diff --git a/README.md b/README.md
index 461c10c8..cba647e5 100644
--- a/README.md
+++ b/README.md
@@ -192,6 +192,11 @@ Conform to the following conventions:
     If they both use set -e and cp -n then the conflict will be caught and cause
     the build to fail.
 
+* If your element mounts anything into the image build tree ($TMP\_BUILD\_DIR)
+  then it will be automatically unmounted when the build tree is unmounted -
+  and not remounted into the filesystem image - if the mount point is needed
+  again, your element will need to remount it at that point.
+
 Make as many of the following subdirectories as you need, depending on what
 part of the process you need to customise:
 
diff --git a/elements/base/finalise.d/02-remove-ccache b/elements/base/finalise.d/02-remove-ccache
new file mode 100755
index 00000000..b550f726
--- /dev/null
+++ b/elements/base/finalise.d/02-remove-ccache
@@ -0,0 +1,4 @@
+#!/bin/bash
+set -e
+
+rmdir /tmp/ccache || true
diff --git a/lib/img-functions b/lib/img-functions
index 40844d64..845e3261 100644
--- a/lib/img-functions
+++ b/lib/img-functions
@@ -16,16 +16,14 @@
 function unmount_image () {
     # unmount from the chroot
     # Don't use TMP_MOUNT_PATH here, it might not have been set.
-    sudo umount -f $TMP_BUILD_DIR/mnt/sys || true
-    sudo umount -f $TMP_BUILD_DIR/mnt/proc || true
-    sudo umount -f $TMP_BUILD_DIR/mnt/dev || true
-    sudo umount -f $TMP_BUILD_DIR/mnt/tmp/in_target.d || true
-    sudo umount -f $TMP_BUILD_DIR/mnt/tmp/ccache || true
+    local MOUNTS
+    MOUNTS=$(grep < /proc/mounts " $TMP_BUILD_DIR/mnt" | awk '{ print $2 }' | sort -r)
+    for M in $MOUNTS; do
+        sudo umount -f $M || true
+    done
     # give it a second (ok really 5) to umount XXX - why? should instead track
     # the mount data / lsof etc.
     sleep 5
-    # oh ya don't want to forget to unmount the image
-    sudo umount -f $TMP_BUILD_DIR/mnt || true
     # having disk corruption issues; one possibility is qemu-nbd not flushing
     # dirty pages on disconnect?
     sync
@@ -84,8 +82,6 @@ function run_d_in_target () {
       check_break after-$1 run_in_target bash
       sudo umount -f $TMP_MOUNT_PATH/tmp/in_target.d
       sudo rmdir $TMP_MOUNT_PATH/tmp/in_target.d
-      sudo umount -f $TMP_MOUNT_PATH/tmp/ccache || true
-      sudo rmdir $TMP_MOUNT_PATH/tmp/ccache
     fi
 }