Is the upgrade info outdated for A13? Right-clicking with the wrench on this wall shows an icon at the bottom-right corner with the missing resource. It's some picture of an upside-down cone with something inside. --22.214.171.124 05:17, 28 February 2016 (UTC)
- You need cement for the next upgrade. The upside-down cone with something inside is a bucket of cement mix. =) If you have 10 of those in your inventory you can upgrade to reinforced concrete.