I herd that prepasted wallpaper should also have paste applied.Is this true?
Also i saw a product by Zinnser called Prepz ,that is wallpaper paste &
sizing all in one.
Has anyone used this & how did it work for you ?

I've done a lot of papering over the years, and generally with pre-
pasted wallpaper. I do the following:

1. Size the wall, especially if it has not been pasted before.

2. Soak the paper in the normal way, as per instructions.

3. Note where the seams are going to go, and brush about a 2" wide
stripe of seam cement at that location.

4. Hang the paper

5. Clean up with a sponge, etc.

This goes a LONG way toward preventing seams from popping over time.