diff --git a/Manuals/FDS_User_Guide/FDS_User_Guide.tex b/Manuals/FDS_User_Guide/FDS_User_Guide.tex
index d4b47b80cde..ebda58bdf62 100644
--- a/Manuals/FDS_User_Guide/FDS_User_Guide.tex
+++ b/Manuals/FDS_User_Guide/FDS_User_Guide.tex
@@ -13812,6 +13812,7 @@ \chapter{Error Codes}
 372  \> {\ct Cannot use FISHPAK\_BC for multiple mesh simulations.                  } \> Section~\ref{sec:periodic}  \\
 373  \> {\ct Cannot have FISHPAK\_BC>0.                                             } \> Section~\ref{sec:periodic}  \\
 374  \> {\ct Numerical Instability - FDS stopped.                                   } \> Section~\ref{info:Errors}  \\
+375  \> {\ct OBST \ldots\ is VARIABLE\_THICKNESS or HT3D and needs a MATL\_ID.      } \> Section~\ref{info:HT3D_Limitations}  \\
      \>                                                                               \>                                     \\
 381  \> {\ct Need more spectral band limits.                                        } \> Section~\ref{info:RADI_Wide_Band}  \\
 382  \> {\ct Spectral band limits should be given in ascending order.               } \> Section~\ref{info:RADI_Wide_Band}  \\
diff --git a/Source/init.f90 b/Source/init.f90
index 3207d069d91..8f19f8d2ec4 100644
--- a/Source/init.f90
+++ b/Source/init.f90
@@ -3848,8 +3848,13 @@ SUBROUTINE FIND_WALL_BACK_INDEX(NM,IW)
 
       IF (OBST_INDEX>0) THEN
          IF (OB%MATL_INDEX(1)<1) THEN
-            OB%MATL_INDEX(1:SF%N_MATL) = SF%MATL_INDEX(1:SF%N_MATL)
-            OB%MATL_MASS_FRACTION(1:SF%N_LAYER_MATL(1)) = SF%MATL_MASS_FRACTION(1,1:SF%N_LAYER_MATL(1))
+            IF (ITER==1.AND.SF%N_MATL>0) THEN
+               OB%MATL_INDEX(1:SF%N_MATL) = SF%MATL_INDEX(1:SF%N_MATL)
+               OB%MATL_MASS_FRACTION(1:SF%N_LAYER_MATL(1)) = SF%MATL_MASS_FRACTION(1,1:SF%N_LAYER_MATL(1))
+            ELSE
+               WRITE(MESSAGE,'(3A)') 'ERROR(375): OBST ',TRIM(OB%ID),' is VARIABLE_THICKNESS or HT3D and needs a MATL_ID.'
+               CALL SHUTDOWN(MESSAGE,PROCESS_0_ONLY=.FALSE.) ; RETURN
+            ENDIF
          ENDIF
          HEAT_SOURCE_OBST(N_LAYERS_OBST) = OB%HEAT_SOURCE
          RAMP_IHS_INDEX_OBST(N_LAYERS_OBST) = OB%RAMP_IHS_INDEX
diff --git a/Verification/Fires/box_burn_away1.fds b/Verification/Fires/box_burn_away1.fds
index bc3e6987961..6f7ed1e6266 100644
--- a/Verification/Fires/box_burn_away1.fds
+++ b/Verification/Fires/box_burn_away1.fds
@@ -23,11 +23,10 @@ computed by the first DEVC.
 
 &SURF ID                   = 'FOAM SLAB'
       COLOR                = 'TOMATO 3'
-      MATL_ID              = 'FOAM'
       VARIABLE_THICKNESS   = T
       BURN_AWAY            = T /
 
-&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20. /
+&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MATL_ID='FOAM' /
 
 &SURF ID='HOT', TMP_FRONT=1100., COLOR='RED' /
 
diff --git a/Verification/Fires/box_burn_away10.fds b/Verification/Fires/box_burn_away10.fds
index ceb71a09026..e3a779cec52 100644
--- a/Verification/Fires/box_burn_away10.fds
+++ b/Verification/Fires/box_burn_away10.fds
@@ -24,12 +24,11 @@ There is an extra flat plate attached to the box adding to the fuel mass.
 
