diff --git a/StandAlone/paths.lua b/StandAlone/paths.lua
index e6fdc039..1a18a7e6 100644
--- a/StandAlone/paths.lua
+++ b/StandAlone/paths.lua
@@ -1,6 +1,7 @@
 -- made by cooldude
 -- idea from Mylon - Dirt Path
 
+local clean_time = 18000 -- time in ticks
 local paths = {
     -- ['tile name'] = {health,convert to}
     -- health is in hundrads of steps
@@ -26,7 +27,6 @@ local paths = {
     ['dirt-3']={10,'dirt-4'},
     ['dirt-4']={5,'dirt-5'},
     ['dirt-5']={5,'dirt-6'},
-    ['dirt-6']={1000,'dirt-6'},
     ['grass-4']={10,'dirt-4'}
 }
 for tile,value in pairs(paths) do
@@ -43,19 +43,33 @@ local function global_key(surface,pos)
     return global.paths[key]
 end
 
+local function remove_key(surface,pos)
+    local key = 'S'..surface.name..'X'..math.floor(pos.x)..'Y'..math.floor(pos.y)
+    if not global.paths then global.paths = {} end
+    global.paths[key] = nil
+end
+
+local function clean_global()
+    if not global.paths then return end
+    for key,tile in pairs(global.paths) do
+        if tile[3] < game.tick-clean_time then global.paths[key] = nil end
+    end
+end
+
 local function down_grade(surface,pos)
     local tile = surface.get_tile(pos).name
     local new_tile = paths[tile][2]
     if new_tile == 'world-gen' then new_tile = global_key(surface,pos)[1] or 'grass-1' end
     surface.set_tiles{{name=new_tile,position=pos}}
     global_key(surface,pos)[2]=paths[new_tile][1]
+    if not paths[new_tile] then remove_key(surface,pos) return end
 end
 
 Event.register(defines.events.on_player_built_tile, function(event)
     local surface = game.surfaces[event.surface_index]
     local old_tiles = event.tiles
     for _,old_tile in pairs(old_tiles) do
-        if not paths[old_tile.old_tile.name] or not paths[surface.get_tile(old_tile.position).name] then return end
+        if not paths[old_tile.old_tile.name] or not paths[surface.get_tile(old_tile.position).name] then remove_key(surface,pos) return end
         if old_tile.old_tile.name ~= 'refined-concrete' and old_tile.old_tile.name ~= 'refined-hazard-concrete-right' 
         and old_tile.old_tile.name ~= 'refined-hazard-concrete-left' and old_tile.old_tile.name ~= 'concrete'
         and old_tile.old_tile.name ~= 'hazard-concrete-right' and old_tile.old_tile.name ~= 'hazard-concrete-left'
@@ -64,24 +78,33 @@ Event.register(defines.events.on_player_built_tile, function(event)
         end
         global_key(surface,old_tile.position)[2]=paths[surface.get_tile(old_tile.position).name][1]
     end
+    global_key(surface,pos)[3] = event.tick
 end)
 
 Event.register(defines.events.on_player_mined_tile, function(event)
     local surface = game.surfaces[event.surface_index]
     local old_tiles = event.tiles
     for _,old_tile in pairs(old_tiles) do
-        if not paths[old_tile.old_tile.name] or not paths[surface.get_tile(old_tile.position).name] then return end
+        if not paths[surface.get_tile(old_tile.position).name] then remove_key(surface,pos) return end
         global_key(surface,old_tile.position)[2]=paths[surface.get_tile(old_tile.position).name][1]
     end
+    global_key(surface,pos)[3] = event.tick
 end)
 
 Event.register(defines.events.on_player_changed_position, function(event)
     local player = Game.get_player(event)
     local surface = player.surface
     local pos = player.position
-    if not paths[surface.get_tile(pos).name] then return end
+    if not paths[surface.get_tile(pos).name] then remove_key(surface,pos) return end
     global_key(surface,pos)[2] = global_key(surface,pos)[2]-1
     if global_key(surface,pos)[2] <= 0 then
         down_grade(surface,pos)
     end
+    global_key(surface,pos)[3] = event.tick
+end)
+
+Event.register(defines.events.on_tick, function(event)
+    if (game.tick%clean_time) == 0 then
+        clean_global()
+    end
 end)
\ No newline at end of file