Chris Bacon wrote:

Rob Morley wrote:

Primer doesn't give much build, it's the undercoat that you sand for a
smooth finish.


You shouldn't "sand" primer at all.

Depends what primer and what you are doing.
Alot of promers raise the wood grain, and need sanding and a second
coat - especially cellulose.

When painting car bodies and fibreglass we uwse many primer coats to
cover up scratches and blemishes, all rubbed down.

I used three coats of acrlyic primer, rubbed down, on the bathroom T &
G. That came up immmaculate after another undercoat rubbed down, and two
top coats, the first one rubbed down.

Of course if you want a crap finish, none of that is necessary.