 &SURF ID                   = 'FOAM SLAB'
       COLOR                = 'TOMATO 3'
-      MATL_ID              = 'FOAM'
       VARIABLE_THICKNESS   = T
       BURN_AWAY            = T /
 
-&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20. /
-&OBST XB=0.29,0.30,0.20,0.80,0.20,0.80, SURF_ID='FOAM SLAB', BULK_DENSITY=20. /
+&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MATL_ID='FOAM' /
+&OBST XB=0.29,0.30,0.20,0.80,0.20,0.80, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MATL_ID='FOAM' /
 
 &SURF ID='HOT', TMP_FRONT=1100., COLOR='RED' /
 
diff --git a/Verification/Fires/box_burn_away11.fds b/Verification/Fires/box_burn_away11.fds
index f6bcc854d3a..1f7ac3b7813 100644
--- a/Verification/Fires/box_burn_away11.fds
+++ b/Verification/Fires/box_burn_away11.fds
@@ -19,13 +19,12 @@
 
 &SURF ID                   = 'FOAM SLAB'
       COLOR                = 'TOMATO 3'
-      MATL_ID              = 'FOAM'
       VARIABLE_THICKNESS   = T
       BURN_AWAY            = T /
 
-&OBST XB=0.30,0.31,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MULT_ID='x' /
-&OBST XB=0.30,0.70,0.30,0.31,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MULT_ID='y' /
-&OBST XB=0.30,0.70,0.30,0.70,0.30,0.31, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MULT_ID='z' /
+&OBST XB=0.30,0.31,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MULT_ID='x', MATL_ID='FOAM' /
+&OBST XB=0.30,0.70,0.30,0.31,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MULT_ID='y', MATL_ID='FOAM' /
+&OBST XB=0.30,0.70,0.30,0.70,0.30,0.31, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MULT_ID='z', MATL_ID='FOAM' /
 &MULT ID='x', DX=0.1, I_UPPER=4 /
 &MULT ID='y', DY=0.1, J_UPPER=4 /
 &MULT ID='z', DZ=0.1, K_UPPER=4 /
diff --git a/Verification/Fires/box_burn_away2.fds b/Verification/Fires/box_burn_away2.fds
index 509c10dd295..20c8812a60f 100644
--- a/Verification/Fires/box_burn_away2.fds
+++ b/Verification/Fires/box_burn_away2.fds
@@ -25,7 +25,6 @@ The gas species here is additional SPEC.
 
 &SURF ID                   = 'FOAM SLAB'
       COLOR                = 'TOMATO 3'
-      MATL_ID              = 'FOAM'
       VARIABLE_THICKNESS   = T
       BURN_AWAY            = T /
 
@@ -33,7 +32,7 @@ The gas species here is additional SPEC.
       DT_HRR = 0.01
       DT_DEVC = 0.01 /
 
-&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20. /
+&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MATL_ID='FOAM' /
 
 &SURF ID = 'HOT' TMP_FRONT = 1100. /
 
diff --git a/Verification/Fires/box_burn_away3.fds b/Verification/Fires/box_burn_away3.fds
index c56cecee66c..e63d6b9444b 100644
--- a/Verification/Fires/box_burn_away3.fds
+++ b/Verification/Fires/box_burn_away3.fds
@@ -20,7 +20,6 @@ The gas species here is mixture fraction fuel, burning rate specified.
 
 &SURF ID                   = 'FOAM SLAB'
       COLOR                = 'TOMATO 3'
-      MATL_ID              = 'FOAM'
       VARIABLE_THICKNESS   = T
       BURN_AWAY            = T
       HRRPUA               = 4000. /
@@ -31,7 +30,7 @@ The gas species here is mixture fraction fuel, burning rate specified.
       DT_HRR = 0.01
       DT_DEVC = 0.01 /
 
-&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20. /
+&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MATL_ID='FOAM' /
 
 &SURF ID = 'HOT' TMP_FRONT = 1100. /
 
diff --git a/Verification/Fires/box_burn_away4.fds b/Verification/Fires/box_burn_away4.fds
index 699fc02ba33..29e26cba756 100644
--- a/Verification/Fires/box_burn_away4.fds
+++ b/Verification/Fires/box_burn_away4.fds
@@ -22,7 +22,6 @@ The gas species here is mixture fraction fuel, burning rate specified.
 
