diff --git a/lib/communicator/Communicator_base.h b/lib/communicator/Communicator_base.h
index 548515cd..a9b99c17 100644
--- a/lib/communicator/Communicator_base.h
+++ b/lib/communicator/Communicator_base.h
@@ -32,117 +32,33 @@ Author: Peter Boyle <paboyle@ph.ed.ac.uk>
 ///////////////////////////////////
 // Processor layout information
 ///////////////////////////////////
-#ifdef GRID_COMMS_MPI
-#include <mpi.h>
-#endif
-#ifdef GRID_COMMS_MPI3
-#include <mpi.h>
-#endif
-#ifdef GRID_COMMS_MPIT
-#include <mpi.h>
-#endif
-#ifdef GRID_COMMS_SHMEM
-#include <mpp/shmem.h>
-#endif
+#include <Grid/communicator/SharedMemory.h>
 
 namespace Grid {
 
-class CartesianCommunicator {
-  public:    
+class CartesianCommunicator : public SharedMemory {
 
+public:    
 
   ////////////////////////////////////////////
-  // Isend/Irecv/Wait, or Sendrecv blocking
+  // Policies
   ////////////////////////////////////////////
   enum CommunicatorPolicy_t { CommunicatorPolicyConcurrent, CommunicatorPolicySequential };
   static CommunicatorPolicy_t CommunicatorPolicy;
   static void SetCommunicatorPolicy(CommunicatorPolicy_t policy ) { CommunicatorPolicy = policy; }
-
-  ///////////////////////////////////////////
-  // Up to 65536 ranks per node adequate for now
-  // 128MB shared memory for comms enought for 48^4 local vol comms
-  // Give external control (command line override?) of this
-  ///////////////////////////////////////////
-  static const int MAXLOG2RANKSPERNODE = 16;            
-  static uint64_t  MAX_MPI_SHM_BYTES;
   static int       nCommThreads;
-  // use explicit huge pages
-  static int       Hugepages;
 
+  ////////////////////////////////////////////
   // Communicator should know nothing of the physics grid, only processor grid.
+  ////////////////////////////////////////////
   int              _Nprocessors;     // How many in all
   std::vector<int> _processors;      // Which dimensions get relayed out over processors lanes.
   int              _processor;       // linear processor rank
   std::vector<int> _processor_coor;  // linear processor coordinate
-  unsigned long _ndimension;
-
-#if defined (GRID_COMMS_MPI) || defined (GRID_COMMS_MPI3) || defined (GRID_COMMS_MPIT)
-  static MPI_Comm communicator_world;
-
-  MPI_Comm              communicator;
-  std::vector<MPI_Comm> communicator_halo;
-
-  typedef MPI_Request CommsRequest_t;
-
-#else 
-  typedef int CommsRequest_t;
-#endif
-
-
-  ////////////////////////////////////////////////////////////////////
-  // Helper functionality for SHM Windows common to all other impls
-  ////////////////////////////////////////////////////////////////////
-  // Longer term; drop this in favour of a master / slave model with 
-  // cartesian communicator on a subset of ranks, slave ranks controlled
-  // by group leader with data xfer via shared memory
-  ////////////////////////////////////////////////////////////////////
-#ifdef GRID_COMMS_MPI3
-
-  static int ShmRank;
-  static int ShmSize;
-  static int GroupRank;
-  static int GroupSize;
-  static int WorldRank;
-  static int WorldSize;
-
-  std::vector<int>  WorldDims;
-  std::vector<int>  GroupDims;
-  std::vector<int>  ShmDims;
-  
-  std::vector<int> GroupCoor;
-  std::vector<int> ShmCoor;
-  std::vector<int> WorldCoor;
-
-  static std::vector<int> GroupRanks; 
-  static std::vector<int> MyGroup;
-  static int ShmSetup;
-  static MPI_Win ShmWindow; 
-  static MPI_Comm ShmComm;
-  
-  std::vector<int>  LexicographicToWorldRank;
-  
-  static std::vector<void *> ShmCommBufs;
-
-#else 
-  static void ShmInitGeneric(void);
-  static commVector<uint8_t> ShmBufStorageVector;
-#endif 
-
-  /////////////////////////////////
-  // Grid information and queries
-  // Implemented in Communicator_base.C
-  /////////////////////////////////
-  static void * ShmCommBuf;
-
-  
-  size_t heap_top;
-  size_t heap_bytes;
-
-  void *ShmBufferSelf(void);
-  void *ShmBuffer(int rank);
-  void *ShmBufferTranslate(int rank,void * local_p);
-  void *ShmBufferMalloc(size_t bytes);
-  void ShmBufferFreeAll(void) ;
+  unsigned long    _ndimension;
+  static Grid_MPI_Comm      communicator_world;
+  Grid_MPI_Comm             communicator;
+  std::vector<Grid_MPI_Comm> communicator_halo;
   
   ////////////////////////////////////////////////
   // Must call in Grid startup
@@ -158,13 +74,13 @@ class CartesianCommunicator {
   virtual ~CartesianCommunicator();
 
  private:
-#if defined (GRID_COMMS_MPI) || defined (GRID_COMMS_MPIT)  || defined (GRID_COMMS_MPI3) 
+
   ////////////////////////////////////////////////
   // Private initialise from an MPI communicator
   // Can use after an MPI_Comm_split, but hidden from user so private
   ////////////////////////////////////////////////
-  void InitFromMPICommunicator(const std::vector<int> &processors, MPI_Comm communicator_base);
-#endif
+  void InitFromMPICommunicator(const std::vector<int> &processors, Grid_MPI_Comm communicator_base);
+
  public:
   
   ////////////////////////////////////////////////////////////////////////////////////////
@@ -181,8 +97,6 @@ class CartesianCommunicator {
   const std::vector<int> & ThisProcessorCoor(void) ;
   const std::vector<int> & ProcessorGrid(void)     ;
   int                      ProcessorCount(void)    ;
-  int                      NodeCount(void)    ;
-  int                      RankCount(void)    ;
 
   ////////////////////////////////////////////////////////////////////////////////
   // very VERY rarely (Log, serial RNG) we need world without a grid