The Temple Institute: In-Depth Temple Study: The Mizbeach
 
The Mizbeach (continued)

The mizbeach must stand upon earth, and is referred to as the "earthen Mizbeach." This altar may not stand over tunnels or elevated arches as do the other floors of the Temple Mount and the Mikdash. The mizbeach was whitewashed twice a year, on Passover Eve and on Sukkot eve. It was cleaned every Shabbat eve. 
Contents:   Part I,    Part II,    Part III