Stain Blocking Primers.  Stain blockers lock in stains and prevent them from migrating into the finish paint.   The stain blocking capabilities of each of the universal primer types is different depending on the type of stain.  Water based stain blockers for example, do not work well withwater soluble stains, whereas shellac or oil stain blockers will seal water soluble stains effectively. It is important to use the right primer for the right stain blocking task.  For more tips, visit us on YouTube “idahopainters” or see us on the web.