Hole at the end of a 6011 weld

Hi folks,

I did a fair bit of welding with 6011 electrodes (4 mm diameter) when build ing my new workbench. I noticed that it's hard to avoid a small, irregular hole remaining in the weld pool at the end of the weld (after solidificatio n). I've noticed this in the past, but it's especially pronounced with the larger electrodes. The steel is between 6 mm and 12 mm thick and I prepared the edges by grinding to give good penetration. Here's a picture of the ho les:

I've tried filling the weld pool for a few seconds before finishing the wel d, but it doesn't avoid the hole. Any ideas how to resolve this? It's not a big issue, but I'd like to correct it on future projects.

Best wishes,

Chris