Painting old plaster that wasnt primed when it was first painted?

[reb78]

This is a question about old plaster.

I am painting a previously decorated room. In places the emulsion is bubbled and scrapes off to reveal clean plaster. I suspect it was never primed with a mist coat.

What do I do to ensure the new coat of paint doesnt do the same?

 

[Endeleus]

scrape / rub down any loose / bubbling paint, then mist coat as your first coat. If you're really enthusiastic, you could give a quick rub over with a sanding pole (I personally give a very quick once-over with an orbital sander before painting walls where paint is going to the the final finish).

I'm in the midst of painting where there's a mixture of old plaster, new plaster and filler. Usually takes 2 or 3 iterations of rub down, paint, fill, repeat before I'm happy with the end result.

Same approach for me whether its metal, wood or paint.... rub it back until you get to something solid, then use that as the base for repair.

 

[tom2207]

thats a worst case scenario ,,, get the scraper out and peel off anything that will peel , random orbital sand the rest , what ever peels peels ,,, sand off the edges again and repeat ,,, when youve sanded the whole area / room either mist coat it with 50 /50 emulsion , or prime with zinser , or both ,,, then paint again
lining paper is a lot quicker and easier , then zinser and paint it instead ,,,, all in all its a grim job.

 

[Nomad]

Pull / scrape off any loose, sand the edges smooth, mist coat 50/50 water & *matt* emulsion.
When it's all dry I use superfine filler to blend the edges, sand the filler when it's had a day to dry.

Don't try to use Silk for a mist coast - it needs to breath or you get more blistering. Ask me how I know.

 

[dan.taylor.1]

This happened in our bathroom even though we did mist it. Used some special primer on the wall with the issue and painted bathroom paint over that.