diff --git a/pmb/chroot/init.py b/pmb/chroot/init.py
index 0347f713..245ea576 100644
--- a/pmb/chroot/init.py
+++ b/pmb/chroot/init.py
@@ -8,6 +8,7 @@ import filecmp
 import pmb.chroot
 import pmb.chroot.apk_static
 import pmb.config
+import pmb.config.workdir
 import pmb.helpers.repo
 import pmb.helpers.run
 import pmb.parse.arch
@@ -73,6 +74,8 @@ def init(args, suffix="native"):
     copy_resolv_conf(args, suffix)
     pmb.chroot.apk.update_repository_list(args, suffix)
 
+    pmb.config.workdir.chroot_save_date(args, suffix)
+
     # Install alpine-base
     pmb.helpers.repo.update(args, arch)
     pmb.chroot.apk_static.run(args, ["--no-progress", "--root", chroot,
diff --git a/pmb/chroot/zap.py b/pmb/chroot/zap.py
index 1d873bd9..29951fe8 100644
--- a/pmb/chroot/zap.py
+++ b/pmb/chroot/zap.py
@@ -6,6 +6,7 @@ import math
 import os
 
 import pmb.chroot
+import pmb.config.workdir
 import pmb.helpers.pmaports
 import pmb.helpers.run
 import pmb.parse.apkindex
@@ -72,6 +73,9 @@ def zap(args, confirm=True, dry=False, pkgs_local=False, http=False,
                 if not dry:
                     pmb.helpers.run.root(args, ["rm", "-rf", match])
 
+    # Remove config init dates for deleted chroots
+    pmb.config.workdir.clean(args)
+
     # Chroots were zapped, so no repo lists exist anymore
     args.cache["apk_repository_list_updated"].clear()
 
diff --git a/pmb/config/__init__.py b/pmb/config/__init__.py
index 618d11b8..7a214869 100644
--- a/pmb/config/__init__.py
+++ b/pmb/config/__init__.py
@@ -148,6 +148,10 @@ chroot_device_nodes = [
 # You can force-update them with 'pmbootstrap update'.
 apkindex_retention_time = 4
 
