diff --git a/parallel.py b/parallel.py
index 5b565bc..a80ff39 100644
--- a/parallel.py
+++ b/parallel.py
@@ -490,37 +490,57 @@ class PPP:
         self.exchange_ghost_cells(key_out)
         self.impose_boundary_conditions(key_out)
 
-    def init_symmetry(self,key,mirror=(True,True)):
-        '''Sets the symmetries for ghost cells behind the wall'''
-        # Example: wall in y
-        # No-slip boundary (no mirror)  free-slip boundary (mirror)
-        #   u  -> -u                    u  ->  u
-        #   v  -> -v                    v  -> -v
-        #   w  -> -w                    w  ->  w
-        #   p  ->  p                    p  ->  p
+    def init_symmetry(self,key):
+        '''Sets mirror symmetries for ghost cells behind the wall. Use 
+           impose_symmetries_noslip() afterwards to set appropriate
+           no-slip boundary conditions.'''
         import numpy as np
         self.symmetries[key] = np.zeros((3,3,3),dtype='i')
-        if not self.xperiodic:
-            if key=='u':
-                self.symmetries[key][0,1,1] = -1
-                self.symmetries[key][2,1,1] = -1
+        for axis in range(3):
+            self.impose_mirror_symmetry(key,axis,-1)
+            self.impose_mirror_symmetry(key,axis,+1)
+        return
+
+    def impose_mirror_symmetry(self,key,axis,wall):
+        '''Applies symmetry: [u,v,w](x,-y,z) -> [u,-v,w](x,y,z)
+           Proposed by Lozano-Duran JFM 2016 and used for free-slip.'''
+        if self.periodicity[axis]: 
+            return
+        if wall in (-1,'low'): iwall = 0
+        elif wall in (1,'high'): iwall = 2
+        else: raise ValueError('Invalid value for "wall". Valid values are -1 / "low" or 1 / "high".')
+        keyu = ('u','v','w')
+        # Get position in symmetries array to be edited
+        sl = [1,1,1]
+        sl[axis] = iwall
+        sl = tuple(sl)
+        if key==keyu[axis]:
+            self.symmetries[key][sl] = -1
+        else:
+            self.symmetries[key][sl] = 1
+        return
+
+    def set_noslip_bc(self,axis,wall):
+        '''Applies symmetry: [u,v,w](x,-y,z) -> [-u,v,-w](x,y,z)
+           The boundary conditions are only applied to fields which have already been loaded!'''
+        if self.periodicity[axis]:
+            return
+        if wall in (-1,'low'): iwall = 0
+        elif wall in (1,'high'): iwall = 2
+        else: raise ValueError('Invalid value for "wall". Valid values are -1 / "low" or 1 / "high".')
+        keyu = ('u','v','w')
+        for key in keyu:
+            if not key in self.symmetries:
+                continue
+            # Get position in symmetries array to be edited
+            sl = [1,1,1]
+            sl[axis] = iwall
+            sl = tuple(sl)
+            if key==keyu[axis]:
+                self.symmetries[key][sl] = 1
             else:
-                self.symmetries[key][0,1,1] = 1 if mirror[0] else -1
-                self.symmetries[key][2,1,1] = 1 if mirror[1] else -1
-        if not self.yperiodic:
-            if key=='v':
-                self.symmetries[key][1,0,1] = -1
-                self.symmetries[key][1,2,1] = -1
-            else:
-                self.symmetries[key][1,0,1] = 1 if mirror[0] else -1
-                self.symmetries[key][1,2,1] = 1 if mirror[1] else -1
-        if not self.zperiodic:
-            if key=='w':
-                self.symmetries[key][1,1,0] = -1
-                self.symmetries[key][1,1,2] = -1
-            else:
-                self.symmetries[key][1,1,0] = 1 if mirror[0] else -1
-                self.symmetries[key][1,1,2] = 1 if mirror[1] else -1
+                self.symmetries[key][sl] = -1
+        return
 
     def copy(self,key,key_out,skip_data=False,skip_symmetries=False):
         '''Copies a field to a new key.'''