After submerging the sample during the wash test, what action is necessary to ensure proper mixing?

To ensure proper mixing after submerging the sample during the wash test, agitating the sample is essential. Agitation allows for an even distribution of particles and helps to ensure that all aggregates are adequately mixed with the water. This action facilitates the removal of fine particles from the surface of the coarser aggregate and promotes a thorough and uniform wash, which is critical for achieving accurate test results.

Agitation typically involves a systematic disturbance of the sample, which can be achieved through mechanical means or manual stirring. This step is crucial because it ensures that any adhered fines are dislodged and can be adequately separated from the larger aggregate particles, ultimately leading to a more reliable assessment of the aggregate's quality.

The other actions, while they might play a role in different testing scenarios, do not specifically address the requirement for effective mixing after submergence. Soaking alone would not achieve the distribution needed, vibrating might be useful in different contexts but is not the standard for this particular step, and inverting would not provide the necessary agitation to ensure proper mixing.