Jan 01, 2013 · 4´ deep koi pond with 4˝ bottom drain, 2˝ fiber reinforced ncrete sprayed over 45mil EPDM liner. ncrete and mortar have been favored by pond nstruction and fountain builders since the Roman Empire, and the formula has changed little in the past 2000 years. Limestone and clay are mixed, heated and ground to the silky powder we call cement.