

This is quite simple. Let him / them sort out the issue the way they see fit . Before any work commences, explain to them that if the issue returns, so will they, at their cost, to repair it again. 

The PVA is used to get adhesion, and not to create a barrier. If the new plaster isn't allowed to completely dry out prior to painting this will go full circle.

Plastering over PVA also requires two coats of skim in the same set ( minimum ) as the PVA tends to cause the first coat to bubble up, and is then nigh on impossible to trowel to any reasonable finish, hence the requirement to go over the top of the first coat with a second 'top' coat as a finisher. 

PVA gets reconstituted with water / moisture so ensure this new plaster has time to fully dry with the room getting as little steam / use as possible during that period. If you have to shower, window open, and then door open straight after to ventilate the room. The fan alone won't be sufficient. It would be a very good idea to hire a dehumidifier, but don't be tempted to use that until the plaster has gone light pink. Some nuggets will say that's dry, but it's not fully dry, as in dry enough to paint with a non-breathable paint. 

Lastly, I'd look long and hard at the paint you choose to apply. Go for a top quality paint which is vapour permeable if possible. I for one, would never use a silk paint in a bathroom, but that's your choice, and would instead use a scrubbable matt paint like the Dulux Diamond range. That again is dependant on what is over the other walls already and how far your going to go with this. . 

Tell them the buck stops with them, and the problem won't go away, and you will pursue them if it's not resolved in the next visit.