The purple bleed-through on the ceiling after using Kilz-2 is likely caused by the water based primer reactivating a sub-surface stain. When dealing with stains such as purple bleed-through, it is essential to properly clean and prime the surface to prevent them from seeping through the new paint or primer.

In this case, the purple bleed-through is most likely due to water stains or other contaminants present on the ceiling that were not adequately sealed before applying the Kilz-2. To address this issue, it is recommended to thoroughly clean the ceiling to remove any existing stains or dirt. After cleaning, apply a stain-blocking primer specifically designed to seal water stains and other stubborn contaminants, a shellac or oil based primer would be a good choice. Kilz also offers specialty primers for such purposes.

Another factor to consider is the application of multiple coats of primer and paint. If the first coat of Kilz-2 did not fully cover the purple bleed-through, applying an additional coat may be necessary to ensure complete coverage and block the stains effectively.