 &SURF ID                   = 'FOAM SLAB'
       COLOR                = 'TOMATO 3'
-      MATL_ID              = 'FOAM'
       VARIABLE_THICKNESS   = T
       BURN_AWAY            = T
       HRRPUA               = 2200. /
@@ -37,7 +36,7 @@ The gas species here is mixture fraction fuel, burning rate specified.
       DT_HRR = 0.01
       DT_DEVC = 0.01 /
 
-&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20. /
+&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MATL_ID='FOAM' /
 
 &SURF ID = 'HOT' TMP_FRONT = 1100. /
 
diff --git a/Verification/Fires/box_burn_away5.fds b/Verification/Fires/box_burn_away5.fds
index d3fd402014f..d955b2de65f 100644
--- a/Verification/Fires/box_burn_away5.fds
+++ b/Verification/Fires/box_burn_away5.fds
@@ -26,7 +26,6 @@ The gas species is mixture fraction fuel.
 
 &SURF ID                   = 'FOAM SLAB'
       COLOR                = 'TOMATO 3'
-      MATL_ID              = 'FOAM'
       VARIABLE_THICKNESS   = T
       BURN_AWAY            = T /
 
@@ -34,7 +33,7 @@ The gas species is mixture fraction fuel.
 
 &DUMP SMOKE3D=.FALSE., MASS_FILE=.TRUE. /
 
-&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20. /
+&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MATL_ID='FOAM' /
 
 &SURF ID = 'HOT' TMP_FRONT = 1100. /
 
diff --git a/Verification/Fires/box_burn_away6.fds b/Verification/Fires/box_burn_away6.fds
index 81461682321..b12b739c50a 100644
--- a/Verification/Fires/box_burn_away6.fds
+++ b/Verification/Fires/box_burn_away6.fds
@@ -26,7 +26,6 @@ The gas species is mixture fraction fuel.
 
 &SURF ID                   = 'FOAM SLAB'
       COLOR                = 'TOMATO 3'
-      MATL_ID              = 'FOAM'
       VARIABLE_THICKNESS   = T
       BURN_AWAY            = T /
 
@@ -47,7 +46,7 @@ NU=-1,-5,3,4/
 
 &DUMP SMOKE3D=.FALSE., MASS_FILE=.TRUE. /
 
-&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20. /
+&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MATL_ID='FOAM' /
 
 &SURF ID = 'HOT' TMP_FRONT = 1100. /
 
diff --git a/Verification/Fires/box_burn_away8.fds b/Verification/Fires/box_burn_away8.fds
index 8bc98a4f7c9..7296834a043 100644
--- a/Verification/Fires/box_burn_away8.fds
+++ b/Verification/Fires/box_burn_away8.fds
@@ -22,7 +22,6 @@ The gas species here is mixture fraction fuel, burning rate specified.
 
 &SURF ID                   = 'FOAM SLAB'
       COLOR                = 'TOMATO 3'
-      MATL_ID              = 'FOAM'
       VARIABLE_THICKNESS   = T
       BURN_AWAY            = T
       MLRPUA               = 0.0733333 /
@@ -37,7 +36,7 @@ The gas species here is mixture fraction fuel, burning rate specified.
       DT_HRR = 0.01
       DT_DEVC = 0.01 /
 
-&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20. /
+&OBST XB=0.30,0.70,0.30,0.70,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MATL_ID='FOAM' /
 
 &SURF ID = 'HOT' TMP_FRONT = 1100. /
 
diff --git a/Verification/Fires/box_burn_away_2D.fds b/Verification/Fires/box_burn_away_2D.fds
index 20e9cf71089..b53b590476d 100644
--- a/Verification/Fires/box_burn_away_2D.fds
+++ b/Verification/Fires/box_burn_away_2D.fds
@@ -27,7 +27,6 @@ The gas species is mixture fraction fuel.
 
 &SURF ID                   = 'FOAM SLAB'
       COLOR                = 'TOMATO 3'
-      MATL_ID              = 'FOAM'
       VARIABLE_THICKNESS   = T
       BURN_AWAY            = T /
 
@@ -35,7 +34,7 @@ The gas species is mixture fraction fuel.
 
