fix

code/game/objects/effects/decals/cleanable/misc.dm

@@ -65,7 +65,11 @@
 	mergeable_decal = TRUE
 	persistent = TRUE
 
-/obj/effect/decal/cleanable/dirt/proc/dirty(strength)
+/obj/effect/decal/cleanable/dirt/Initialize(mapload)
+	. = ..()
+	alpha = CONFIG_GET(number/dirt_alpha_starting)
+
+/obj/effect/decal/cleanable/dirt/proc/dirty(strength = 1)
 	if(alpha < 255)
 		alpha += strength
 		if(alpha > 255)

code/game/turfs/open.dm

@@ -4,8 +4,8 @@
 	var/dirt_buildup_allowed = FALSE
 	/// Dirt level.
 	var/dirtyness = 0
-	/// Dirt level to spawn dirt.
-	var/dirt_spawn_threshold = 100
+	/// Dirt level to spawn dirt. Null to use config.
+	var/dirt_spawn_threshold
 	/// Slowdown applied to mobs on us.
 	var/slowdown = 0 //negative for faster, positive for slower