I've searched for a similar problem but can't seem to find anything. Maybe I'm using the wrong term?

While cleaning/prepping my slab there is spot that has obviously been patched.
There's about a 2' x 3' area with a completely different texture. I noticed that the surrounding areas sounded "hollow". While I was using a Diamabrush wheel on a floor polisher it started flaking off all over the place. Now I can lift pieces of the concrete off with my finger. Guessing it's a bad patch. My question is, how to deal with this? Do I need to identify all of these "flaky" areas and chip it all away? Don't want to go to all the trouble of applying a leveling compound if it's just going to flake with the rest of the slab. FYI: I tapped on the "hollow" areas with my prybar and hammer and it didn't crack or come up.

Hope I explained that clearly. Could load some pics later, if that would help.

Thanks,

Matt

Are you scouring the slab in preparation for glue-down? If the patch is secure when tapping on it, you would only need to patch where it is low, again. I presume you got all the spalling concrete removed.
This is a judgement call, but a latex underlayment mix may be all it needs.

Yes, prepping for glue down. Forgot to mention that.

No, I haven't removed all of the spalling but I think your question tells me what I need to do.
I will break up and remove any spalling (identified by "hollow" sound when tapping on surface. Clean rest of slab as normal. Pour leveling compound. Sound right?

One last question: Does leveling compound need any further prep? Other than a proper cure, of course.

I always check with a straight-edge and use an edger with 16 grit paper to fine tune where it is needed.