Can I apply drywall mud directly to a concrete block wall?

I am prepping a wall in my school's library for a mural. It is an interior wall with high gloss paint.
I have sanded the wall and cleaned it with soap and water. I used 60 grit sand paper.

Can I apply drywall mud directly to the wall to smooth it out for painting.
I am planning on applying an acrylic filler primer before painting.
Any help will be appreciated.

 

Welcome to the forums! I doubt the results with drywall compound will be good or permanent as you would think. I would hate to advise you it would work, and after the beauty is up, it begins to crack and fall off the wall.
Others will chime in with better advice, I am sure, but I believe a concrete product to skim coat the block would work much better than mud. How big will the mural be?

 

Sheetrock mud is not the type of compound used on plaster walls. Real plaster or stucco might work. Have you considered doing a fresco. Fresco - Wikipedia, the free encyclopedia

 

The mural is approximately 8' tall by 24' long. Any suggestions as to what type of concrete product I should use?

 

The suggestions for the type of coating will come. But as long as you're researching, find out what will give you he texture you'll need and if you'll need to seal the coating so that it will take whatever type of paint you'll use in a somewhat predicatable way. Think of what you're used to painting on in other words.
I'm liking the real plaster idea.
But perhaps you can do a moisture test on an area as step one.

 

Well,

Too bad it's painted. It would be easy to plaster with gypsum plaster which would give you a nice smooth, straight finish. If this is an interior wall I think bonding agent like Plaster-Weld by Larsen's or Larson's Products would be great to plaster over. Plastering this is not something you want to try yourself.

I suspect you are wanting something you can do yourself. Will the mural be out of the reach of the traffic? Will it get banged up by people and sporting equipment? If not then I think drywall mud should work. Start with a setting type like EasySand and spread it as tightly as you can. Just fill the joints and pores. Lay it on as thinly and as smooth as possible. As soon as it sets cut off the ridges and beads and give it another tight coat. After that has set and dried give it a sanding to get rid of the ridges and beads. Maybe you will think this is good enough. If so then prime it appropriately and paint. If it isn't good enough then use regular joint compound and give it another tight coat and then when it is dry sand, touch up any flaws and prime and paint.

Whatever you do, don't try to use cement plaster or gypsum plaster without a bonding agent, unless you lath it first.