Here's how you can block Facebook friends from seeing your past posts, as well as future posts.
1. Go to your friend's timeline on Facebook.
2. Put your cursor over the Friends button.
3. Select the Restricted list.
4. Now go to Privacy Settings.
5. Scroll down to Limit the Audience for Past Posts.
6. Click on Manage Past Post Visibility.
7. Click the Limit Old Posts button.
8. Click the Confirm button.
Now your friend will not be able to see your past posts, or your future posts (as long as you keep him on the Restricted filter). When your friend goes to your timeline, they will not see the posts there.