Termites will put a lot of effort into breaking through something that stands between them and the food or water they desire. Just so long as the prize justifies the effort required, they will appear as if to move mountains. Plaster (drywall etc.) is no barrier to termites. Most mortars slow them down, but lime mortars are readily penetrable. Termites will not usually do any damage to quality mortars with a high cement content, but beware of gaps and shrinkage cracks. Good quality concrete cannot be excavated by termites BUT cracks in poor concrete may be opened with ease. Autoclaved aerated concrete (those lightweight bubbly blocks) were readily penetrated in my field tests. Concrete (cinder) blocks sometimes have gaps in them big enough to interest termites (also observed in my field trials). Masonry is often built with lots of continuous gaps that termites can simply walk through, especially with extruded, hollow-core bricks.
Mud-brick (adobe) can be penetrated but there is most risk between the blocks and at cracks, penetrations and against timber framing.
In general, termites won’t damage concrete if they can’t pull out the sand (and small aggregate) particles. If the cement has been properly proportioned and the mix allowed to cure, then the particles tend to be well bound and termites are adequately deterred.
Termites can walk through cracks in concrete. The cracks need to be uniformly about 10% wider than the termites’ head. Concrete that is properly placed, cured and is reinforced (‘rebar’) generally won’t crack wide enough to be at risk. A properly designed and constructed concrete slab can be a building’s main defence against subterranean termites.
Sometimes concrete has big pockets of air (because it was not properly settled), has wooden levelling pegs left in (termite highways) or has been damaged by expanding bolts or following trades cutting to add services. Easy termite paths are commonly found where floor slabs have cut-outs for baths or showers or where there are pipes or conduits passing through from the ground.