+
+# When chroot is considered outdated (in seconds)
+chroot_outdated = 3600 * 24 * 2
+
 #
 # BUILD
 #
diff --git a/pmb/config/workdir.py b/pmb/config/workdir.py
new file mode 100644
index 00000000..282341c8
--- /dev/null
+++ b/pmb/config/workdir.py
@@ -0,0 +1,87 @@
+# Copyright 2020 Oliver Smith
+# SPDX-License-Identifier: GPL-3.0-or-later
+""" Save, read, verify workdir state related information in $WORK/workdir.cfg,
+    for example the init dates of the chroots. This is not saved in
+    pmbootstrap.cfg, because pmbootstrap.cfg is not tied to a specific work
+    dir. """
+import configparser
+import os
+import time
+
+import pmb.config
+
+
+def chroot_save_date(args, suffix):
+    """ Save the chroot initialization date in $WORK/workdir.cfg. """
+    # Read existing cfg
+    cfg = configparser.ConfigParser()
+    path = args.work + "/workdir.cfg"
+    if os.path.isfile(path):
+        cfg.read(path)
+
+    # Set current date for chroot suffix
+    key = "chroot-init-dates"
+    if key not in cfg:
+        cfg[key] = {}
+    cfg[key][suffix] = str(int(time.time()))
+
+    # Write back
+    with open(path, "w") as handle:
+        cfg.write(handle)
+
+
+def chroots_outdated(args):
+    """ Check if init dates from workdir.cfg indicate that any chroot is
+        outdated.
+        :returns: True if any of the chroots are outdated and should be zapped,
+                  False otherwise """
+    # Skip if workdir.cfg doesn't exist
+    path = args.work + "/workdir.cfg"
+    if not os.path.exists(path):
+        return False
+
+    cfg = configparser.ConfigParser()
+    cfg.read(path)
+    key = "chroot-init-dates"
+    if key not in cfg:
+        return False
+
+    date_outdated = time.time() - pmb.config.chroot_outdated
+    for suffix in cfg[key]:
+        date_init = int(cfg[key][suffix])
+        if date_init <= date_outdated:
+            return True
+    return False
+
+
+def clean(args):
+    """ Remove obsolete data data from workdir.cfg.
+        :returns: None if workdir does not exist,
+                  True if config was rewritten,
+                  False if config did not change """
+    # Skip if workdir.cfg doesn't exist
+    path = args.work + "/workdir.cfg"
+    if not os.path.exists(path):
+        return None
+
+    # Read
+    cfg = configparser.ConfigParser()
+    cfg.read(path)
+
+    # Remove entries for deleted chroots
+    key = "chroot-init-dates"
+    changed = False
+    if key in cfg:
+        for suffix in cfg[key]:
+            path_suffix = args.work + "/chroot_" + suffix
+            if os.path.exists(path_suffix):
+                continue
+            changed = True
+            del cfg[key][suffix]
+
+    # Write back
+    if changed:
+        with open(path, "w") as handle:
+            cfg.write(handle)
+
+    return changed
diff --git a/test/test_config_workdir.py b/test/test_config_workdir.py
new file mode 100644
index 00000000..3543412f
--- /dev/null
+++ b/test/test_config_workdir.py
@@ -0,0 +1,103 @@
+# Copyright 2020 Oliver Smith
+# SPDX-License-Identifier: GPL-3.0-or-later
+""" Test pmb/config/workdir.py """
+import os
+import pytest
+import sys
+import time
+
+import pmb_test  # noqa
+import pmb.config
+import pmb.config.workdir
+
+
+@pytest.fixture
+def args(request):
+    import pmb.parse
+    sys.argv = ["pmbootstrap", "init"]
+    args = pmb.parse.arguments()
+    args.log = args.work + "/log_testsuite.txt"
+    pmb.helpers.logging.init(args)
+    request.addfinalizer(args.logfd.close)
+    return args
+
+
+def test_chroot_save_date(args, tmpdir, monkeypatch):
+    # Override time.time()
+    def fake_time():
+        return 1234567890.1234
+    monkeypatch.setattr(time, "time", fake_time)
+
+    args.work = str(tmpdir)
+    func = pmb.config.workdir.chroot_save_date
+    func(args, "native")
+
+    expected = "[chroot-init-dates]\nnative = 1234567890\n\n"
+    with open(args.work + "/workdir.cfg", "r") as handle:
+        assert handle.read() == expected
+
+    # Write again (different code path)
+    func(args, "buildroot_armhf")
+    expected = ("[chroot-init-dates]\nnative = 1234567890\n"
+                "buildroot_armhf = 1234567890\n\n")
+    with open(args.work + "/workdir.cfg", "r") as handle:
+        assert handle.read() == expected
+
+
+def test_chroots_outdated(args, tmpdir, monkeypatch):
+    args.work = str(tmpdir)
+
+    # Override time.time(): now is "100"
+    def fake_time():
+        return 100.0
+    monkeypatch.setattr(time, "time", fake_time)
+
+    # workdir.cfg does not exist
+    func = pmb.config.workdir.chroots_outdated
+    assert func(args) is False
+
+    # workdir.cfg is empty file
+    with open(args.work + "/workdir.cfg", "w") as handle:
+        handle.write("")
+    assert func(args) is False
+
+    # Write fake workdir.cfg: native was created at "90"
+    with open(args.work + "/workdir.cfg", "w") as handle:
+        handle.write("[chroot-init-dates]\nnative = 90\n\n")
+
+    # Outdated (date_outdated: 90)
+    monkeypatch.setattr(pmb.config, "chroot_outdated", 10)
+    assert func(args) is True
+
+    # Not outdated (date_outdated: 89)
+    monkeypatch.setattr(pmb.config, "chroot_outdated", 11)
+    assert func(args) is False
+
+
+def test_clean(args, tmpdir):
+    args.work = str(tmpdir)
+
+    # 0. workdir.cfg does not exist
+    func = pmb.config.workdir.clean
+    assert func(args) is None
+
+    # Write fake workdir.cfg
+    cfg_fake = "[chroot-init-dates]\nnative = 1337\n\n"
+    with open(args.work + "/workdir.cfg", "w") as handle:
+        handle.write(cfg_fake)
+
+    # 1. chroot_native dir exists
+    os.makedirs(args.work + "/chroot_native")
+    assert func(args) is False
+
+    # workdir.cfg: unchanged
+    with open(args.work + "/workdir.cfg", "r") as handle:
+        assert handle.read() == cfg_fake
+
+    # 2. chroot_native dir does not exist
+    os.rmdir(args.work + "/chroot_native")
+    assert func(args) is True
+
+    # workdir.cfg: "native" entry removed
+    with open(args.work + "/workdir.cfg", "r") as handle:
+        assert handle.read() == "[chroot-init-dates]\n\n"