The safest way to approach questionable concrete is not to cover it over with cbus but to fix the concrete.
Tiling over concrete block wall.
Cinder block wall preparation first the cinder or concrete masonry unit block needs to be prepared correctly.
As for tiling on blockwork it can be done as long as its flat as a pancake every block is perfect then yes spread it on as u would a normal flat wall powdered addy but ive very rarly seen a perfectly flat blockwork wall in fact never.
Cracks and gaps can be filled with portland cement based fillers.
Things you ll need ph neutral cleaner sponge scrub brush 3 4 expanded metal lath 1 1 2 or 2 inch concrete nails hammer tin snips thinset mortar bucket notched trowel ceramic tiles tile spacers plywood board carpenter s level silicone caulking grout grout float lint free cloth.
Id board it mate quicker and you can tile straight away.
The key to a long lasting and attractive tile installation is proper substrate preparation.
Apply commercially made filler that is made specifically for cinder or concrete blocks to create a smooth surface to which the tile can adhere.
Installing tile over concrete walls is possible but presents some unique challenges.
You can get this from construction or hardware stores.
For tiling over tiles in bathroom walls you ll need to set up sheets of waterproof membrane in between the concrete wall and tiles.
Ventilate and dehumidify the area before during and after the installation because basement walls are usually susceptible to moisture.
Any hairline structural cracks sprawling or gaping fissures or chips should be addressed.