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Discussion Starter · #1 ·
Hi guys, tldr: I've recently painted an interior wall with a history of slight dampness. There is a patch in the corner which blisters and peels off within 1 hour of paint application - what might I do to address this? Can I strip it back, apply a primer like Zinsser clear coat/123, and repaint it to avoid any blistering/peeling? - or will this either not work/result in flashing?

WHAT I DID: I applied EasyFill60 jointing compound to the surface, allowed it to dry (aided by a heat gun), and then sanded (wet-flatten), dusted and cleaned (sugar-soap) the surface. I also scrapped off any loose paint, as part of my prep. I applied first a spot-mist-coat to filled areas, then 2 coats of Johnstone Trade Vinyl Matt Emulsion (thinned 5%), sanding and dusting between coats, and allowing full drying time as recommended by the manufacturer.

THE PROBLEM: Within an hour of applying the paint, it would peel off onto the roller, and eventually blister, getting worse over time. I then tried again a few days later; I scraped off the paint back to the wall substrate, cleaned and dusted it, then filled the space (so as to get a smooth finish), allowed to dry, then repainted (mist coat, then finish coats). Same issue, just over a slightly smaller area.

SOLUTION?: Paint blistering and peeling is normally a sign of moisture transpiration from the substrate, and while the wall was dry to my touch and sight, I figure given its history of damp it probably is a damp issue (although how it peels within the first 1 hour of application confuses me). While it feels like a bad idea to try and seal in moisture, is it worth scrapping, filling and spot-priming the area with something like Zinsser Clear Coat, or a Ronseal Primer, and the painting over that directly? Or should I just call it quits and chalk this one up to dampness?

Any help really appreciated - these forms have been a godsend for me in the past!
 

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Have you tested that area with a moisture meter? Doing so may show that there is more going on there than you suspect.
 
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Discussion Starter · #5 ·
Cut the drywall out and see what's going on in there. Sounds like a leak. Are you a pro..?
Been pro for a couple of years. Would rather not cut out holes in the shop haha, but there is an ongoing damp issue - but as it is very slight in this area I was wondering about a decent primer and repaint 🤔
 

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Discussion Starter · #6 ·
Have you tested that area with a moisture meter? Doing so may show that there is more going on there than you suspect.
I'll pick up a moisture meter and see what it says, thanks for the suggestion :)
 

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Been pro for a couple of years. Would rather not cut out holes in the shop haha, but there is an ongoing damp issue - but as it is very slight in this area I was wondering about a decent primer and repaint 🤔
It doesn't really matter what you prime it with. If it's wet it, will fail. Although yes Gardz would be the best if your gonna go that route.
 

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I don't know the availability of it all in UK, but generally with peeling paint that I'm unsure of the cause/is troublesome, I find solvent based primer works best to seal it in, this would be something like Zinsser Coverstain (available there I think.) then once it's locked in by the Coverstain, a light skim coat and sand with joint compound to feather the peeling paint layers out, then latex primer of some sort, then latex paint. Oil/solvent primer too is less sensitive to moisture and humidity I would say, too.

Also of some note, the UK style plastering while really cool, sometimes troweling stuff down to an absolute mirror or glasslike finish can be bad for paint adhesion, especially without a "strong" primer with a lot of bonding power. I know there's the "mist coat" thing people do there to penetrate those kind of surfaces with normal latex paint thinned down 50/50, but if you're already using setting joint compound (Easyfill 60 seems like a setting joint compound like our Easysand 45) imo you should give it a very light sand with 150/200 grit or so to allow paint to adhere well mechanically. I think in the future for paint work over skimmed plaster like Thistle where you can't sand it, rather than a mist coat over fresh plaster something like Gardz would be way more ideal since it's already very thin and penetrates surfaces well (it's almost identical to stone/grout sealer, actually) but it has strong bonding and sealing properties, whereas thinned down normal latex paint may not have that.
 

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It doesnt matter what you use. you CANT paint over damp surfaces. The cause of the 'dampness' needs to be fixed first...