 &DUMP SMOKE3D=.FALSE., MASS_FILE=.TRUE. /
 
-&OBST XB=0.30,0.70,0.0,1.0,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20. /
+&OBST XB=0.30,0.70,0.0,1.0,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=20., MATL_ID='FOAM' /
 
 &SURF ID = 'HOT' TMP_FRONT = 1500., DEFAULT = .TRUE./
 
diff --git a/Verification/Fires/box_burn_away_2D_residue.fds b/Verification/Fires/box_burn_away_2D_residue.fds
index 00ab52c870b..6fddb8164b7 100644
--- a/Verification/Fires/box_burn_away_2D_residue.fds
+++ b/Verification/Fires/box_burn_away_2D_residue.fds
@@ -36,7 +36,6 @@ The gas species is mixture fraction fuel.
 
 &SURF ID                   = 'FOAM SLAB'
       COLOR                = 'TOMATO 3'
-      MATL_ID              = 'FOAM'
       VARIABLE_THICKNESS   = T
       STRETCH_FACTOR       = 1.0
       BURN_AWAY            = T /
@@ -45,7 +44,7 @@ The gas species is mixture fraction fuel.
 
 &DUMP SMOKE3D=.FALSE., MASS_FILE=.TRUE. /
 
-&OBST XB=0.30,0.70,0.0,1.0,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=10. /
+&OBST XB=0.30,0.70,0.0,1.0,0.30,0.70, SURF_ID='FOAM SLAB', BULK_DENSITY=10., MATL_ID='FOAM' /
 
 &SURF ID = 'HOT' TMP_FRONT = 1100., DEFAULT = .TRUE./
 
diff --git a/Verification/Heat_Transfer/ht3d_demo.fds b/Verification/Heat_Transfer/ht3d_demo.fds
index b8ff6923335..88bdae29c7a 100644
--- a/Verification/Heat_Transfer/ht3d_demo.fds
+++ b/Verification/Heat_Transfer/ht3d_demo.fds
@@ -12,15 +12,15 @@
 &VENT DB='ZMIN', SURF_ID='OPEN' /
 &VENT DB='ZMAX', SURF_ID='OPEN' /
 
-&OBST XB=-0.20, 0.20,-0.20, 0.20, 0.05, 0.07, SURF_ID='STEEL SLAB' /
-&OBST XB=-0.12,-0.08,-0.12,-0.08,-0.07, 0.17, SURF_ID='STEEL SLAB' /
-&OBST XB=-0.12,-0.08, 0.08, 0.12,-0.07, 0.17, SURF_ID='STEEL SLAB' /
-&OBST XB= 0.08, 0.12, 0.08, 0.12,-0.07, 0.17, SURF_ID='STEEL SLAB' /
-&OBST XB= 0.08, 0.12,-0.12,-0.08,-0.07, 0.17, SURF_ID='STEEL SLAB' /
+&OBST XB=-0.20, 0.20,-0.20, 0.20, 0.05, 0.07, SURF_ID='STEEL SLAB', MATL_ID='STEEL' /
+&OBST XB=-0.12,-0.08,-0.12,-0.08,-0.07, 0.17, SURF_ID='STEEL SLAB', MATL_ID='STEEL' /
+&OBST XB=-0.12,-0.08, 0.08, 0.12,-0.07, 0.17, SURF_ID='STEEL SLAB', MATL_ID='STEEL' /
+&OBST XB= 0.08, 0.12, 0.08, 0.12,-0.07, 0.17, SURF_ID='STEEL SLAB', MATL_ID='STEEL' /
+&OBST XB= 0.08, 0.12,-0.12,-0.08,-0.07, 0.17, SURF_ID='STEEL SLAB', MATL_ID='STEEL' /
 
 &OBST XB= 0.16, 0.18, 0.13, 0.15, 0.08, 0.09, SURF_ID='HOT' /
 
-&SURF ID='STEEL SLAB', MATL_ID='STEEL', HT3D=T, COLOR='BLACK', CELL_SIZE=0.01 /
+&SURF ID='STEEL SLAB', HT3D=T, COLOR='BLACK', CELL_SIZE=0.01 /
 
