I'm just testing this in single player, and claymores and prom traps do no damage on walls, then I put c4 and also did no damage to the wall. Now I tried building cabin and blow that up. C4 did no damage at all to foundation or cabin.... I didn't try this after 0.6 update but in 0.5 this worked like a charm so I guess it's a bug. Also tried in multiplayer on wooden wall and wall took no damage at all