how soon can painted walls be sanded down?

londonTiger

My brother painted my wall, I didn't like a lump on the wall, so I attacked it with a sander just 24 hours after it was applied. The paint just came off right down to the plaster wall. there;'s about 4 layers of paint on the rest of the wall and now there's plaster wall visible.

The newly applied paint soaked into the other paint layers and weakened it, so I started scraping and ended up delayer all the paint. Now I have to smooth it out.

I am going to leave it for as long as possible for the paint to dry and set completely so now it gets sanded off rather than peel off. How long should I wait?

Mojisola

It's possible that the first coat of paint on the plaster was put on at full strength. The first couple of coats need to be watered down so that the paint is drawn into the plaster. If this doesn't happen, the paint doesn't stick properly to the plaster and can lift away like a sheet of paper if disturbed.

keystone

First its almost certain that Mojisola is correct that a mist coat was no properly applied so that paint has not adhered to the plaster.

Second Emulsion paint takes a full 30 days to fully cure.

Thirdly you were barmy to attack it with a power sander in any event and what you've done is make things worse. Anything but a light abrasion by hand with a fine grade abrasive will take off far more than you expect.

So you have two choices - fix the current problem or start again. For the first feather the edges of the existing paint, fill it back flush with a fine surface filler. Whack a coat of spirit based undercoat over the filled area. Lightly abrade the whole of the wall by hand using a 200 or 300 grade abrasive and repaint the whole wall.

For the second scrape all the unadhered paint off the whole wall with a sharp scraper. Its sounds as though it will just peel off in sheets. Then repaint properly this time. Mistcoat first, second coat using your finish thinned by about 10% then top coat neat.

Cheers

cyclonebri1

As above with variation.

I assume only a small area of wall is down to the plaster?

The 1st thing is that seeing as you have caused so much pain trying to remove the "bump", to ensure you have actually removed it all.
No point refinishing to find that you can still see it.
And conversely ensure you have now not created a hollow in place of the bump. Straight edge across the affected area is in order.

Fill or sand further as required, then leave for at least 2 weeks, 4 if you have the patience, then restart the painting process ensuring that the bare plaster or filler is totally obliterated by the recoats, before repainting the whole wall.

I have found that you can get away with a carbide grit sanding plate on a 3rd sheet sander as it doesn't clog as readily, but seeing as the paint will not have fully cured in a few weeks it may still "ball" up.

And no, I didn't mean balls up, although that would be the eventual outcome,:D:D