What did I do wrong?

[Nickae]

Hello

We had an extension, and I painted one of the new rooms with a coat of Dulux Matt emulsion {edit - thinned by 10%}, followed by another normal coat on the upper half of the walls about 4 hours later. My intention was to mask off horizontally and paint the lower half with a couple of coats of a different colour Dulux Matt.

I left the paint to dry for 24 hours, then started applying Frogtape Delicate Surface masking tape, but almost immediately I had to lift a piece to reposition it slightly, and a complete strip of paint came away with it!

Worse, I started the presumably long job of filling in the craters with multiple coats of the original paint, and within 10 minutes the rough edges had started to lift.

So, should I have used a dedicated plaster sealer? Should I have done the mist coat differently? Should I have left the wall to dry for longer before getting masking tape anywhere near it? Something else?

And, any suggestions for how to recover from what is starting to look like a massive disaster?

Thanks

Nick

 

[Nickae]

Well, further to this, I find with a palette knife I am able to cleanly peel of large flakes.
Interestingly, the only exception is the area of original damage (in the middle, in the pic below), that I painted over with a single coat yesterday evening. This is properly stuck to the plaster.
The only difference with this patch is the paint wasn't thinned, and I used a brush, not a roller.

I'm wondering whether I should bite the bullet, scrape the entire room back to plaster and start again. Maybe with a coat of plaster sealer to start this time? Or brush the first coat? Would that make a difference?
Anyone got any ideas?

Ta

Nick

 

[sparkwright]

Can't give you a definitive answer, but you seem short of replies.

MAYBE you didn't thin the first coat enough.

It's always a risk using tape, especially on new surfaces.

I think a layer of fine surface filler or similar would have been more preferable than trying to fill with layers of paint.

All bare plaster areas of repair should by rights be spot primed with thinned emulsion IMO.

Scraping it all off could a major task, there's bound to be sections that won't come off easily (unless you think otherwise).

It's possible painting over the existing paint could loosen it all off.

 

[JohnD]

On the paint you peel off, is there dust stuck to the back?

When you mist-coated, did the thinned paint soak into the surface and disappear?

Has anyone put glue on the wall?

 

[Mottie]

On bare plaster I always use a really weak (50/50 ish) emulsion/water mix to seal the wall.

 

[sparkwright]

For the inexperienced, I think painting bare plaster is quite a risky business actually, when you consider what can happen.

I believe you can get 'mist coat' already made up, which could be reassuring to the user - anyone know if this is good enough to use?

 

[HERTS P&D]

I always use a 50/50 on new plaster and never had a problem.

Andy

 

[Nickae]

Many thanks for the useful info and suggestions.

I had thinned the first coat of paint by 10% because that was the instruction on the paint tin. However, it certainly didn't soak into the surface and disappear - is that what is supposed to happen with a mist coat? If so, then I guess the 50/50 mix would have been a better bet.

Whilst waiting to hear back, I went in with the palette knife and scraped off any loose material in the 'critical' area where the colour change is going to be. As stated though, it was only certain areas where the paint was falling off, so I stopped scraping when I got to sound paint. I then primed the bare plaster with some Mapei sealant that I had to hand, followed by a neat coat of emulsion by brush and a couple with a roller. I had originally used a short pile roller, as the plaster was super smooth, but I wondered whether this had resulted in excessively thin coats, so I switched to a medium pile for the repair job, and this helped blend in the craters too.

As predicted above, these extra coats did cause one more spot to bubble up and start flaking, and again I stripped this off as far as sound paint again. It was like stripping wallpaper - the paint was falling away in flakes the size of my hand. There didn't seem to be any dust on the back, and no-one had glued the wall, by the way. This time, as advised, I used fine surface filler, although the area of bare plaster was too big to fill completely (best part of a sq metre), so I just used the filler to feather the edges. The areas I repainted after sealing the plaster seem fine, so I'll do the same with this area tomorrow, followed by a couple of coats of the emulsion.
Then I'll wait a good few days, and try again with the masking tape.

I think for the remaining rooms, I'll use Dulux plaster sealer first!

Thanks again for your help

Nick