FRESNEL LENS 64" spot Solar concrete crusher Solar can melting
"Fill one bowl with pure Portland Cement halfway and press a second bowl down until the cement squirts out. Let it set for 24 hours. Add water after setting and firm to harden the cement."
Are you saying to fill a bowl with wet Portland Cement & then_ add more water after 24 hours setting? How much water afterwards? Fill the entire bowl with water to "firm the cement?"
Pure portland cement vs adding sand creates a stone like structure vs cement deck. Builders mix because of cost and also decks should have rough surface for wet no slip etc. The lower the sand to cement mix the higher the strength rating. Bowls are small volume so one 80lb bag can make many. Cement is endothermic when hardening. once the_ molded material is firm (cure in the shade higher humidity) about 36hrs. spray with water. After 72 hours fill with water or sink in water.