 &MATL ID='STEEL', DENSITY=7500, SPECIFIC_HEAT=0.5, CONDUCTIVITY=50 /
 
diff --git a/Verification/Heat_Transfer/ht3d_energy_conservation_4.fds b/Verification/Heat_Transfer/ht3d_energy_conservation_4.fds
index 3aaeca61833..7ab1e56cc20 100644
--- a/Verification/Heat_Transfer/ht3d_energy_conservation_4.fds
+++ b/Verification/Heat_Transfer/ht3d_energy_conservation_4.fds
@@ -12,10 +12,10 @@
 &VENT DB='ZMIN', SURF_ID='OPEN' /
 &VENT DB='ZMAX', SURF_ID='OPEN' /
 
-&OBST XB=-0.20, 0.20,-0.20, 0.20,-0.05, 0.05, SURF_ID='SLAB' /
+&OBST XB=-0.20, 0.20,-0.20, 0.20,-0.05, 0.05, SURF_ID='SLAB', MATL_ID='STUFF' /
 &OBST XB=-0.01, 0.01,-0.01, 0.01, 0.06, 0.07, SURF_ID='HOT' /
 
-&SURF ID='SLAB', MATL_ID='STUFF', HT3D=T, COLOR='BLACK' /
+&SURF ID='SLAB', HT3D=T, COLOR='BLACK' /
 
 &MATL ID='STUFF', DENSITY=50, SPECIFIC_HEAT=1.0, CONDUCTIVITY=0.1 /
 
diff --git a/Verification/Heat_Transfer/ht3d_ibeam.fds b/Verification/Heat_Transfer/ht3d_ibeam.fds
index 04f6d87950e..e8341a378ab 100644
--- a/Verification/Heat_Transfer/ht3d_ibeam.fds
+++ b/Verification/Heat_Transfer/ht3d_ibeam.fds
@@ -9,16 +9,13 @@
 
 &RADI RADIATION=F /
 
-&OBST XB=-.2,.2,-.2,.2,.02,.08,   SURF_ID='ADIABATIC STEEL' / bot flange
-&OBST XB=-.2,.2,-.2,.2,.36,.42,   SURF_ID='ADIABATIC STEEL' / top flange
-&OBST XB=-.02,.02,-.2,.2,.08,.36, SURF_ID='ADIABATIC STEEL' / web
-
-&SURF ID='ADIABATIC STEEL', MATL_ID='STEEL', COLOR='GRAY', 
-      HEAT_TRANSFER_COEFFICIENT=0, HT3D=T, CELL_SIZE=0.01 /
-&SURF ID='HOT STEEL',       MATL_ID='STEEL', COLOR='RED',  
-      TMP_FRONT=800, TAU_T=0., HT3D=T, CELL_SIZE=0.01  /
-&SURF ID='HOT STEEL2',      MATL_ID='STEEL', COLOR='GRAY', HEAT_TRANSFER_COEFFICIENT=0, 
-      TMP_BACK=800, HT3D=T, CELL_SIZE=0.01 /
+&OBST XB=-.2,.2,-.2,.2,.02,.08,   SURF_ID='ADIABATIC STEEL', MATL_ID='STEEL' / bot flange
+&OBST XB=-.2,.2,-.2,.2,.36,.42,   SURF_ID='ADIABATIC STEEL', MATL_ID='STEEL' / top flange
+&OBST XB=-.02,.02,-.2,.2,.08,.36, SURF_ID='ADIABATIC STEEL', MATL_ID='STEEL' / web
+
+&SURF ID='ADIABATIC STEEL', COLOR='GRAY', HEAT_TRANSFER_COEFFICIENT=0, HT3D=T, CELL_SIZE=0.01 /
+&SURF ID='HOT STEEL',       COLOR='RED',  TMP_FRONT=800, TAU_T=0., HT3D=T, CELL_SIZE=0.01  /
+&SURF ID='HOT STEEL2',      COLOR='GRAY', HEAT_TRANSFER_COEFFICIENT=0, TMP_BACK=800, HT3D=T, CELL_SIZE=0.01 /
 
 &MATL ID            = 'STEEL'
       SPECIFIC_HEAT = 0.60
diff --git a/Verification/Heat_Transfer/ht3d_mass_conservation.fds b/Verification/Heat_Transfer/ht3d_mass_conservation.fds
index eb3f0776fdf..12e8333d91b 100644
--- a/Verification/Heat_Transfer/ht3d_mass_conservation.fds
+++ b/Verification/Heat_Transfer/ht3d_mass_conservation.fds
@@ -25,12 +25,12 @@
       CONDUCTIVITY       = 5.
       SPECIFIC_HEAT      = 1. /
 
