Detaching mud on ceiling, what todo?

Question

I have a ceiling (house from 1956) that was mudded and primed 2 years ago. This was done on top of a new paint job.

The ceiling had originally "popcorn" structure and was mudded flat. However, the mudding job was pretty bad and so I decided to add a layer of topping mud to get it more smooth. On my final lightly sanding phase, I noticed small cracks and stuck a taping knife into it, and found that the initial mud job (or paint?) was not sticking to the old surface. Didn't take me long until I had removed most of the ceiling mud, see picture below. It would come off in large sheets, and was sticking solid only at a few places.

What is the best way forward here?

Tips on what todo with the "islands" that are real hard to scrape off?

I figure

1. I scrape off all that I can scrape off
2. clean the surface (tsp?)
3. prime (not the islands),
4. Re-mud the whole ceiling with heavy all purpose mud?

Or, is there another way? Missing anything?

Regarding primer, can I use Kilz water based or should I use something "better", like a shellac based one, in order to avoid the mud to come off later on, again!

I figure the initial surface was not properly primed (on top of the paint)? Thanks!

Answer 1

I don't think the priming is as much the cause as the surface was not cleaned of dust after the popcorn was removed.

Doing the scraping to remove popcorn texture leaves a great amount of dust on the surface, even if done by wetting and scraping. If the dust is not removed by wiping with a damp sponge or cloth, any paint, primer or drywall compound applied will result in uneven adhesion and a poor look. ( I know. I found out the hard way.)

Unfortunately, in your instance there is no easy fix. You will need to decide if scraping and sanding and recoating is easier or covering with new drywall. (1/4 inch could be done.)

Answer 2

The original mistake was to apply joint compound on top of paint. Paint is designed so that stuff does not stick to it, so that it is easier to clean. This layer of paint needs to be either removed or treated with the appropriate bonding agent.

Regarding the bonding agent, I think that you are confusing paint primer with plastering primer. Paint pŕimer is not made to hold on to joint compound, especially when applying that joint compound to the ceiling. A plastering bonding agent is what you need. Also, note that "drywall primer" is not a primer to mud over. It's a primer to seal the paper in the cardboard, in preparation for painting. Again, what you are looking for is a bonding agent so that joint compound will stick to it.

Once you apply the bonding agent, you can use hot mud to do a first rough layer, then cold mud as a final layer. But in my experience, it's always better to rip the old drywall and install new one. Drywall is super cheap, definitely less than the cost of the mud you will use skimming the area, and definitely less than the cost of your labor. Some will suggest that you install new drywall on top of the old one. It's not my way of doing things, but it is an option too.