Firstly, go over the area with a sharp taping knife to remove any high spots. By "high" I mean anything obtrusively so or out of the ordinary. Then with a wide taping knife apply at least three thin coats of drywall compound. THATS the hard part! It takes a lot of practice to get a smooth finish. No sanding between coats unless your applications have high spots or ridges. There should be very little sanding required on the last coat

You may actually find it easier and faster to remove the old drywall with the texture and just install new.

You only have to mud seams and joists then, not the entire surface.

A plasterer's trowel will make much faster work of skimming large areas than using drywall knives.

Maker sure you get one with a large enough diameter handle to control the tilt of the trowel.
The one with the tiny (under one inch diameter) handles are too small to be useful.

I agree with take it down or perhaps go over with with some thin new drywall... I went over some old panelling with 1/4 drywall vs trying to tear it out...

As I said before, skim coating is the way to go. If you can not skim coat you will not be able to mud new drywall. If you are not skilled enough to put 3 even coats on, then the only issue will be how much sanding you do. A pro will have virtually no sanding and a diyer will have more sanding. Just more sanding but doable. The taping knife will be much easier to use than a trowel.

If you choose to skim coat. you might want to consider "meshing" the surface with reinforcing mesh similar to the mesh tape used on seams only it comes in 3' width rolls and is a tad more heavy gauged. You can get it self adhering or you can tack it up using spray adhesive. It installs similar to wall papering and you can get it at most masonry suppliers. The mesh will give something for the first coats to grab a hold of as mudding over a painted surface doesn't always give you the best adhesion.

"The taping knife will be much easier to use than a trowel."

A trowel excels at covering large areas quickly and smoothly.

Avoid the trowels with a small diameter handle though.

They are very difficult to rotate to raise the leading edge.

Google skim coating and check out the UTube videos that come up.

I've done both at my house and based on that embedded sand texture you have, I'd have to vote for tearing out the old and putting up new drywall, but it's a close call. I'd worry about the knife skipping around wildly on the "sand grains" but maybe it wouldn't be a big deal. My skim coat worked out well but I put a lot of time into it and I sanded a LOT, something a pro wouldn't have to do as he'd get it smoother with the knives/trowels. I used a 24" wide taping knife and eventually learned to not worry too much about leaving ridges as I could knock then when they dried.

I think we are going to try skim coating and if it doesn't seem like it is going well, we are going to overlay with 1/4 or 3/8" drywall.

We're only dealing with two walls (8 sheets total), so it won't be a big deal if we have to go that route.

Thanks for the advice.

No one has mentioned material, but I think I would use Durabond 90 for the first coat, since it drys so hard and will better fill up the "valleys" between the bumps. I think that will give you a better surface for subsequent coats of mud. Be carefull not to create any high spots with it however, as it cannot really be sanded down like the regular (softer) mud.

I lead toward the trowel, as well, simply because you can get more material on the wall faster with a trowel. If you're more comfortable with a knife, maybe use it for the final coats.

SOS-feeling like this thread might have the answer I need! Skim coating over a really bad knockdown texture. I have done three coats with all purpose lightweight joint compound overall it’s looking pretty good!

Only issue is there are still some high point from the knock down still showing through. I don’t think I can sand them at this stage without destroying all the work I have done. What should I do?

Additionally, on the walls that look ready. I’ve gone over everything with a light and touched up the places I noticed. I’ve run my hand over the wall more times than I can count to make sure it’s smooth. However, I’m really worried that when I paint sections that aren’t level will be very apparent. Does anyone have any other tips to make sure everything is ready to prime and paint? Would priming the walls and then If anything comes through doing another coat be a terrible idea?

It’s been a messy and time consuming process and really can’t wait for it to be over hahah

Thankful for any advice!