You cannot permanently stop an active ceiling water leak from the exterior surface using temporary sealants, tape, or patching compounds. Applying waterproof tape or caulk to the bottom of leaking ceiling drywall is completely ineffective because water pressure from behind will simply bypass the patch or pool dangerously inside the cavity. To stop a ceiling leak, you must locate and repair the root plumbing or roofing source. Verification: Shut off the water supply or fix the roof breach, then cut out the damaged ceiling drywall and replace it.
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