The basement walls of my recently-built cabin were constructed of cinder blocks which were then painted by the builder. The mortar joints were not done neatly, and the wall is quite rough and uneven. I want to smooth it out with cement or joint compound/mud or something to make a smooth wall. However I am worried about adhesion to the paint. What's the best option here, besides placing studs and drywall over it?
Assuming you don't want insulation inside (perhaps you'll place that outside and get the benefit of the thermal mass of the concrete inside the insulated envelope, and not lose space?) remove the paint and parge the wall.
Remove the paint can look like a powered wire brush, a pressure washer, chemicals, a time machine to instruct your builder not to paint it, etc.
Parging is troweling mortar or plaster to make a smooth surface.
Alternatively, you could ensure a solid bond and only lose a little space by screwing expanded metal lath to the surface, ignoring the paint, and the expanded metal lath will hold your stucco or plaster without it needing a decent bond to the concrete block behind the expanded metal lath. That would save the time and hassle of paint removal.
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You don't need studs for building structure, so 1-bys would do it. Preferably two layers of 1-bys, horizontal first and then vertical on 18" centers as pseudo studs to affix drywall to; advantage over 2x4's (or 2"2's) is that the two layers gives you spacing to easily route wiring, though you'd need either shallow or surface mounted electrical boxes.
Or glue up sheet insulation and put this drywall-support grid over that. It's an ideal time to add insulation. That gives you the depth for full-size electrical boxes.
Or save some space and change types of hassle by using a combined insulation and studding product. I used InSoFast; there may be competing products. InSoFast goes up with construction adhesive, avoiding the question of anchors into concrete. It has its own wiring channels, so the drywall mounts directly to its face.