-&SURF ID='CHUNK', COLOR='BROWN', MATL_ID='WOOD', HT3D=T, CELL_SIZE=0.01 /
+&SURF ID='CHUNK', COLOR='BROWN', HT3D=T, CELL_SIZE=0.01 /
 &SURF ID='HOT', TMP_FRONT=1000, COLOR='RED', TAU_T=0, HEAT_TRANSFER_COEFFICIENT=0, DEFAULT=T /
 
-&OBST XB=0.45,0.55,0.45,0.55,0.45,0.55, SURF_ID='CHUNK' /
-&OBST XB=0.35,0.45,0.35,0.65,0.35,0.65, SURF_ID='CHUNK' /
-&OBST XB=0.35,0.65,0.35,0.65,0.64,0.65, SURF_ID='CHUNK' /
+&OBST XB=0.45,0.55,0.45,0.55,0.45,0.55, SURF_ID='CHUNK', MATL_ID='WOOD' /
+&OBST XB=0.35,0.45,0.35,0.65,0.35,0.65, SURF_ID='CHUNK', MATL_ID='WOOD' /
+&OBST XB=0.35,0.65,0.35,0.65,0.64,0.65, SURF_ID='CHUNK', MATL_ID='WOOD' /
 
 &BNDF QUANTITY='WALL TEMPERATURE', CELL_CENTERED=T /
 
diff --git a/Verification/Heat_Transfer/ht3d_mass_conservation_2.fds b/Verification/Heat_Transfer/ht3d_mass_conservation_2.fds
index 0b93d7fc5a1..25065db530d 100644
--- a/Verification/Heat_Transfer/ht3d_mass_conservation_2.fds
+++ b/Verification/Heat_Transfer/ht3d_mass_conservation_2.fds
@@ -23,12 +23,12 @@
       CONDUCTIVITY       = 5.
       SPECIFIC_HEAT      = 1. /
 
-&SURF ID='CHUNK', COLOR='BROWN', MATL_ID(1,1:2)='DRY WOOD','WOOD MOISTURE', MATL_MASS_FRACTION(1,1:2)=0.95,0.05, HT3D=T, CELL_SIZE=0.01 /
+&SURF ID='CHUNK', COLOR='BROWN', HT3D=T, CELL_SIZE=0.01 /
 &SURF ID='HOT', TMP_FRONT=1000, COLOR='RED', TAU_T=0, HEAT_TRANSFER_COEFFICIENT=0, DEFAULT=T /
 
-&OBST XB=0.45,0.55,0.45,0.55,0.45,0.55, SURF_ID='CHUNK' /
-&OBST XB=0.35,0.45,0.35,0.65,0.35,0.65, SURF_ID='CHUNK' /
-&OBST XB=0.35,0.65,0.35,0.65,0.64,0.65, SURF_ID='CHUNK' /
+&OBST XB=0.45,0.55,0.45,0.55,0.45,0.55, SURF_ID='CHUNK', MATL_ID(1:2)='DRY WOOD','WOOD MOISTURE', MATL_MASS_FRACTION(1:2)=0.95,0.05 /
+&OBST XB=0.35,0.45,0.35,0.65,0.35,0.65, SURF_ID='CHUNK', MATL_ID(1:2)='DRY WOOD','WOOD MOISTURE', MATL_MASS_FRACTION(1:2)=0.95,0.05 /
+&OBST XB=0.35,0.65,0.35,0.65,0.64,0.65, SURF_ID='CHUNK', MATL_ID(1:2)='DRY WOOD','WOOD MOISTURE', MATL_MASS_FRACTION(1:2)=0.95,0.05 /
 
 &BNDF QUANTITY='WALL TEMPERATURE', CELL_CENTERED=T /
 
diff --git a/Verification/Heat_Transfer/ht3d_sphere_24.fds b/Verification/Heat_Transfer/ht3d_sphere_24.fds
index 7f70d2bb617..ce2754581e3 100644
--- a/Verification/Heat_Transfer/ht3d_sphere_24.fds
+++ b/Verification/Heat_Transfer/ht3d_sphere_24.fds
@@ -14,7 +14,6 @@
       DENSITY       = 1000 /
 
