- Sand fluxes work for wrought iron which has a silica content of its own but sand is not a good flux for steel.
Use borax or a commercial flux for welding modern mild steel.
Also note that beach sand is not "sharp" sand as it has worn round from wave action. Most river sand is sharp.
Silica sand is used as a flux but there are as many types of sands as there are minerals. Many are not good fluxes.
Learning metalworking, metalcraft.
Metal trade education. Hobbysmith.
THE BLACKSMITHS SHOP: Welding. Chapter XXII, ch.22, WELDING, It is often necessay to join together two pieces of iron or the ends of the same piece as in forming a circle., horseshoe, built-up, oxygen, oxide formation, fluxes, reducing fires.