These 20 cm long concrete samples are cored from a cracked concrete wall. A coat of Penetron was brushed onto the top end of one of the cores and afterwards, both cores were put in water with the top ends remaining above water. After 28 days, the cores were taken out of the water and allowed to dry. It then became visible that the crack in the Penetron-treated sample was completely filled with white crystals, demonstrating the ability of Penetron crystals to seal cracks deep into the concrete, as long as water is present. There was no change to the crack in the untreated sample.