 &SURF ID='SPHERE'
-      MATL_ID='STUFF'
       HT3D=T
       TMP_FRONT=20.
       TMP_BACK=20.
@@ -22,7 +21,7 @@
 
 &MULT ID='cube array', DX=0.01, DY=0.01, DZ=0.01, I_UPPER=21, J_UPPER=21, K_UPPER=21 /
 
-&OBST XB=-0.110,-0.100,-0.110,-0.100,-0.110,-0.100, MULT_ID='cube array', SHAPE='SPHERE', RADIUS=0.1, SURF_ID='SPHERE', INTERNAL_HEAT_SOURCE=200., CELL_SIZE=0.01 /
+&OBST XB=-0.110,-0.100,-0.110,-0.100,-0.110,-0.100, MULT_ID='cube array', SHAPE='SPHERE', RADIUS=0.1, SURF_ID='SPHERE', INTERNAL_HEAT_SOURCE=200., CELL_SIZE=0.01, MATL_ID='STUFF' /
 
 &VENT MB='XMIN',SURF_ID='OPEN' /
 &VENT MB='XMAX',SURF_ID='OPEN' /
diff --git a/Verification/Heat_Transfer/ht3d_sphere_48.fds b/Verification/Heat_Transfer/ht3d_sphere_48.fds
index f094b041e4e..da68c95cfed 100644
--- a/Verification/Heat_Transfer/ht3d_sphere_48.fds
+++ b/Verification/Heat_Transfer/ht3d_sphere_48.fds
@@ -21,7 +21,6 @@
       DENSITY       = 1000 /
 
 &SURF ID='SPHERE'
-      MATL_ID='STUFF'
       HT3D=T
       TMP_FRONT=20.
       TMP_BACK=20.
@@ -29,7 +28,7 @@
 
 &MULT ID='cube array', DX=0.005, DY=0.005, DZ=0.005, I_UPPER=41, J_UPPER=41, K_UPPER=41 /
 
-&OBST XB=-0.105,-0.100,-0.105,-0.100,-0.105,-0.100, MULT_ID='cube array', SHAPE='SPHERE', RADIUS=0.1, SURF_ID='SPHERE', INTERNAL_HEAT_SOURCE=200., CELL_SIZE=0.005 /
+&OBST XB=-0.105,-0.100,-0.105,-0.100,-0.105,-0.100, MULT_ID='cube array', SHAPE='SPHERE', RADIUS=0.1, SURF_ID='SPHERE', INTERNAL_HEAT_SOURCE=200., CELL_SIZE=0.005, MATL_ID='STUFF' /
 
 &VENT MB='XMIN',SURF_ID='OPEN' /
 &VENT MB='XMAX',SURF_ID='OPEN' /
diff --git a/Verification/Heat_Transfer/ht3d_sphere_96.fds b/Verification/Heat_Transfer/ht3d_sphere_96.fds
index 0117a9cf0ed..5391808c66a 100644
--- a/Verification/Heat_Transfer/ht3d_sphere_96.fds
+++ b/Verification/Heat_Transfer/ht3d_sphere_96.fds
@@ -15,7 +15,6 @@
       DENSITY       = 1000 /
 
 &SURF ID='SPHERE'
-      MATL_ID='STUFF'
       HT3D=T
       TMP_FRONT=20.
       TMP_BACK=20.
@@ -23,7 +22,7 @@
 
 &MULT ID='cube array', DX=0.0025, DY=0.0025, DZ=0.0025, I_UPPER=81, J_UPPER=81, K_UPPER=81 /
 
-&OBST XB=-0.105,-0.1025,-0.105,-0.1025,-0.105,-0.1025, MULT_ID='cube array', SHAPE='SPHERE', RADIUS=0.1, SURF_ID='SPHERE', INTERNAL_HEAT_SOURCE=200., CELL_SIZE=0.0025 /
+&OBST XB=-0.105,-0.1025,-0.105,-0.1025,-0.105,-0.1025, MULT_ID='cube array', SHAPE='SPHERE', RADIUS=0.1, SURF_ID='SPHERE', INTERNAL_HEAT_SOURCE=200., CELL_SIZE=0.0025, MATL_ID='STUFF' /
 
 &VENT MB='XMIN',SURF_ID='OPEN' /
 &VENT MB='XMAX',SURF_ID='OPEN' /