Translations:Adventist Youth Honors Answer Book/Household Arts/Cultural Food Preparation/11/en
From Pathfinder Wiki
3. Stones
Stones should be smooth river stones, though bricks can do the job as well. They should be 10 cm to 15 cm across, and the more uniform they are in size, the better. You will need enough to line the bottom of the lovo. Be sure to select stones that will not explode when heated (gravel will explode, as will concrete and cement).