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helpOld paint bubbling when redecorating (self.DIY)

submitted by jacobo164

I'm about to redecorate a room and painted a section of the wall with sample colours, however came across an issue with the paint bubbling.

Photo of some of the bubbles: https://imgur.com/a/tpHFOvZ

The process I followed was:

  1. Clean wall with sugar soap and rinse with clean water.

  2. Lightly sand and wipe away any dust

  3. Once dried, apply a coat of vinyl Matt white (to help mask the previous pink paint)

While the layer of white was drying, bubbles started appearing on the wall (see photo). Chipping these bubbles would remove multiple layers of the old paint.

Later I washed a different section of the wall and found the bubbles appeared once wet from the sugar soap and rinse.

I've struggled to find information online but from what I understand, this is likely due the previous paint not being applied correctly and a solution would be to remove the old paint back to plaster and move on from there.

Removing the paint will be a huge job and very difficult as the room has a staircase in the corner, meaning part of the wall is 2 stories tall. I'm hoping someone more experienced can offer ideas please.

Thanks

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[–]imoutohere 1 point2 points  (3 children)

What is sugar soap?

[–]TheApocaLuke 0 points1 point  (2 children)

Paint prep soap. Used to come as a powder that looks like sugar.

[–]imoutohere 0 points1 point  (1 child)

Interesting, I would say that you didn’t get the residual soap off the wall and it caused that reaction. Scrape off the bubbles, spot patch. Spot prime and you should be good

[–]jacobo164[S] 1 point2 points  (0 children)

Sugar soap seems to be the UK equivalent of TSP in the USA, however they're formulated slightly differently.

Thanks for the advice, I started scraping off the bubbles to patch (while the wall was slightly wet still from cleaning) and found the top layers of paint came off very easily even where there weren't bubbles. It looks like the best option is to scrape all the paint off back to a layer that is adhered properly.

[–]TheApocaLuke 0 points1 point  (1 child)

If the old paint is still attached firmly you can sometimes just put an undercoat with the sealer/primer you'd use to prep bare plaster. Did you do the test where you score an x and then see if the old paint pulls up with tape?

If you are putting acrylic paint over oil based paint you often need an undercoat anyway.

I've only ever gotten a good result on flaky/cracked/shitty paint by stripping and starting again. Took me two attempts on a big ceiling to learn my lesson.

[–]jacobo164[S] 0 points1 point  (0 children)

Thanks for the suggestion. I just did the X test, the edges of the score came away slightly during scoring which the tape then removed, less than 1mm though.

The adhesion of the old paint seems to be the problem, I washed a new section and attempted to scrape off the bubbles as they appeared... While doing this a whole section of the paint came away, revealing a layer of blue paint. The blue paint seems to have adhered properly so it looks like the best option is to strip the whole wall of the top layers of paint