Also, and Ive just learned this, but 'Sugar Soap' is TSP, which you really shouldnt use inside, unless absolutely necessary, and if so, it needs to be rinsed REALLY good. just DONT do it... I know the UK has Benjamin Moore available now, as I've heard UK painters act like its a miracle paint, which tells me you all use some poor quality materials. Use a quality paint, and you wont need to worry about washing walls, unless there is oil, or nicotine, or some other bad contaminate.

It sounds like youre literally trying to paint a wet surface.... That s NO. period.
 

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Never knew about this product, looks great I think i'll try it. Does it texture-flash as bad as 123 normally does?
What do you mean by 'texture flash?' Ive never had a problem with any kind of flashing with 123. I once had a problem with Gardz flashin on a new home, because I sprayed it and didnt backroll it, but thats certainly wouldnt apply to your situation. I use Gardz or similar anytime I skim coat walls for wallpaper. Look up "problem drywall sealer" and you can find an equivilant product where you're at. If not, 123 is a very good universal primer, just not good at blocking water stains, if thats what you have. you need a solvent primer for that.
 

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Sugar Soaps typically contain sodium salts which are hygroscopic and scavenge humidity & moisture, potentially resulting in osmotic blistering. The residual salts have a tendency to become entrapped beneath and also within the sealer film, and re-wet with subsequent waterborne coatings allowing moisture to permeate the dry film.
 

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It doesnt matter what you use. you CANT paint over damp surfaces. The cause of the 'dampness' needs to be fixed first...

Also, and Ive just learned this, but 'Sugar Soap' is TSP, which you really shouldnt use inside, unless absolutely necessary, and if so, it needs to be rinsed REALLY good. just DONT do it... I know the UK has Benjamin Moore available now, as I've heard UK painters act like its a miracle paint, which tells me you all use some poor quality materials. Use a quality paint, and you wont need to worry about washing walls, unless there is oil, or nicotine, or some other bad contaminate.

It sounds like youre literally trying to paint a wet surface.... That s NO. period.

The UK paint industry is a bit fast and loose with that, with a lot of "damp fix" type products around. Climate-wise and the way things are constructed there it seems like it's a bigger problem than in USA. Also depending on the house/wall a lot of times in UK people have masonry exterior walls, of which if there's no weather barrier between the masonry and the interior wall (ie, bunch of bricks, plaster over the top of them inside) while everything will be structurally sound moisture can creep in as the masonry isn't waterproof, or masonry has plasterboard directly affixed with mortar, and not separate stud walls between like we usually do in USA.

The only solution in that scenario is using one of the clear sealer type products (like Gardz or tile/grout sealer) over your bricks/exterior cement plaster or pebbledash, but even then that's not a sure solution and you need to reapply it relatively often, compared to the US style setup of coating the interior facing of a masonry wall with a liquid waterproofing paint like Drylock or a sheet membrane.
 

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A couple of tid-bits on sugar soap being that many of us North Americans aren’t too familiar with it:

Having worked extensively with caustic soda and sal soda which are the active ingredients in the more traditional sugar soaps, caustic soda aka lye is also a traditional paint and varnish remover.

When washing distemper with sugar soaps containing lye, the lye can saponify the fatty acids in oil bound distempers which are more common in Europe, resulting in blistering when coated over with emulsions. This is also the main reason why sugar soap works great as a grease remover.

Lye in sugar soap is also highly deliquescent. Deliquescency is the ability of a solid to be converted into the liquid phase through atmospheric moisture absorption such as vapor transmission through exterior walls. The presence of residual lye can increase the substrate’s moisture content due to lye being a moisture scavenger, also increasing the likelihood of blistering on surfaces with pre-existing dampness issues.

A couple of years ago I was working with mild caustic soda in a humid interior environment. After washing everything down and wiping it dry, yet not rinsing and/or neutralizing, a couple of days later, all the surfaces treated with it were sopping wet to the point where moisture was literally running down vertical surfaces and puddling where meeting floors, yet non-treated surfaces remained bone dry. That scenario provides a pretty good illustration of how sugar soap residue behaves as a moisture scavenger and can result in blistering.
 
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