For Private Walls:

Only the friends you invite to your Dump can see the Dump. Dumps by default are private and not displayed anywhere publicly. They are invite-only.

For Public Dumps:

To create a Dump that will be displayed publicly, you must submit your Dumps for approval. Once your Dump is approved, it will be displayed to all friends by default and viewable by all Dumpers to follow.

Learn more about Public Dumps here