When welding downhill slag should not be allowed in the weld pool. why?

In downhill welding, slag can interfere with the formation of a strong, cohesive weld by contaminating the weld pool. If slag is present, it can lead to defects such as inclusions, porosity, and weak spots in the weld. Additionally, the rapid cooling that occurs in downhill welding makes it difficult to properly fuse the metal if slag is trapped, compromising the overall integrity and strength of the weld. Therefore, maintaining a clean weld pool is essential for achieving high-quality welds.