C4 is not really balanced, it takes forever to craft which is boring, but the real unbalance is that it blows up even reinforced instantly, there is no time or strat to defend from a explosive charge.
I suggest that we remove plastic Explosives, and instead introduce throw-able black powder bombs.
These black powder bombs are thrown at structures and explode on impact, they will deal some AOE damage, but affect the target hit the most.
Using these for siege damage gives the defenders a chance to retaliate, but also makes it so the attackers can have a bit more fun raiding, there are many options when using these powder bombs, you can easily switch targets , you could even make it so the repair function was a hammer swing, so that the more people you have repairing = faster repairs, and the more people throwing black powder bombs = more structure damage, this balances out raids/siege damage based off of numbers, but also means the defenders if outnumbered has a chance to defend via positioning/outgunning/flanking etc.
I for one do not like the idea of begin a chemical engineer/explosives expert and making a timed plastic explosive, I would much rather be able to make many crude black powder bombs and have balanced and more fitting gameplay.